Re: Libpq support to connect to standby server as priority

From 0ac2c799bd6bc75ba039520dcf8474be52688e7b Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 7 Jun 2018 18:11:51 +1000
Subject: [PATCH] Allow target-session-attrs to accept prefer-read option

With this new prefer-read option, the connection is preferred
to connect to a read-only server if available in the connection
string, otherwise connect to a read-write server.
---
 doc/src/sgml/libpq.sgml               |  13 ++-
 src/interfaces/libpq/fe-connect.c     | 208 ++++++++++++++++++++++++++--------
 src/interfaces/libpq/libpq-int.h      |   3 +-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 4 files changed, 189 insertions(+), 49 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 498b8df988..05562e1ec0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1592,8 +1592,17 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         successful connection; if it returns <literal>on</literal>, the connection
         will be closed.  If multiple hosts were specified in the connection
         string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
+        attempt had failed.
+      </para>
+      <para>
+        If this parameter is set to <literal>prefer-read</literal>, a connection
+        in which read-only transactions are supported server is preferred. If
+        failed to connect to a read-only transactions supported server, then
+        a connection to the read-write transactions supported server is accepted.
+      </para>
+      <para>
+        The default value of this parameter,<literal>any</literal>, regards all
+        connections as acceptable.
       </para>
       </listitem>
     </varlistentry>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index a7e969d7c1..9b16d57e0d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -327,7 +327,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1184,7 +1184,8 @@ connectOptions2(PGconn *conn)
 	if (conn->target_session_attrs)
 	{
 		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+			&& strcmp(conn->target_session_attrs, "read-write") != 0
+			&& strcmp(conn->target_session_attrs, "prefer-read") != 0)
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -2086,8 +2087,23 @@ keep_going:						/* We will come back to here until there is
 					{
 						if (++conn->whichhost >= conn->nconnhost)
 						{
-							conn->whichhost = 0;
-							break;
+							if (conn->read_write_host_index >= 0)
+							{
+								/*
+								 * Go to here means failed to connect to
+								 * read-only servers and now try connect to
+								 * read-write server again. Only under the
+								 * 'prefer-read' scenario will go to here.
+								 */
+								conn->addr_cur = conn->connhost[conn->read_write_host_index].addrlist;
+								conn->whichhost = conn->read_write_host_index;
+								conn->read_write_host_index = -1;
+							}
+							else
+							{
+								conn->whichhost = 0;
+								break;
+							}
 						}
 						conn->addr_cur =
 							conn->connhost[conn->whichhost].addrlist;
@@ -2112,6 +2128,14 @@ keep_going:						/* We will come back to here until there is
 							conn->addr_cur = addr_cur->ai_next;
 							continue;
 						}
+						else if (conn->read_write_host_index >= 0)
+						{
+							conn->addr_cur = conn->connhost[conn->read_write_host_index].addrlist;
+							conn->whichhost = conn->read_write_host_index;
+							conn->read_write_host_index = -1;
+							continue;
+						}
+
 						appendPQExpBuffer(&conn->errorMessage,
 										  libpq_gettext("could not create socket: %s\n"),
 										  SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
@@ -2341,6 +2365,14 @@ keep_going:						/* We will come back to here until there is
 						conn->status = CONNECTION_NEEDED;
 						goto keep_going;
 					}
+					else if (conn->read_write_host_index >= 0)
+					{
+						conn->addr_cur = conn->connhost[conn->read_write_host_index].addrlist;
+						conn->whichhost = conn->read_write_host_index;
+						conn->read_write_host_index = -1;
+						conn->status = CONNECTION_NEEDED;
+						goto keep_going;
+					}
 					goto error_return;
 				}
 
@@ -2978,10 +3010,12 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 */
 				if (conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					(strcmp(conn->target_session_attrs, "read-write") == 0 ||
+					 strcmp(conn->target_session_attrs, "prefer-read") == 0))
 				{
 					/*
 					 * We are yet to make a connection. Save all existing
@@ -3042,10 +3076,12 @@ keep_going:						/* We will come back to here until there is
 			}
 
 			/*
-			 * If a read-write connection is requested check for same.
+			 * If a read-write or prefer-read connection is requested check
+			 * for same.
 			 */
 			if (conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
+				(strcmp(conn->target_session_attrs, "read-write") == 0 ||
+				 strcmp(conn->target_session_attrs, "prefer-read") == 0))
 			{
 				if (!saveErrorMessage(conn, &savedMessage))
 					goto error_return;
@@ -3128,53 +3164,133 @@ keep_going:						/* We will come back to here until there is
 					val = PQgetvalue(res, 0, 0);
 					if (strncmp(val, "on", 2) == 0)
 					{
-						const char *displayed_host;
-						const char *displayed_port;
+						if (strcmp(conn->target_session_attrs, "read-write") == 0)
+						{
+							if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+								displayed_host = conn->connhost[conn->whichhost].hostaddr;
+							else
+								displayed_host = conn->connhost[conn->whichhost].host;
+							displayed_port = conn->connhost[conn->whichhost].port;
+							if (displayed_port == NULL || displayed_port[0] == '\0')
+								displayed_port = DEF_PGPORT_STR;
 
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
+							PQclear(res);
+							restoreErrorMessage(conn, &savedMessage);
 
-						PQclear(res);
-						restoreErrorMessage(conn, &savedMessage);
+							/* Not writable; close connection. */
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+							conn->status = CONNECTION_OK;
+							sendTerminateConn(conn);
+							pqDropConnection(conn, true);
 
-						/* Not writable; close connection. */
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-						pqDropConnection(conn, true);
+							/* Skip any remaining addresses for this host. */
+							conn->addr_cur = NULL;
+							if (conn->whichhost + 1 < conn->nconnhost)
+							{
+								conn->status = CONNECTION_NEEDED;
+								goto keep_going;
+							}
 
-						/* Skip any remaining addresses for this host. */
-						conn->addr_cur = NULL;
-						if (conn->whichhost + 1 < conn->nconnhost)
+							/* No more addresses to try. So we fail. */
+							goto error_return;
+						}
+						else	/* conn->target_session_attrs is prefer-read */
 						{
-							conn->status = CONNECTION_NEEDED;
+							PQclear(res);
+							termPQExpBuffer(&savedMessage);
+
+							/* We can release the address lists now. */
+							release_all_addrinfo(conn);
+
+							/*
+							 * Finish reading any remaining messages before
+							 * being considered as ready.
+							 */
+							conn->status = CONNECTION_CONSUME;
 							goto keep_going;
 						}
-
-						/* No more addresses to try. So we fail. */
-						goto error_return;
 					}
-					PQclear(res);
-					termPQExpBuffer(&savedMessage);
+					else		/* server support read-write */
+					{
+						if (strcmp(conn->target_session_attrs, "read-write") == 0)
+						{
+							PQclear(res);
+							termPQExpBuffer(&savedMessage);
 
-					/* We can release the address lists now. */
-					release_all_addrinfo(conn);
+							/* We can release the address lists now. */
+							release_all_addrinfo(conn);
 
-					/*
-					 * Finish reading any remaining messages before being
-					 * considered as ready.
-					 */
-					conn->status = CONNECTION_CONSUME;
-					goto keep_going;
+							/*
+							 * Finish reading any remaining messages before
+							 * being considered as ready.
+							 */
+							conn->status = CONNECTION_CONSUME;
+							goto keep_going;
+						}
+						else	/* conn->target_session_attrs is prefer-read */
+						{
+							/* is it the last connection? */
+							if (conn->whichhost + 1 < conn->nconnhost)
+							{
+								if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+									displayed_host = conn->connhost[conn->whichhost].hostaddr;
+								else
+									displayed_host = conn->connhost[conn->whichhost].host;
+								displayed_port = conn->connhost[conn->whichhost].port;
+								if (displayed_port == NULL || displayed_port[0] == '\0')
+									displayed_port = DEF_PGPORT_STR;
+
+								PQclear(res);
+								restoreErrorMessage(conn, &savedMessage);
+
+								/* Not read-only; close connection. */
+								appendPQExpBuffer(&conn->errorMessage,
+												  libpq_gettext("could not make a read-only "
+																"connection to server "
+																"\"%s:%s\"\n"),
+												  displayed_host, displayed_port);
+
+								/*
+								 * Connecting to a writable server, close it
+								 * and try to connect to another one.
+								 */
+								conn->status = CONNECTION_OK;
+								sendTerminateConn(conn);
+								pqDropConnection(conn, true);
+
+								/* Skip any remaining addresses for this host. */
+								conn->addr_cur = NULL;
+
+								conn->status = CONNECTION_NEEDED;
+
+								/* Record read-write host index, if not yet */
+								if (conn->read_write_host_index < 0)
+									conn->read_write_host_index = conn->whichhost;
+
+								goto keep_going;
+							}
+							else	/* No more host to connect, keep this
+									 * connection */
+							{
+								PQclear(res);
+								termPQExpBuffer(&savedMessage);
+
+								/* We can release the address lists now. */
+								release_all_addrinfo(conn);
+
+								/*
+								 * Finish reading any remaining messages
+								 * before being considered as ready.
+								 */
+								conn->status = CONNECTION_CONSUME;
+								goto keep_going;
+							}
+						}
+					}
 				}
 
 				/*
@@ -3393,6 +3509,8 @@ makeEmptyPGconn(void)
 		conn = NULL;
 	}
 
+	conn->read_write_host_index = -1;
+
 	return conn;
 }
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 9a586ff25a..39504999b3 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -362,7 +362,7 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/* Type of connection to make.  Possible values: any, read-write, perfer-read. */
 	char	   *target_session_attrs;
 
 	/* Optional file to write trace info to */
@@ -396,6 +396,7 @@ struct pg_conn
 	int			nconnhost;		/* # of possible hosts */
 	int			whichhost;		/* host we're currently considering */
 	pg_conn_host *connhost;		/* details about each possible host */
+	int 		read_write_host_index; /* index for first read-write host in connhost */
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index a0d3e8f357..e994306f28 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 28;
+use Test::More tests => 31;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.16.1.windows.4

From d0b94f2cb8c37e3a7f21c76ff362ca382347aced Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 7 Jun 2018 18:11:51 +1000
Subject: [PATCH] Allow taget-session-attrs to accept prefer-read option

With this new prefer-read option, the connection is preferred
to connect to a read-only server if available in the connection
string, otherwise connect to a read-write server.
---
 doc/src/sgml/libpq.sgml               |  13 ++-
 src/interfaces/libpq/fe-connect.c     | 209 ++++++++++++++++++++++++++--------
 src/interfaces/libpq/libpq-int.h      |   3 +-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 4 files changed, 190 insertions(+), 49 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index d67212b831..c89b4267f5 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1592,8 +1592,17 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         successful connection; if it returns <literal>on</literal>, the connection
         will be closed.  If multiple hosts were specified in the connection
         string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
+        attempt had failed.
+      </para>
+      <para>
+        If this parameter is set to <literal>prefer-read</literal>, connections
+        where <literal>SHOW transaction_read_only</literal> returns on are
+        preferred. If no such connections can be found, then a connection
+        that allows read-write transactions will be accepted.
+      </para>
+      <para>
+        The default value of this parameter,<literal>any</literal>, regards all
+        connections as acceptable.
       </para>
       </listitem>
     </varlistentry>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index a7e969d7c1..5a693abd56 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -327,7 +327,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1184,7 +1184,8 @@ connectOptions2(PGconn *conn)
 	if (conn->target_session_attrs)
 	{
 		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+			&& strcmp(conn->target_session_attrs, "read-write") != 0
+			&& strcmp(conn->target_session_attrs, "prefer-read") != 0)
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -2086,8 +2087,23 @@ keep_going:						/* We will come back to here until there is
 					{
 						if (++conn->whichhost >= conn->nconnhost)
 						{
-							conn->whichhost = 0;
-							break;
+							if (conn->read_write_host_index >= 0)
+							{
+								/*
+								 * Go to here means failed to connect to
+								 * read-only servers and now try connect to
+								 * read-write server again. Only under the
+								 * 'prefer-read' scenario will go to here.
+								 */
+								conn->addr_cur = conn->connhost[conn->read_write_host_index].addrlist;
+								conn->whichhost = conn->read_write_host_index;
+								conn->read_write_host_index = -2;
+							}
+							else
+							{
+								conn->whichhost = 0;
+								break;
+							}
 						}
 						conn->addr_cur =
 							conn->connhost[conn->whichhost].addrlist;
@@ -2112,6 +2128,14 @@ keep_going:						/* We will come back to here until there is
 							conn->addr_cur = addr_cur->ai_next;
 							continue;
 						}
+						else if (conn->read_write_host_index >= 0)
+						{
+							conn->addr_cur = conn->connhost[conn->read_write_host_index].addrlist;
+							conn->whichhost = conn->read_write_host_index;
+							conn->read_write_host_index = -2;
+							continue;
+						}
+
 						appendPQExpBuffer(&conn->errorMessage,
 										  libpq_gettext("could not create socket: %s\n"),
 										  SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
@@ -2341,6 +2365,14 @@ keep_going:						/* We will come back to here until there is
 						conn->status = CONNECTION_NEEDED;
 						goto keep_going;
 					}
+					else if (conn->read_write_host_index >= 0)
+					{
+						conn->addr_cur = conn->connhost[conn->read_write_host_index].addrlist;
+						conn->whichhost = conn->read_write_host_index;
+						conn->read_write_host_index = -2;
+						conn->status = CONNECTION_NEEDED;
+						goto keep_going;
+					}
 					goto error_return;
 				}
 
@@ -2978,10 +3010,12 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 */
 				if (conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					(strcmp(conn->target_session_attrs, "read-write") == 0 ||
+					 strcmp(conn->target_session_attrs, "prefer-read") == 0))
 				{
 					/*
 					 * We are yet to make a connection. Save all existing
@@ -3042,10 +3076,12 @@ keep_going:						/* We will come back to here until there is
 			}
 
 			/*
-			 * If a read-write connection is requested check for same.
+			 * If a read-write or prefer-read connection is requested check
+			 * for same.
 			 */
 			if (conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
+				(strcmp(conn->target_session_attrs, "read-write") == 0 ||
+				 strcmp(conn->target_session_attrs, "prefer-read") == 0))
 			{
 				if (!saveErrorMessage(conn, &savedMessage))
 					goto error_return;
@@ -3128,53 +3164,134 @@ keep_going:						/* We will come back to here until there is
 					val = PQgetvalue(res, 0, 0);
 					if (strncmp(val, "on", 2) == 0)
 					{
-						const char *displayed_host;
-						const char *displayed_port;
+						if (strcmp(conn->target_session_attrs, "read-write") == 0)
+						{
+							if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+								displayed_host = conn->connhost[conn->whichhost].hostaddr;
+							else
+								displayed_host = conn->connhost[conn->whichhost].host;
+							displayed_port = conn->connhost[conn->whichhost].port;
+							if (displayed_port == NULL || displayed_port[0] == '\0')
+								displayed_port = DEF_PGPORT_STR;
 
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
+							PQclear(res);
+							restoreErrorMessage(conn, &savedMessage);
 
-						PQclear(res);
-						restoreErrorMessage(conn, &savedMessage);
+							/* Not writable; close connection. */
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+							conn->status = CONNECTION_OK;
+							sendTerminateConn(conn);
+							pqDropConnection(conn, true);
 
-						/* Not writable; close connection. */
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-						pqDropConnection(conn, true);
+							/* Skip any remaining addresses for this host. */
+							conn->addr_cur = NULL;
+							if (conn->whichhost + 1 < conn->nconnhost)
+							{
+								conn->status = CONNECTION_NEEDED;
+								goto keep_going;
+							}
 
-						/* Skip any remaining addresses for this host. */
-						conn->addr_cur = NULL;
-						if (conn->whichhost + 1 < conn->nconnhost)
+							/* No more addresses to try. So we fail. */
+							goto error_return;
+						}
+						else	/* conn->target_session_attrs is prefer-read */
 						{
-							conn->status = CONNECTION_NEEDED;
+							PQclear(res);
+							termPQExpBuffer(&savedMessage);
+
+							/* We can release the address lists now. */
+							release_all_addrinfo(conn);
+
+							/*
+							 * Finish reading any remaining messages before
+							 * being considered as ready.
+							 */
+							conn->status = CONNECTION_CONSUME;
 							goto keep_going;
 						}
-
-						/* No more addresses to try. So we fail. */
-						goto error_return;
 					}
-					PQclear(res);
-					termPQExpBuffer(&savedMessage);
+					else		/* server support read-write */
+					{
+						if (strcmp(conn->target_session_attrs, "read-write") == 0)
+						{
+							PQclear(res);
+							termPQExpBuffer(&savedMessage);
 
-					/* We can release the address lists now. */
-					release_all_addrinfo(conn);
+							/* We can release the address lists now. */
+							release_all_addrinfo(conn);
 
-					/*
-					 * Finish reading any remaining messages before being
-					 * considered as ready.
-					 */
-					conn->status = CONNECTION_CONSUME;
-					goto keep_going;
+							/*
+							 * Finish reading any remaining messages before
+							 * being considered as ready.
+							 */
+							conn->status = CONNECTION_CONSUME;
+							goto keep_going;
+						}
+						else	/* conn->target_session_attrs is prefer-read */
+						{
+							/* is it the last connection? */
+							if ((conn->whichhost + 1 < conn->nconnhost) &&
+								(conn->read_write_host_index != -2))
+							{
+								if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+									displayed_host = conn->connhost[conn->whichhost].hostaddr;
+								else
+									displayed_host = conn->connhost[conn->whichhost].host;
+								displayed_port = conn->connhost[conn->whichhost].port;
+								if (displayed_port == NULL || displayed_port[0] == '\0')
+									displayed_port = DEF_PGPORT_STR;
+
+								PQclear(res);
+								restoreErrorMessage(conn, &savedMessage);
+
+								/* Not read-only; close connection. */
+								appendPQExpBuffer(&conn->errorMessage,
+												  libpq_gettext("could not make a read-only "
+																"connection to server "
+																"\"%s:%s\"\n"),
+												  displayed_host, displayed_port);
+
+								/*
+								 * Connecting to a writable server, close it
+								 * and try to connect to another one.
+								 */
+								conn->status = CONNECTION_OK;
+								sendTerminateConn(conn);
+								pqDropConnection(conn, true);
+
+								/* Skip any remaining addresses for this host. */
+								conn->addr_cur = NULL;
+
+								conn->status = CONNECTION_NEEDED;
+
+								/* Record read-write host index, if not yet */
+								if (conn->read_write_host_index == -1)
+									conn->read_write_host_index = conn->whichhost;
+
+								goto keep_going;
+							}
+							else	/* No more host to connect, keep this
+									 * connection */
+							{
+								PQclear(res);
+								termPQExpBuffer(&savedMessage);
+
+								/* We can release the address lists now. */
+								release_all_addrinfo(conn);
+
+								/*
+								 * Finish reading any remaining messages
+								 * before being considered as ready.
+								 */
+								conn->status = CONNECTION_CONSUME;
+								goto keep_going;
+							}
+						}
+					}
 				}
 
 				/*
@@ -3393,6 +3510,8 @@ makeEmptyPGconn(void)
 		conn = NULL;
 	}
 
+	conn->read_write_host_index = -1;
+
 	return conn;
 }
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 9a586ff25a..39504999b3 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -362,7 +362,7 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/* Type of connection to make.  Possible values: any, read-write, perfer-read. */
 	char	   *target_session_attrs;
 
 	/* Optional file to write trace info to */
@@ -396,6 +396,7 @@ struct pg_conn
 	int			nconnhost;		/* # of possible hosts */
 	int			whichhost;		/* host we're currently considering */
 	pg_conn_host *connhost;		/* details about each possible host */
+	int 		read_write_host_index; /* index for first read-write host in connhost */
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index a0d3e8f357..e994306f28 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 28;
+use Test::More tests => 31;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.16.1.windows.4

From d99b0456390573cb2df3324064e8d87c05cce327 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 7 Jun 2018 18:11:51 +1000
Subject: [PATCH] Allow taget-session-attrs to accept prefer-read option

With this new prefer-read option, the connection is preferred
to connect to a read-only server if available in the connection
string, otherwise connect to a read-write server.
---
 doc/src/sgml/libpq.sgml               |  13 ++-
 src/interfaces/libpq/fe-connect.c     | 146 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   2 +
 src/interfaces/libpq/libpq-int.h      |   3 +-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 152 insertions(+), 26 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 06d909e804..b70cf04a61 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1584,8 +1584,17 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         successful connection; if it returns <literal>on</literal>, the connection
         will be closed.  If multiple hosts were specified in the connection
         string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
+        attempt had failed.
+      </para>
+      <para>
+        If this parameter is set to <literal>prefer-read</literal>, connections
+        where <literal>SHOW transaction_read_only</literal> returns <literal>on</literal>
+        are preferred. If no such connections can be found, then a connection
+        that allows read-write transactions will be accepted.
+      </para>
+      <para>
+        The default value of this parameter,<literal>any</literal>, regards all
+        connections as acceptable.
       </para>
       </listitem>
     </varlistentry>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index d001bc513d..93d9abd3fb 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1240,7 +1240,8 @@ connectOptions2(PGconn *conn)
 	if (conn->target_session_attrs)
 	{
 		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+			&& strcmp(conn->target_session_attrs, "read-write") != 0
+			&& strcmp(conn->target_session_attrs, "prefer-read") != 0)
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -2083,6 +2084,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_SSL_STARTUP:
 		case CONNECTION_NEEDED:
 		case CONNECTION_CHECK_WRITABLE:
+		case CONNECTION_CHECK_READONLY:
 		case CONNECTION_CONSUME:
 			break;
 
@@ -2123,13 +2125,28 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Go to here means failed to connect to
+				 * read-only servers and now try connect to
+				 * read-write server again. Only under the
+				 * 'prefer-read' scenario will go to here.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is already
+				 * set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -2317,6 +2334,7 @@ keep_going:						/* We will come back to here until there is
 							conn->try_next_addr = true;
 							goto keep_going;
 						}
+
 						appendPQExpBuffer(&conn->errorMessage,
 										  libpq_gettext("could not create socket: %s\n"),
 										  SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
@@ -3158,7 +3176,8 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required,
+				 * see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3166,7 +3185,8 @@ keep_going:						/* We will come back to here until there is
 				 */
 				if (conn->sversion >= 70400 &&
 					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					(strcmp(conn->target_session_attrs, "read-write") == 0 ||
+					 strcmp(conn->target_session_attrs, "prefer-read") == 0))
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3185,11 +3205,40 @@ keep_going:						/* We will come back to here until there is
 						restoreErrorMessage(conn, &savedMessage);
 						goto error_return;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
+
+					if (strcmp(conn->target_session_attrs, "read-write") == 0)
+						conn->status = CONNECTION_CHECK_WRITABLE;
+					else
+						conn->status = CONNECTION_CHECK_READONLY;
+
 					restoreErrorMessage(conn, &savedMessage);
 					return PGRES_POLLING_READING;
 				}
 
+				/*
+				 * Requested type is prefer-read then record this connection index
+				 * and try the other before considering it later
+				 */
+				if ((conn->target_session_attrs != NULL) &&
+						(strcmp(conn->target_session_attrs, "prefer-read") == 0) &&
+						(conn->read_write_host_index != -2))
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record it */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
+				}
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3226,9 +3275,9 @@ keep_going:						/* We will come back to here until there is
 			}
 
 			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
+			 * If a read-write or prefer-read connection is required,
+			 * see if we have one. (This should match the stanza in the
+			 * CONNECTION_AUTH_OK case above.)
 			 *
 			 * Servers before 7.4 lack the transaction_read_only GUC, but by
 			 * the same token they don't have any read-only mode, so we may
@@ -3236,7 +3285,8 @@ keep_going:						/* We will come back to here until there is
 			 */
 			if (conn->sversion >= 70400 &&
 				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
+				((strcmp(conn->target_session_attrs, "read-write") == 0) ||
+				 (strcmp(conn->target_session_attrs, "prefer-read") == 0)))
 			{
 				if (!saveErrorMessage(conn, &savedMessage))
 					goto error_return;
@@ -3248,11 +3298,40 @@ keep_going:						/* We will come back to here until there is
 					restoreErrorMessage(conn, &savedMessage);
 					goto error_return;
 				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
+
+				if (strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->status = CONNECTION_CHECK_WRITABLE;
+				else
+					conn->status = CONNECTION_CHECK_READONLY;
+
 				restoreErrorMessage(conn, &savedMessage);
 				return PGRES_POLLING_READING;
 			}
 
+			/*
+			 * Requested type is prefer-read then record this connection index
+			 * and try the other before considering it later
+			 */
+			if ((conn->target_session_attrs != NULL) &&
+					(strcmp(conn->target_session_attrs, "prefer-read") == 0) &&
+					(conn->read_write_host_index != -2))
+			{
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Record it */
+				if (conn->read_write_host_index == -1)
+					conn->read_write_host_index = conn->whichhost;
+
+				/*
+				 * Try next host if any, but we don't want to consider
+				 * additional addresses for this host.
+				 */
+				conn->try_next_host = true;
+				goto keep_going;
+			}
+
 			/* We can release the address list now. */
 			release_conn_addrinfo(conn);
 
@@ -3291,13 +3370,16 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 		case CONNECTION_CHECK_WRITABLE:
+		case CONNECTION_CHECK_READONLY:
 			{
+				ConnStatusType oldstatus;
 				const char *displayed_host;
 				const char *displayed_port;
 
 				if (!saveErrorMessage(conn, &savedMessage))
 					goto error_return;
 
+				oldstatus = conn->status;
 				conn->status = CONNECTION_OK;
 				if (!PQconsumeInput(conn))
 				{
@@ -3307,7 +3389,7 @@ keep_going:						/* We will come back to here until there is
 
 				if (PQisBusy(conn))
 				{
-					conn->status = CONNECTION_CHECK_WRITABLE;
+					conn->status = oldstatus;
 					restoreErrorMessage(conn, &savedMessage);
 					return PGRES_POLLING_READING;
 				}
@@ -3319,11 +3401,24 @@ keep_going:						/* We will come back to here until there is
 					char	   *val;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+
+					/*
+					 * Server is read-only and requested mode is read-write, ignore it.
+					 * Server is read-write and requested mode is prefer-read, record
+					 * it for the first time and try to consume in the next scan (it means
+					 * no read-only server is found in the first scan).
+					 */
+					if (((strncmp(val, "on", 2) == 0) &&
+							(oldstatus == CONNECTION_CHECK_WRITABLE)) ||
+						((strncmp(val, "off", 3) == 0) &&
+							(oldstatus == CONNECTION_CHECK_READONLY) &&
+							(conn->read_write_host_index != -2)))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
+						const char *type = (oldstatus == CONNECTION_CHECK_READONLY) ?
+											"read-only" : "writable";
 
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
@@ -3338,15 +3433,20 @@ keep_going:						/* We will come back to here until there is
 							displayed_port = DEF_PGPORT_STR;
 
 						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
+										  libpq_gettext("could not make a %s "
 														"connection to server "
 														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+										  type, displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if ((oldstatus == CONNECTION_CHECK_READONLY) &&
+								(conn->read_write_host_index == -1))
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3355,7 +3455,7 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3568,6 +3668,8 @@ makeEmptyPGconn(void)
 		conn = NULL;
 	}
 
+	conn->read_write_host_index = -1;
+
 	return conn;
 }
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 52bd5d2cd8..582f83bb0e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -65,6 +65,8 @@ typedef enum
 	CONNECTION_NEEDED,			/* Internal state: connect() needed */
 	CONNECTION_CHECK_WRITABLE,	/* Check if we could make a writable
 								 * connection. */
+	CONNECTION_CHECK_READONLY,	/* Check if we could make a read-only
+								 * connection. */
 	CONNECTION_CONSUME			/* Wait for any pending message and consume
 								 * them. */
 } ConnStatusType;
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 975ab33d02..a4716af654 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -363,7 +363,7 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/* Type of connection to make.  Possible values: any, read-write, perfer-read. */
 	char	   *target_session_attrs;
 
 	/* Optional file to write trace info to */
@@ -397,6 +397,7 @@ struct pg_conn
 	int			nconnhost;		/* # of hosts named in conn string */
 	int			whichhost;		/* host we're currently trying/connected to */
 	pg_conn_host *connhost;		/* details about each named host */
+	int 		read_write_host_index; /* index for first read-write host in connhost */
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 8dff5fc720..8a6edd6867 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.18.0.windows.1

From d513e1748677048fe7f4e18419d092247a211c3e Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 7 Jun 2018 18:11:51 +1000
Subject: [PATCH] Allow taget-session-attrs to accept prefer-read option

With this new prefer-read option, the connection is preferred
to connect to a read-only server if available in the connection
string, otherwise connect to a first read-write server in the
connection string.
---
 doc/src/sgml/libpq.sgml               |  13 ++-
 src/interfaces/libpq/fe-connect.c     | 150 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   2 +
 src/interfaces/libpq/libpq-int.h      |  10 +-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 163 insertions(+), 26 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 601091c570..d28dedd942 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1584,8 +1584,17 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         successful connection; if it returns <literal>on</literal>, the connection
         will be closed.  If multiple hosts were specified in the connection
         string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
+        attempt had failed.
+      </para>
+      <para>
+        If this parameter is set to <literal>prefer-read</literal>, connections
+        where <literal>SHOW transaction_read_only</literal> returns <literal>on</literal>
+        are preferred. If no such connections can be found, then a connection
+        that allows read-write transactions will be accepted.
+      </para>
+      <para>
+        The default value of this parameter,<literal>any</literal>, regards all
+        connections as acceptable.
       </para>
       </listitem>
     </varlistentry>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index d001bc513d..ed20226c13 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1240,7 +1240,8 @@ connectOptions2(PGconn *conn)
 	if (conn->target_session_attrs)
 	{
 		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+			&& strcmp(conn->target_session_attrs, "read-write") != 0
+			&& strcmp(conn->target_session_attrs, "prefer-read") != 0)
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -2083,6 +2084,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_SSL_STARTUP:
 		case CONNECTION_NEEDED:
 		case CONNECTION_CHECK_WRITABLE:
+		case CONNECTION_CHECK_READONLY:
 		case CONNECTION_CONSUME:
 			break;
 
@@ -2123,13 +2125,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is already
+				 * set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -2317,6 +2337,7 @@ keep_going:						/* We will come back to here until there is
 							conn->try_next_addr = true;
 							goto keep_going;
 						}
+
 						appendPQExpBuffer(&conn->errorMessage,
 										  libpq_gettext("could not create socket: %s\n"),
 										  SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
@@ -3158,7 +3179,8 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required,
+				 * see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3166,7 +3188,8 @@ keep_going:						/* We will come back to here until there is
 				 */
 				if (conn->sversion >= 70400 &&
 					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					(strcmp(conn->target_session_attrs, "read-write") == 0 ||
+					 strcmp(conn->target_session_attrs, "prefer-read") == 0))
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3185,11 +3208,40 @@ keep_going:						/* We will come back to here until there is
 						restoreErrorMessage(conn, &savedMessage);
 						goto error_return;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
+
+					if (strcmp(conn->target_session_attrs, "read-write") == 0)
+						conn->status = CONNECTION_CHECK_WRITABLE;
+					else
+						conn->status = CONNECTION_CHECK_READONLY;
+
 					restoreErrorMessage(conn, &savedMessage);
 					return PGRES_POLLING_READING;
 				}
 
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if ((conn->target_session_attrs != NULL) &&
+						(strcmp(conn->target_session_attrs, "prefer-read") == 0) &&
+						(conn->read_write_host_index != -2))
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
+				}
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3226,9 +3278,9 @@ keep_going:						/* We will come back to here until there is
 			}
 
 			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
+			 * If a read-write or prefer-read connection is required,
+			 * see if we have one. (This should match the stanza in the
+			 * CONNECTION_AUTH_OK case above.)
 			 *
 			 * Servers before 7.4 lack the transaction_read_only GUC, but by
 			 * the same token they don't have any read-only mode, so we may
@@ -3236,7 +3288,8 @@ keep_going:						/* We will come back to here until there is
 			 */
 			if (conn->sversion >= 70400 &&
 				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
+				((strcmp(conn->target_session_attrs, "read-write") == 0) ||
+				 (strcmp(conn->target_session_attrs, "prefer-read") == 0)))
 			{
 				if (!saveErrorMessage(conn, &savedMessage))
 					goto error_return;
@@ -3248,11 +3301,40 @@ keep_going:						/* We will come back to here until there is
 					restoreErrorMessage(conn, &savedMessage);
 					goto error_return;
 				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
+
+				if (strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->status = CONNECTION_CHECK_WRITABLE;
+				else
+					conn->status = CONNECTION_CHECK_READONLY;
+
 				restoreErrorMessage(conn, &savedMessage);
 				return PGRES_POLLING_READING;
 			}
 
+			/*
+			 * Requested type is prefer-read, then record this host index
+			 * and try the other before considering it later
+			 */
+			if ((conn->target_session_attrs != NULL) &&
+					(strcmp(conn->target_session_attrs, "prefer-read") == 0) &&
+					(conn->read_write_host_index != -2))
+			{
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Record read-write host index */
+				if (conn->read_write_host_index == -1)
+					conn->read_write_host_index = conn->whichhost;
+
+				/*
+				 * Try next host if any, but we don't want to consider
+				 * additional addresses for this host.
+				 */
+				conn->try_next_host = true;
+				goto keep_going;
+			}
+
 			/* We can release the address list now. */
 			release_conn_addrinfo(conn);
 
@@ -3291,13 +3373,16 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 		case CONNECTION_CHECK_WRITABLE:
+		case CONNECTION_CHECK_READONLY:
 			{
+				ConnStatusType oldstatus;
 				const char *displayed_host;
 				const char *displayed_port;
 
 				if (!saveErrorMessage(conn, &savedMessage))
 					goto error_return;
 
+				oldstatus = conn->status;
 				conn->status = CONNECTION_OK;
 				if (!PQconsumeInput(conn))
 				{
@@ -3307,7 +3392,7 @@ keep_going:						/* We will come back to here until there is
 
 				if (PQisBusy(conn))
 				{
-					conn->status = CONNECTION_CHECK_WRITABLE;
+					conn->status = oldstatus;
 					restoreErrorMessage(conn, &savedMessage);
 					return PGRES_POLLING_READING;
 				}
@@ -3319,11 +3404,24 @@ keep_going:						/* We will come back to here until there is
 					char	   *val;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+
+					/*
+					 * Server is read-only and requested mode is read-write, ignore it.
+					 * Server is read-write and requested mode is prefer-read, record
+					 * it for the first time and try to consume in the next scan (it means
+					 * no read-only server is found in the first scan).
+					 */
+					if (((strncmp(val, "on", 2) == 0) &&
+							(oldstatus == CONNECTION_CHECK_WRITABLE)) ||
+						((strncmp(val, "off", 3) == 0) &&
+							(oldstatus == CONNECTION_CHECK_READONLY) &&
+							(conn->read_write_host_index != -2)))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
+						const char *type = (oldstatus == CONNECTION_CHECK_READONLY) ?
+											"read-only" : "writable";
 
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
@@ -3338,15 +3436,20 @@ keep_going:						/* We will come back to here until there is
 							displayed_port = DEF_PGPORT_STR;
 
 						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
+										  libpq_gettext("could not make a %s "
 														"connection to server "
 														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+										  type, displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if ((oldstatus == CONNECTION_CHECK_READONLY) &&
+								(conn->read_write_host_index == -1))
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3355,7 +3458,7 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3568,6 +3671,9 @@ makeEmptyPGconn(void)
 		conn = NULL;
 	}
 
+	/* Initial value */
+	conn->read_write_host_index = -1;
+
 	return conn;
 }
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 52bd5d2cd8..582f83bb0e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -65,6 +65,8 @@ typedef enum
 	CONNECTION_NEEDED,			/* Internal state: connect() needed */
 	CONNECTION_CHECK_WRITABLE,	/* Check if we could make a writable
 								 * connection. */
+	CONNECTION_CHECK_READONLY,	/* Check if we could make a read-only
+								 * connection. */
 	CONNECTION_CONSUME			/* Wait for any pending message and consume
 								 * them. */
 } ConnStatusType;
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 975ab33d02..e62378cdea 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -363,7 +363,7 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/* Type of connection to make.  Possible values: any, read-write, perfer-read. */
 	char	   *target_session_attrs;
 
 	/* Optional file to write trace info to */
@@ -398,6 +398,14 @@ struct pg_conn
 	int			whichhost;		/* host we're currently trying/connected to */
 	pg_conn_host *connhost;		/* details about each named host */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write
+	 * host, -2 during the second attempt of connection to avoid recursion.
+	 */
+	int 		read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 8dff5fc720..8a6edd6867 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.18.0.windows.1

From 9264fc5bb2188043bcd19d0e549bf1e55f685d38 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Fri, 22 Feb 2019 00:09:02 +1100
Subject: [PATCH 2/4] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 10 ++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index fa157bd2dc..e03d78d3f8 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1239,8 +1239,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3229,8 +3232,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type == SESSION_TYPE_READ_WRITE)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 1961161b35..15bb82a885 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -71,6 +71,12 @@ typedef enum
 								 * them. */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+} TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 4a93d8edbc..43aa6b5f30 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,6 +365,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.20.1.windows.1

From 8444117409b1d4326f3f8014aa29069a4493fd1f Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Fri, 22 Feb 2019 00:22:43 +1100
Subject: [PATCH 4/4] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  15 ++-
 src/interfaces/libpq/fe-connect.c     | 126 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  10 +-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 143 insertions(+), 25 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 5c29beef51..d4bddef6cf 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1585,8 +1585,19 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         returns <literal>on</literal>, the connection will be closed.
         If multiple hosts were specified in the connection string, any 
         remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
+        attempt had failed.
+      </para>
+      
+      <para>
+        If this parameter is set to <literal>prefer-read</literal>, connections
+        where <literal>SHOW transaction_read_only</literal> returns <literal>on</literal>
+        are preferred. If no such connections can be found, then a connection
+        that allows read-write transactions will be accepted.
+      </para>
+
+      <para>    
+    The default value of this parameter is <literal>any</literal>,
+    regards all connections as acceptable.
       </para>
       </listitem>
     </varlistentry>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 25a153f48c..6943674067 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1243,6 +1243,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2137,13 +2139,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is already
+				 * set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -2347,6 +2367,7 @@ keep_going:						/* We will come back to here until there is
 							conn->try_next_addr = true;
 							goto keep_going;
 						}
+
 						appendPQExpBuffer(&conn->errorMessage,
 										  libpq_gettext("could not create socket: %s\n"),
 										  SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
@@ -3225,14 +3246,16 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required,
+				 * see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3253,15 +3276,23 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only
+								&& (conn->requested_session_type == SESSION_TYPE_READ_WRITE)) ||
+							(!conn->transaction_read_only
+								&& (conn->requested_session_type == SESSION_TYPE_PREFER_READ)
+								&& (conn->read_write_host_index != -2)))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
+						const char *type = (conn->requested_session_type == SESSION_TYPE_PREFER_READ) ?
+											"read-only" : "writable";
 
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
@@ -3273,15 +3304,19 @@ keep_going:						/* We will come back to here until there is
 							displayed_port = DEF_PGPORT_STR;
 
 						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
+										  libpq_gettext("could not make a %s "
 														"connection to server "
 														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+										  type, displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3289,6 +3324,39 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+					else /* obtained the requested type, consume it */
+					{
+						/* We can release the address list now. */
+						release_conn_addrinfo(conn);
+
+						/* We are open for business! */
+						conn->status = CONNECTION_OK;
+						return PGRES_POLLING_OK;
+					}
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if ((conn->target_session_attrs != NULL) &&
+					   (conn->requested_session_type == SESSION_TYPE_PREFER_READ) &&
+					   (conn->read_write_host_index != -2))
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
 				/* We can release the address list now. */
@@ -3358,11 +3426,22 @@ keep_going:						/* We will come back to here until there is
 					char	   *val;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+
+					/*
+					 * Server is read-only and requested mode is read-write, ignore it.
+					 * Server is read-write and requested mode is prefer-read, record
+					 * it for the first time and try to consume in the next scan (it means
+					 * no read-only server is found in the first scan).
+					 */
+					if (((strncmp(val, "on", 2) == 0) &&
+							(conn->requested_session_type == SESSION_TYPE_READ_WRITE)) ||
+						((strncmp(val, "off", 3) == 0) &&
+							(conn->requested_session_type == SESSION_TYPE_PREFER_READ) &&
+							(conn->read_write_host_index != -2)))
 					{
-						/* Not writable; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
+						/* Not a requested type; fail this connection. */
+						const char *type = (conn->requested_session_type == SESSION_TYPE_PREFER_READ) ?
+											"read-only" : "writable";
 
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
@@ -3377,15 +3456,19 @@ keep_going:						/* We will come back to here until there is
 							displayed_port = DEF_PGPORT_STR;
 
 						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
+										  libpq_gettext("could not make a %s "
 														"connection to server "
 														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+										  type, displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3394,7 +3477,7 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3608,6 +3691,9 @@ makeEmptyPGconn(void)
 		conn = NULL;
 	}
 
+	/* Initial value */
+	conn->read_write_host_index = -1;
+
 	return conn;
 }
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 15bb82a885..a7de100c3b 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 } TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index b0ac98b90d..1878598633 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -363,7 +363,7 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/* Type of connection to make.  Possible values: any, read-write, perfer-read. */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -400,6 +400,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write
+	 * host, -2 during the second attempt of connection to avoid recursion.
+	 */
+	int 		read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index beb45551a2..0e398136a5 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From a0d0f95fa4115df3a302a44285234f96067d2dd6 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 21 Feb 2019 23:11:55 +1100
Subject: [PATCH 1/4] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the transaction_readonly to find out whether
the server is read-write or not is restuctured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches
---
 src/interfaces/libpq/fe-connect.c | 99 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  2 +
 2 files changed, 39 insertions(+), 62 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index f29202db5f..fa157bd2dc 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3184,6 +3184,43 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_SETENV:
+			{
+
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
+				conn->status = CONNECTION_OK;
+
+				switch (pqSetenvPoll(conn))
+				{
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
+				}
+			}
+
+			/* Intentional fall through */
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3225,68 +3262,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
-			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
-				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
-				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
-				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
-			}
-
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 97bc98b1f3..1961161b35 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -65,6 +65,8 @@ typedef enum
 	CONNECTION_NEEDED,			/* Internal state: connect() needed */
 	CONNECTION_CHECK_WRITABLE,	/* Check if we could make a writable
 								 * connection. */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target
+								 * connection */
 	CONNECTION_CONSUME			/* Wait for any pending message and consume
 								 * them. */
 } ConnStatusType;
-- 
2.20.1.windows.1

From 4b2a5db17bfca262d5c7201dab248769a002d4e1 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Fri, 22 Feb 2019 00:12:37 +1100
Subject: [PATCH 3/4] Make transaction_read_only as GUC_REPORT varaible

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 15 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 28 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c1d1b6b2db..5c29beef51 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1581,9 +1581,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         connection in which read-write transactions are accepted by default
         is considered acceptable.  The query
         <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
+        successful connection if the server is prior to version 12; if it
+        returns <literal>on</literal>, the connection will be closed.
+        If multiple hosts were specified in the connection string, any 
+        remaining servers will be tried just as if the connection
         attempt had failed.  The default value of this parameter,
         <literal>any</literal>, regards all connections as acceptable.
       </para>
@@ -1951,14 +1952,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>, 
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index d66b860cbd..6b22dfe47a 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 156d147c85..cf62cf8699 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1506,7 +1506,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index e03d78d3f8..25a153f48c 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3234,26 +3234,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type == SESSION_TYPE_READ_WRITE)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3537,6 +3572,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index ac969e7b3f..5adfc36171 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1033,7 +1033,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1087,6 +1087,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp (name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 43aa6b5f30..b0ac98b90d 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -428,6 +428,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* session_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From 60a2b45e081e0916d4a3199e1d93eed2a6a5d71c Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 16:12:24 +1100
Subject: [PATCH 3/5] Make transaction_read_only as GUC_REPORT varaible

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index ac78524924..7b9d219bde 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1594,8 +1594,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, means server doesn't support read-write transactions.
+        But for servers version 12 or greater uses the <varname>transaction_read_only</varname>
+        GUC that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -1961,14 +1963,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index d66b860cbd..f3357b5c59 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 156d147c85..cf62cf8699 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1506,7 +1506,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 9932dccec5..718a981ed6 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3234,26 +3234,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type == SESSION_TYPE_READ_WRITE)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3534,6 +3569,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index ac969e7b3f..99dd8b1c9c 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1033,7 +1033,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1087,6 +1087,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 43aa6b5f30..b0ac98b90d 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -428,6 +428,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* session_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From fc8596034bb34727eb8198988d69c0a17e795c3c Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH 2/5] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 09e010de7e..9932dccec5 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1239,8 +1239,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3229,8 +3232,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type == SESSION_TYPE_READ_WRITE)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3536,6 +3538,8 @@ makeEmptyPGconn(void)
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 50cfe266c6..6961d7ce8e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -70,6 +70,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 4a93d8edbc..43aa6b5f30 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,6 +365,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.20.1.windows.1

From 463e566cfaa8d40a0d674fb4caab1b2cad05cad3 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 16:29:29 +1100
Subject: [PATCH 5/5] New read-only target_session_attrs type

With this read-only option type, application can connect to
connecting to a read-only server in the list of hosts, in case
if there is any read-only servers available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  2 +-
 src/interfaces/libpq/fe-connect.c     | 28 ++++++++++++++++++---------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 14 +++++++++++++-
 5 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7918e398c7..f7331fba32 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1578,7 +1578,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>, 
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 55bf9f1522..0f89af0787 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1245,6 +1245,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3254,7 +3256,8 @@ keep_going:						/* We will come back to here until there is
 				 */
 				if (conn->sversion >= 70400 &&
 					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
-					 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3284,8 +3287,9 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							  conn->read_write_host_index != -2))
+							  ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+								conn->read_write_host_index != -2) ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3319,6 +3323,7 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (!conn->transaction_read_only &&
+							conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
 							conn->read_write_host_index == -1)
 							conn->read_write_host_index = conn->whichhost;
 
@@ -3344,15 +3349,17 @@ keep_going:						/* We will come back to here until there is
 				 * Requested type is prefer-read, then record this host index
 				 * and try the other before considering it later
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					 conn->read_write_host_index != -2) ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3443,8 +3450,9 @@ keep_going:						/* We will come back to here until there is
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						 conn->read_write_host_index != -2))
+						 ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						   conn->read_write_host_index != -2) ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						PQclear(res);
@@ -3477,7 +3485,9 @@ keep_going:						/* We will come back to here until there is
 						sendTerminateConn(conn);
 
 						/* Record read-write host index */
-						if (!readonly_server && conn->read_write_host_index == -1)
+						if (!readonly_server &&
+							conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
 							conn->read_write_host_index = conn->whichhost;
 
 						/*
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 4b0fc80df2..5d0b885dae 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index d6c482fd0b..8690f86956 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 0e398136a5..0d6f279586 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 29;
+use Test::More tests => 32;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -129,6 +129,18 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
+# Connection should fail in "read-only" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"read-only", 1);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From 47cfcb9c574c1d2d3c33068f1ff3dc09ee281cac Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 21 Feb 2019 23:11:55 +1100
Subject: [PATCH 1/5] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the transaction_readonly to find out whether
the server is read-write or not is restuctured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches
---
 doc/src/sgml/libpq.sgml           | 26 +++++---
 src/interfaces/libpq/fe-connect.c | 99 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  3 +-
 3 files changed, 57 insertions(+), 71 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c1d1b6b2db..ac78524924 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1576,17 +1576,27 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
      <varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
       <term><literal>target_session_attrs</literal></term>
       <listitem>
+       <para>
+        The supported options for this parameter are, <literal>any</literal> and
+        <literal>read-write</literal>. The default value of this parameter,
+        <literal>any</literal>, regards all connections as acceptable.
+        If multiple hosts were specified in the connection string, based on the
+        specified value, any remaining servers will be tried before confirming
+        succesful connection or failure.
+       </para>
+
        <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        To find out whether the server supports read-write transactions are not,
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection; if it returns <literal>on</literal>, means server
+        doesn't support read-write transactions.
+       </para>
       </listitem>
     </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index c96a52bb1b..09e010de7e 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3184,6 +3184,43 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_SETENV:
+			{
+
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
+				conn->status = CONNECTION_OK;
+
+				switch (pqSetenvPoll(conn))
+				{
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
+				}
+			}
+
+			/* Intentional fall through */
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3225,68 +3262,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
-			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
-				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
-				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
-				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
-			}
-
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 97bc98b1f3..50cfe266c6 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -65,8 +65,9 @@ typedef enum
 	CONNECTION_NEEDED,			/* Internal state: connect() needed */
 	CONNECTION_CHECK_WRITABLE,	/* Check if we could make a writable
 								 * connection. */
-	CONNECTION_CONSUME			/* Wait for any pending message and consume
+	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
+	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
 typedef enum
-- 
2.20.1.windows.1

From a7cdbcc3681659e036a7db1821a097a07f5e361e Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 16:16:25 +1100
Subject: [PATCH 4/5] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 146 +++++++++++++++++++++-----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 163 insertions(+), 34 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7b9d219bde..7918e398c7 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1577,12 +1577,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>, 
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1591,6 +1591,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1600,7 +1607,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         GUC that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 718a981ed6..55bf9f1522 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1243,6 +1243,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2137,13 +2139,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is already
+				 * set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3225,14 +3245,16 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3253,13 +3275,19 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							  conn->read_write_host_index != -2))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
@@ -3272,16 +3300,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (!conn->transaction_read_only &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3289,6 +3329,38 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+					else		/* obtained the requested type, consume it */
+					{
+						/* We can release the address list now. */
+						release_conn_addrinfo(conn);
+
+						/* We are open for business! */
+						conn->status = CONNECTION_OK;
+						return PGRES_POLLING_OK;
+					}
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
 				/* We can release the address list now. */
@@ -3356,11 +3428,25 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						 conn->read_write_host_index != -2))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3373,16 +3459,27 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (!readonly_server && conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3391,7 +3488,7 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3575,6 +3672,7 @@ makeEmptyPGconn(void)
 	conn->sock = PGINVALID_SOCKET;
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 6961d7ce8e..4b0fc80df2 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -73,7 +73,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index b0ac98b90d..d6c482fd0b 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -363,7 +363,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -400,6 +403,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index beb45551a2..0e398136a5 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From b60953008e898e0127aa6912686a869d1b352b56 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 21 Feb 2019 23:11:55 +1100
Subject: [PATCH 1/6] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the transaction_readonly to find out whether
the server is read-write or not is restuctured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches
---
 doc/src/sgml/libpq.sgml           | 26 +++++---
 src/interfaces/libpq/fe-connect.c | 99 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  3 +-
 3 files changed, 57 insertions(+), 71 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c1d1b6b2db..ac78524924 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1576,17 +1576,27 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
      <varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
       <term><literal>target_session_attrs</literal></term>
       <listitem>
+       <para>
+        The supported options for this parameter are, <literal>any</literal> and
+        <literal>read-write</literal>. The default value of this parameter,
+        <literal>any</literal>, regards all connections as acceptable.
+        If multiple hosts were specified in the connection string, based on the
+        specified value, any remaining servers will be tried before confirming
+        succesful connection or failure.
+       </para>
+
        <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        To find out whether the server supports read-write transactions are not,
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection; if it returns <literal>on</literal>, means server
+        doesn't support read-write transactions.
+       </para>
       </listitem>
     </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index e3bf6a7449..c68448786d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3188,6 +3188,43 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_SETENV:
+			{
+
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
+				conn->status = CONNECTION_OK;
+
+				switch (pqSetenvPoll(conn))
+				{
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
+				}
+			}
+
+			/* Intentional fall through */
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3229,68 +3266,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
-			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
-				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
-				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
-				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
-			}
-
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 97bc98b1f3..50cfe266c6 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -65,8 +65,9 @@ typedef enum
 	CONNECTION_NEEDED,			/* Internal state: connect() needed */
 	CONNECTION_CHECK_WRITABLE,	/* Check if we could make a writable
 								 * connection. */
-	CONNECTION_CONSUME			/* Wait for any pending message and consume
+	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
+	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
 typedef enum
-- 
2.20.1.windows.1

From 8292bdeb1adf0a0270ed721d330877de0456180d Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH 2/6] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index c68448786d..1dc22e6bdf 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1243,8 +1243,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3233,8 +3236,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3540,6 +3542,8 @@ makeEmptyPGconn(void)
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 50cfe266c6..6961d7ce8e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -70,6 +70,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index dbe0f7e5c0..551120660c 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,6 +365,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.20.1.windows.1

From ec766623b19300c12121ce9ca694121fbb862354 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Sun, 17 Mar 2019 02:22:00 +1100
Subject: [PATCH 5/6] New read-only target_session_attrs type

With this read-only option type, application can connect to
connecting to a read-only server in the list of hosts, in case
if there is any read-only servers available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  2 +-
 src/interfaces/libpq/fe-connect.c     | 27 ++++++++++++++++++---------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 10 +++++++++-
 5 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7918e398c7..f7331fba32 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1578,7 +1578,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>, 
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 8de0d97876..2e16841703 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1249,6 +1249,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3249,7 +3251,7 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write or prefer-read connection is required, see
+				 * If a read-write, prefer-read or read-only connection is required, see
 				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
@@ -3287,8 +3289,9 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							  conn->read_write_host_index != -2))
+							  ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+								conn->read_write_host_index != -2) ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3322,6 +3325,7 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (!conn->transaction_read_only &&
+							conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
 							conn->read_write_host_index == -1)
 							conn->read_write_host_index = conn->whichhost;
 
@@ -3347,15 +3351,17 @@ keep_going:						/* We will come back to here until there is
 				 * Requested type is prefer-read, then record this host index
 				 * and try the other before considering it later
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					 conn->read_write_host_index != -2) ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3446,8 +3452,9 @@ keep_going:						/* We will come back to here until there is
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						 conn->read_write_host_index != -2))
+						 ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						   conn->read_write_host_index != -2) ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						PQclear(res);
@@ -3480,7 +3487,9 @@ keep_going:						/* We will come back to here until there is
 						sendTerminateConn(conn);
 
 						/* Record read-write host index */
-						if (!readonly_server && conn->read_write_host_index == -1)
+						if (!readonly_server &&
+							conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
 							conn->read_write_host_index = conn->whichhost;
 
 						/*
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 4b0fc80df2..5d0b885dae 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 13f971b5a5..62a1b7bbd4 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 0e398136a5..651107f49b 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 29;
+use Test::More tests => 31;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -129,6 +129,14 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From ed08223d1b9196f77dec63a8d746c21e602d2bb1 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 16:12:24 +1100
Subject: [PATCH 3/6] Make transaction_read_only as GUC_REPORT varaible

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index ac78524924..7b9d219bde 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1594,8 +1594,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, means server doesn't support read-write transactions.
+        But for servers version 12 or greater uses the <varname>transaction_read_only</varname>
+        GUC that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -1961,14 +1963,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index d66b860cbd..f3357b5c59 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index aa564d153a..d464be2c5b 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1503,7 +1503,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 1dc22e6bdf..0387d4fd09 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3238,26 +3238,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3538,6 +3573,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 6202653826..d2658efba5 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 551120660c..ccaee68be4 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -430,6 +430,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* session_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From 79fe61d2f9943aceca8ae5c88afe3c7312631b7d Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Sun, 17 Mar 2019 02:19:35 +1100
Subject: [PATCH 4/6] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 143 +++++++++++++++++++++-----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 161 insertions(+), 33 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7b9d219bde..7918e398c7 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1577,12 +1577,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>, 
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1591,6 +1591,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1600,7 +1607,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         GUC that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 0387d4fd09..8de0d97876 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1247,6 +1247,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2141,13 +2143,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is already
+				 * set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3229,7 +3249,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3257,13 +3278,19 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							  conn->read_write_host_index != -2))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
@@ -3276,16 +3303,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (!conn->transaction_read_only &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3293,6 +3332,38 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+					else		/* obtained the requested type, consume it */
+					{
+						/* We can release the address list now. */
+						release_conn_addrinfo(conn);
+
+						/* We are open for business! */
+						conn->status = CONNECTION_OK;
+						return PGRES_POLLING_OK;
+					}
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
 				/* We can release the address list now. */
@@ -3360,11 +3431,25 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						 conn->read_write_host_index != -2))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3377,16 +3462,27 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (!readonly_server && conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3395,7 +3491,7 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3579,6 +3675,7 @@ makeEmptyPGconn(void)
 	conn->sock = PGINVALID_SOCKET;
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 6961d7ce8e..4b0fc80df2 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -73,7 +73,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index ccaee68be4..13f971b5a5 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -363,7 +363,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -400,6 +403,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index beb45551a2..0e398136a5 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From 30af430274381220895382d2602537f7ae84ce40 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Sun, 17 Mar 2019 02:11:37 +1100
Subject: [PATCH 6/6] Primary, prefer-standby and standby options

New options to check whether the server is in recovery mode
or not, before considering them to connect. To confirm whether
the server is running in recovery mode or not, it sends the query
to server as 'SELECT pg_is_in_recovery()'.
---
 src/interfaces/libpq/fe-connect.c | 193 ++++++++++++++++++++++++++++--
 src/interfaces/libpq/libpq-fe.h   |   8 +-
 src/interfaces/libpq/libpq-int.h  |   2 +-
 3 files changed, 190 insertions(+), 13 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 2e16841703..16a1dd35b3 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -124,6 +124,7 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #define DefaultOption	""
 #define DefaultAuthtype		  ""
 #define DefaultTargetSessionAttrs	"any"
+#define DefaultTargetServerType	"any"
 #ifdef USE_SSL
 #define DefaultSSLMode "prefer"
 #else
@@ -322,7 +323,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1251,6 +1252,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2106,6 +2113,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_NEEDED:
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -3259,7 +3267,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+							conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3346,21 +3356,52 @@ keep_going:						/* We will come back to here until there is
 						return PGRES_POLLING_OK;
 					}
 				}
+				else if ((conn->sversion >= 90000 &&
+						(conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+							conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn,
+									 "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later
+				 * Requested type is prefer-read or prefer-standby, then record
+				 * this host index and try others before considering it later
 				 */
-				if ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+				if (((conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY) &&
 					 conn->read_write_host_index != -2) ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					(conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+							conn->requested_session_type == SESSION_TYPE_STANDBY))
 				{
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					if ((conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY) &&
 						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
@@ -3450,11 +3491,14 @@ keep_going:						/* We will come back to here until there is
 					 * is found in the first scan).
 					 */
 					if ((readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						 (conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+								 conn->requested_session_type == SESSION_TYPE_PRIMARY)) ||
 						(!readonly_server &&
-						 ((conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						 (((conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+								 conn->requested_session_type == SESSION_TYPE_PRIMARY) &&
 						   conn->read_write_host_index != -2) ||
-						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
+						  (conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+								  conn->requested_session_type == SESSION_TYPE_STANDBY))))
 					{
 						/* Not a requested type; fail this connection. */
 						PQclear(res);
@@ -3542,6 +3586,135 @@ keep_going:						/* We will come back to here until there is
 				goto keep_going;
 			}
 
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is primary,
+					 * ignore it. Server is not in recovery mode and requested mode is
+					 * prefer-standby, record it for the first time and try to
+					 * consume in the next scan (it means no standby server
+					 * is found in the first scan).
+					 */
+					if ((standby_server &&
+						  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (((conn->requested_session_type == SESSION_TYPE_PREFER_READ) &&
+						   conn->read_write_host_index != -2) ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is not in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record read-write host index */
+						if (!standby_server &&
+							conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 5d0b885dae..4c1b849019 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -67,7 +67,8 @@ typedef enum
 								 * connection. */
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -75,7 +76,10 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 62a1b7bbd4..f4e9c1f64b 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
-- 
2.20.1.windows.1

From 069f073d7d1e33c8a35689eef02666f52be391af Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 21 Feb 2019 23:11:55 +1100
Subject: [PATCH 1/7] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the transaction_readonly to find out whether
the server is read-write or not is restuctured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches
---
 doc/src/sgml/libpq.sgml           | 26 +++++---
 src/interfaces/libpq/fe-connect.c | 99 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  3 +-
 3 files changed, 57 insertions(+), 71 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c1d1b6b2db..ac78524924 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1576,17 +1576,27 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
      <varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
       <term><literal>target_session_attrs</literal></term>
       <listitem>
+       <para>
+        The supported options for this parameter are, <literal>any</literal> and
+        <literal>read-write</literal>. The default value of this parameter,
+        <literal>any</literal>, regards all connections as acceptable.
+        If multiple hosts were specified in the connection string, based on the
+        specified value, any remaining servers will be tried before confirming
+        succesful connection or failure.
+       </para>
+
        <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        To find out whether the server supports read-write transactions are not,
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection; if it returns <literal>on</literal>, means server
+        doesn't support read-write transactions.
+       </para>
       </listitem>
     </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index e3bf6a7449..c68448786d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3188,6 +3188,43 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_SETENV:
+			{
+
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
+				conn->status = CONNECTION_OK;
+
+				switch (pqSetenvPoll(conn))
+				{
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
+				}
+			}
+
+			/* Intentional fall through */
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3229,68 +3266,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
-			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
-				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
-				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
-				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
-			}
-
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 97bc98b1f3..50cfe266c6 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -65,8 +65,9 @@ typedef enum
 	CONNECTION_NEEDED,			/* Internal state: connect() needed */
 	CONNECTION_CHECK_WRITABLE,	/* Check if we could make a writable
 								 * connection. */
-	CONNECTION_CONSUME			/* Wait for any pending message and consume
+	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
+	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
 typedef enum
-- 
2.20.1.windows.1

From 695afa2f9404515a9dcb829782157fdcf7ca408d Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH 2/7] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index c68448786d..1dc22e6bdf 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1243,8 +1243,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3233,8 +3236,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3540,6 +3542,8 @@ makeEmptyPGconn(void)
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 50cfe266c6..6961d7ce8e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -70,6 +70,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index dbe0f7e5c0..551120660c 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,6 +365,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.20.1.windows.1

From c700c3a7bc4dd033b8a7a8ff2d00e108c80b11a0 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 16:12:24 +1100
Subject: [PATCH 3/7] Make transaction_read_only as GUC_REPORT varaible

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index ac78524924..7b9d219bde 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1594,8 +1594,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, means server doesn't support read-write transactions.
+        But for servers version 12 or greater uses the <varname>transaction_read_only</varname>
+        GUC that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -1961,14 +1963,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index d66b860cbd..f3357b5c59 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index aa564d153a..d464be2c5b 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1503,7 +1503,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 1dc22e6bdf..0387d4fd09 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3238,26 +3238,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3538,6 +3573,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 6202653826..d2658efba5 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 551120660c..ccaee68be4 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -430,6 +430,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* session_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From 2e5a27473b6c33a0ead839cede2c7e8823d3e047 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 17:35:07 +1100
Subject: [PATCH 5/7] New read-only target_session_attrs type

With this read-only option type, application can connect to
connecting to a read-only server in the list of hosts, in case
if there is any read-only servers available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  7 +++++-
 src/interfaces/libpq/fe-connect.c     | 34 ++++++++++++++++++++-------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 10 +++++++-
 5 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7918e398c7..79d122d756 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1578,7 +1578,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>, 
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1606,6 +1606,11 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         But for servers version 12 or greater uses the <varname>transaction_read_only</varname>
         GUC that is reported by the server upon successful connection.
        </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default.
+       </para>
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 4359a3e152..668bb9712d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1249,6 +1249,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3249,8 +3251,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write or prefer-read connection is required, see
-				 * if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3287,7 +3289,8 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3347,17 +3350,28 @@ keep_going:						/* We will come back to here until there is
 
 				/*
 				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
+					/*
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
+					 */
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
+
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3445,12 +3459,14 @@ keep_going:						/* We will come back to here until there is
 					 * ignore it. Server is read-write and requested mode is
 					 * prefer-read, record it for the first time and try to
 					 * consume in the next scan (it means no read-only server
-					 * is found in the first scan).
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
 					 */
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/*
 						 * The following scenario is possible only for the
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 4b0fc80df2..5d0b885dae 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 13f971b5a5..62a1b7bbd4 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 0e398136a5..651107f49b 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 29;
+use Test::More tests => 31;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -129,6 +129,14 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From eb62f768d0f89c6f7534b1432b86362f56f573ea Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Sun, 17 Mar 2019 02:19:35 +1100
Subject: [PATCH 4/7] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 161 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 177 insertions(+), 35 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7b9d219bde..7918e398c7 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1577,12 +1577,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>, 
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1591,6 +1591,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1600,7 +1607,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         GUC that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 0387d4fd09..4359a3e152 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1247,6 +1247,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2141,13 +2143,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3229,7 +3249,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3244,8 +3265,8 @@ keep_going:						/* We will come back to here until there is
 						 * Save existing error messages across the PQsendQuery
 						 * attempt.  This is necessary because PQsendQuery is
 						 * going to reset conn->errorMessage, so we would lose
-						 * error messages related to previous hosts we have tried
-						 * and failed to connect to.
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
 						 */
 						if (!saveErrorMessage(conn, &savedMessage))
 							goto error_return;
@@ -3257,16 +3278,30 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3276,16 +3311,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3293,8 +3340,36 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3360,11 +3435,33 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3377,16 +3474,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3395,7 +3504,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3579,6 +3689,7 @@ makeEmptyPGconn(void)
 	conn->sock = PGINVALID_SOCKET;
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 6961d7ce8e..4b0fc80df2 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -73,7 +73,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index ccaee68be4..13f971b5a5 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -363,7 +363,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -400,6 +403,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index beb45551a2..0e398136a5 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From cb6e88980096c2090d3d236837c331a6405a2aa3 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 17:47:09 +1100
Subject: [PATCH 6/7] Primary, prefer-standby and standby options

New options to check whether the server is in recovery mode
or not, before considering them to connect. To confirm whether
the server is running in recovery mode or not, it sends the query
to server as 'SELECT pg_is_in_recovery()'.
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 236 +++++++++++++++++++++++---
 src/interfaces/libpq/libpq-fe.h       |   8 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 262 insertions(+), 30 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 79d122d756..42dd93bd69 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1578,7 +1578,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>, 
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1611,6 +1612,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         If this parameter is set to <literal>read-only</literal>, only a connection
         in which read-only transactions are accepted by default.
        </para>
+       
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        where the server is not in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, only a connection in which
+        where the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        where the server is in recovery mode.
+       </para>
+
+       <para>
+        To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
+        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
+        is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 668bb9712d..7a75b692c8 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -124,6 +124,7 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #define DefaultOption	""
 #define DefaultAuthtype		  ""
 #define DefaultTargetSessionAttrs	"any"
+#define DefaultTargetServerType	"any"
 #ifdef USE_SSL
 #define DefaultSSLMode "prefer"
 #else
@@ -322,7 +323,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1251,6 +1252,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2106,6 +2113,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_NEEDED:
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2145,19 +2153,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means, failed to connect to read-only servers
 				 * and now try connect to read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3259,7 +3267,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3302,7 +3312,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
 						/* Append error report to conn->errorMessage. */
@@ -3333,8 +3343,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3349,30 +3359,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * severs before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
 				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
+				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3474,7 +3524,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
@@ -3509,8 +3559,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3563,6 +3613,144 @@ keep_going:						/* We will come back to here until there is
 				goto keep_going;
 			}
 
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is not in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3705,7 +3893,7 @@ makeEmptyPGconn(void)
 	conn->sock = PGINVALID_SOCKET;
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 5d0b885dae..4c1b849019 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -67,7 +67,8 @@ typedef enum
 								 * connection. */
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -75,7 +76,10 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 62a1b7bbd4..1591acdc8f 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -409,7 +409,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 651107f49b..f18fef4445 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 31;
+use Test::More tests => 35;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -137,6 +137,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From 185253d4379cc3985634f9344b06c7c8b6f0396b Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 18:11:18 +1100
Subject: [PATCH 7/7] New function to rejecting the checked write connection

When the connection is checked for write or not and based
on the result, if we decide to reject it, call the newly
added function to reject it.
---
 src/interfaces/libpq/fe-connect.c | 123 ++++++++++++------------------
 1 file changed, 47 insertions(+), 76 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7a75b692c8..82b80385d1 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2032,6 +2032,51 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+static void
+reject_checked_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3302,10 +3347,6 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
@@ -3315,42 +3356,7 @@ keep_going:						/* We will come back to here until there is
 						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3531,42 +3537,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
-- 
2.20.1.windows.1

From aa812716104b3fbd787dae4483341894c9e5ed9a Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 21 Feb 2019 23:11:55 +1100
Subject: [PATCH 1/8] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the SHOW transaction_readonly to find out whether
the server is read-write or not is restructured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches
---
 doc/src/sgml/libpq.sgml           | 26 +++++---
 src/interfaces/libpq/fe-connect.c | 99 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  3 +-
 3 files changed, 57 insertions(+), 71 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c1d1b6b2db..6221e359f0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1576,17 +1576,27 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
      <varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
       <term><literal>target_session_attrs</literal></term>
       <listitem>
+       <para>
+        The supported options for this parameter are, <literal>any</literal> and
+        <literal>read-write</literal>. The default value of this parameter,
+        <literal>any</literal>, regards all connections as acceptable.
+        If multiple hosts were specified in the connection string, based on the
+        specified value, any remaining servers will be tried before confirming
+        succesful connection or failure.
+       </para>
+
        <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        To find out whether the server supports read-write transactions are not,
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection; if it returns <literal>on</literal>, it means server
+        doesn't support read-write transactions.
+       </para>
       </listitem>
     </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index e3bf6a7449..c68448786d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3188,6 +3188,43 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_SETENV:
+			{
+
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
+				conn->status = CONNECTION_OK;
+
+				switch (pqSetenvPoll(conn))
+				{
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
+				}
+			}
+
+			/* Intentional fall through */
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3229,68 +3266,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
-			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
-				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
-				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
-				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
-			}
-
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 97bc98b1f3..50cfe266c6 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -65,8 +65,9 @@ typedef enum
 	CONNECTION_NEEDED,			/* Internal state: connect() needed */
 	CONNECTION_CHECK_WRITABLE,	/* Check if we could make a writable
 								 * connection. */
-	CONNECTION_CONSUME			/* Wait for any pending message and consume
+	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
+	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
 typedef enum
-- 
2.20.1.windows.1

From ebfa1b1e253aa661261760095d1a75293118161e Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH 2/8] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index c68448786d..1dc22e6bdf 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1243,8 +1243,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3233,8 +3236,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3540,6 +3542,8 @@ makeEmptyPGconn(void)
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 50cfe266c6..6961d7ce8e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -70,6 +70,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index dbe0f7e5c0..551120660c 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,6 +365,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.20.1.windows.1

From 45015c7271300e2a607d8a1211de361e8895f555 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:05:24 +1100
Subject: [PATCH 3/8] Make transaction_read_only as GUC_REPORT varaible

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 6221e359f0..fc5eec8450 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1594,8 +1594,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, it means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, it means server doesn't support read-write transactions.
+        But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
+        configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -1961,14 +1963,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index d66b860cbd..f3357b5c59 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index aa564d153a..d464be2c5b 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1503,7 +1503,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 1dc22e6bdf..0387d4fd09 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3238,26 +3238,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3538,6 +3573,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 6202653826..d2658efba5 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 551120660c..1154926391 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -430,6 +430,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From f7d15841528091b266da0ef43b47d1f4da21ed8d Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:56:48 +1100
Subject: [PATCH 4/8] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 161 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 177 insertions(+), 35 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index fc5eec8450..51b3e5a6f0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1577,12 +1577,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>,
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1591,6 +1591,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1600,7 +1607,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 0387d4fd09..4359a3e152 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1247,6 +1247,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2141,13 +2143,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3229,7 +3249,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3244,8 +3265,8 @@ keep_going:						/* We will come back to here until there is
 						 * Save existing error messages across the PQsendQuery
 						 * attempt.  This is necessary because PQsendQuery is
 						 * going to reset conn->errorMessage, so we would lose
-						 * error messages related to previous hosts we have tried
-						 * and failed to connect to.
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
 						 */
 						if (!saveErrorMessage(conn, &savedMessage))
 							goto error_return;
@@ -3257,16 +3278,30 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3276,16 +3311,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3293,8 +3340,36 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3360,11 +3435,33 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3377,16 +3474,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3395,7 +3504,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3579,6 +3689,7 @@ makeEmptyPGconn(void)
 	conn->sock = PGINVALID_SOCKET;
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 6961d7ce8e..4b0fc80df2 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -73,7 +73,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 1154926391..9fbce9888b 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -363,7 +363,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -400,6 +403,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index beb45551a2..0e398136a5 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From 536bf1d55e8c49ac02136503a8eab15c796f2226 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 18:02:59 +1100
Subject: [PATCH 5/8] New read-only target_session_attrs type

With this read-only option type, application can connect to
to a read-only server in the list of hosts, in case
if there is no read-only server available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  7 +++++-
 src/interfaces/libpq/fe-connect.c     | 34 ++++++++++++++++++++-------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 10 +++++++-
 5 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 51b3e5a6f0..a47081a265 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1578,7 +1578,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1606,6 +1606,11 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
         configuration parameter that is reported by the server upon successful connection.
        </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default.
+       </para>
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 4359a3e152..668bb9712d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1249,6 +1249,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3249,8 +3251,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write or prefer-read connection is required, see
-				 * if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3287,7 +3289,8 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3347,17 +3350,28 @@ keep_going:						/* We will come back to here until there is
 
 				/*
 				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
+					/*
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
+					 */
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
+
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3445,12 +3459,14 @@ keep_going:						/* We will come back to here until there is
 					 * ignore it. Server is read-write and requested mode is
 					 * prefer-read, record it for the first time and try to
 					 * consume in the next scan (it means no read-only server
-					 * is found in the first scan).
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
 					 */
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/*
 						 * The following scenario is possible only for the
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 4b0fc80df2..5d0b885dae 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 9fbce9888b..79ddd4d886 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 0e398136a5..651107f49b 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 29;
+use Test::More tests => 31;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -129,6 +129,14 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From 6802a581641d3082e6a15dbe06c838e64a6a8c2b Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 18:06:46 +1100
Subject: [PATCH 6/8] Primary, prefer-standby and standby options

New options to check whether the server is in recovery mode
or not, before considering them to connect. To confirm whether
the server is running in recovery mode or not, it sends the query
to server as 'SELECT pg_is_in_recovery()'.
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 236 +++++++++++++++++++++++---
 src/interfaces/libpq/libpq-fe.h       |   8 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 262 insertions(+), 30 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index a47081a265..328b632e16 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1578,7 +1578,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1611,6 +1612,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         If this parameter is set to <literal>read-only</literal>, only a connection
         in which read-only transactions are accepted by default.
        </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        where the server is not in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, only a connection in which
+        where the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        where the server is in recovery mode.
+       </para>
+
+       <para>
+        To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
+        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
+        is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 668bb9712d..7a75b692c8 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -124,6 +124,7 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #define DefaultOption	""
 #define DefaultAuthtype		  ""
 #define DefaultTargetSessionAttrs	"any"
+#define DefaultTargetServerType	"any"
 #ifdef USE_SSL
 #define DefaultSSLMode "prefer"
 #else
@@ -322,7 +323,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1251,6 +1252,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2106,6 +2113,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_NEEDED:
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2145,19 +2153,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means, failed to connect to read-only servers
 				 * and now try connect to read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3259,7 +3267,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3302,7 +3312,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
 						/* Append error report to conn->errorMessage. */
@@ -3333,8 +3343,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3349,30 +3359,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * severs before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
 				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
+				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3474,7 +3524,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
@@ -3509,8 +3559,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3563,6 +3613,144 @@ keep_going:						/* We will come back to here until there is
 				goto keep_going;
 			}
 
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is not in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3705,7 +3893,7 @@ makeEmptyPGconn(void)
 	conn->sock = PGINVALID_SOCKET;
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 5d0b885dae..4c1b849019 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -67,7 +67,8 @@ typedef enum
 								 * connection. */
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -75,7 +76,10 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 79ddd4d886..d60ee385a6 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -409,7 +409,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 651107f49b..f18fef4445 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 31;
+use Test::More tests => 35;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -137,6 +137,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From cbe3b9461a6fb4fcde4168f5a45ae0e6af0d900a Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 18:11:18 +1100
Subject: [PATCH 7/8] New function to rejecting the checked write connection

When the connection is checked for write or not and based
on the result, if we decide to reject it, call the newly
added function to reject it.
---
 src/interfaces/libpq/fe-connect.c | 123 ++++++++++++------------------
 1 file changed, 47 insertions(+), 76 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7a75b692c8..82b80385d1 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2032,6 +2032,51 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+static void
+reject_checked_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3302,10 +3347,6 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
@@ -3315,42 +3356,7 @@ keep_going:						/* We will come back to here until there is
 						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3531,42 +3537,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
-- 
2.20.1.windows.1

From b4c362af111487617f560df54fd0f2971628642d Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 28 Mar 2019 15:30:01 +1100
Subject: [PATCH 8/8] Server recovery mode handling

in_recovery GUC_REPORT is added to update the clients when the
server is recovery mode, this is useful for the client connections
to conenct to a standby server with a faster check instead of
executing a command.

New SIGUSR1 handling interrupt is added to support reporting
of recovery mode exit to all backends and their respective
clients.

Some parts of the code is taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.
---
 doc/src/sgml/libpq.sgml              |  14 ++-
 doc/src/sgml/protocol.sgml           |   8 +-
 src/backend/access/transam/xlog.c    |   9 ++
 src/backend/commands/async.c         |  53 +++++++++++
 src/backend/storage/ipc/procarray.c  |  30 ++++++
 src/backend/storage/ipc/procsignal.c |   3 +
 src/backend/storage/ipc/standby.c    |   9 ++
 src/backend/tcop/postgres.c          |   4 +
 src/backend/utils/misc/check_guc     |   2 +-
 src/backend/utils/misc/guc.c         |  17 +++-
 src/include/commands/async.h         |   5 +
 src/include/storage/procarray.h      |   1 +
 src/include/storage/procsignal.h     |   2 +
 src/include/storage/standby.h        |   1 +
 src/interfaces/libpq/fe-connect.c    | 133 +++++++++++++++++----------
 src/interfaces/libpq/fe-exec.c       |   4 +
 src/interfaces/libpq/libpq-int.h     |   1 +
 17 files changed, 237 insertions(+), 59 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 328b632e16..f3bbff9193 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1631,8 +1631,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
-        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
-        is in recovery mode.
+        will be sent upon any successful connection if the server is prior to version 12; if it returns
+        <literal>t</literal>, it means server is in recovery mode. But for server version 12 or greater
+        uses the value of <varname>in_recovery</varname> configuration parameter that is reported by the
+        server upon successful connection.
        </para>
 
       </listitem>
@@ -2000,15 +2002,17 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
        <varname>integer_datetimes</varname>,
-       <varname>standard_conforming_strings</varname>, and
-       <varname>transaction_read_only</varname>.
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before 9.0;
-       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index f3357b5c59..0da02263ea 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1284,15 +1284,17 @@ SELCT 1/0;
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
     <varname>integer_datetimes</varname>,
-    <varname>standard_conforming_strings</varname>, and
-    <varname>transaction_read_only</varname>.
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before 9.0;
-    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+    were not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 19d7911ec5..fa51c736fe 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7670,7 +7670,10 @@ StartupXLOG(void)
 	 * RecoverPreparedTransactions(), see notes for lock_twophase_recover()
 	 */
 	if (standbyState != STANDBY_DISABLED)
+	{
 		ShutdownRecoveryTransactionEnvironment();
+		SendRecoveryExitSignal();
+	}
 
 	/* Shut down xlogreader */
 	if (readFile >= 0)
@@ -7879,6 +7882,12 @@ RecoveryInProgress(void)
 			InitXLOGAccess();
 		}
 
+		/* Update in_recovery status. */
+		if (LocalRecoveryInProgress)
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 		/*
 		 * Note: We don't need a memory barrier when we're still in recovery.
 		 * We might exit recovery immediately after return, so the caller
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 5a7ee0de4c..934844523c 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -356,6 +356,15 @@ static List *upperPendingNotifies = NIL;	/* list of upper-xact lists */
  */
 volatile sig_atomic_t notifyInterruptPending = false;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* True if we've registered an on_shmem_exit cleanup */
 static bool unlistenExitRegistered = false;
 
@@ -1736,6 +1745,50 @@ ProcessNotifyInterrupt(void)
 		ProcessIncomingNotify();
 }
 
+/*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
 
 /*
  * Read all pending notifications from the queue, and deliver appropriate
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 010cc061c8..a5f3568d09 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2972,6 +2972,36 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 	return true;				/* timed out, still conflicts */
 }
 
+/*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+		{
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+		}
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
 /*
  * ProcArraySetReplicationSlotXmin
  *
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7605b2c367..e4548dc323 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,6 +292,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index cd56dca3ae..65f6ec7ca2 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -138,6 +138,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index f9ce3d8f22..d8d13f5a75 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -543,6 +543,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index d228bbed68..1c0f51ac8b 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_int \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index d464be2c5b..98795126d0 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -578,7 +578,7 @@ static char *recovery_target_xid_string;
 static char *recovery_target_time_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
-
+static bool in_recovery;
 
 /* should be static, but commands/variable.c needs to get at this */
 char	   *role_string;
@@ -1728,6 +1728,21 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"allow_system_table_mods", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
diff --git a/src/include/commands/async.h b/src/include/commands/async.h
index cfea78e039..7c0bbd3897 100644
--- a/src/include/commands/async.h
+++ b/src/include/commands/async.h
@@ -24,6 +24,7 @@
 
 extern bool Trace_notify;
 extern volatile sig_atomic_t notifyInterruptPending;
+extern volatile sig_atomic_t recoveryExitInterruptPending;
 
 extern Size AsyncShmemSize(void);
 extern void AsyncShmemInit(void);
@@ -54,4 +55,8 @@ extern void HandleNotifyInterrupt(void);
 /* process interrupts */
 extern void ProcessNotifyInterrupt(void);
 
+/* recovery exit interrupt handling functions */
+extern void HandleRecoveryExitInterrupt(void);
+extern void ProcessRecoveryExitInterrupt(void);
+
 #endif							/* ASYNC_H */
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index bd24850989..296d606e51 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 					 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
 						  int nxids, const TransactionId *xids,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 9f2f965d5c..722357c829 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 2361243514..3bb9023a6b 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 									RelFileNode node);
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 82b80385d1..15ac9866bd 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2077,6 +2077,49 @@ reject_checked_write_connection(PGconn *conn)
 	conn->try_next_host = true;
 }
 
+static void
+reject_checked_recovery_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3374,27 +3417,52 @@ keep_going:						/* We will come back to here until there is
 						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
 						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
 
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_RECOVERY;
+
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
 					}
+					else if ((conn->in_recovery &&
+							  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+							 (!conn->in_recovery &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_target_connection;
 
-					conn->status = CONNECTION_CHECK_RECOVERY;
+						reject_checked_recovery_connection(conn);
+						goto keep_going;
+					}
 
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
 				/*
@@ -3643,40 +3711,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is not in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record primary host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_recovery_connection(conn);
 						goto keep_going;
 					}
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index d2658efba5..38b8abcc44 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1117,6 +1117,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	{
 		conn->transaction_read_only = (strcmp(value, "on") == 0);
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index d60ee385a6..d135f3d9a3 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -442,6 +442,7 @@ struct pg_conn
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
 	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From 940a0da1da7378e7f9bf603a11d55eb984f5c427 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 21 Feb 2019 23:11:55 +1100
Subject: [PATCH 1/8] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the SHOW transaction_read_only to find out whether
the server is read-write or not is restructured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches
---
 doc/src/sgml/libpq.sgml           | 26 +++++---
 src/interfaces/libpq/fe-connect.c | 99 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  3 +-
 3 files changed, 57 insertions(+), 71 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index fe833aa626..67e81e98e1 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1647,17 +1647,27 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
      <varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
       <term><literal>target_session_attrs</literal></term>
       <listitem>
+       <para>
+        The supported options for this parameter are, <literal>any</literal> and
+        <literal>read-write</literal>. The default value of this parameter,
+        <literal>any</literal>, regards all connections as acceptable.
+        If multiple hosts were specified in the connection string, based on the
+        specified value, any remaining servers will be tried before confirming
+        succesful connection or failure.
+       </para>
+
        <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        To find out whether the server supports read-write transactions are not,
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection; if it returns <literal>on</literal>, it means server
+        doesn't support read-write transactions.
+       </para>
       </listitem>
     </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 87df79880a..9bb2e9631f 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3434,6 +3434,43 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_SETENV:
+			{
+
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
+				conn->status = CONNECTION_OK;
+
+				switch (pqSetenvPoll(conn))
+				{
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
+				}
+			}
+
+			/* Intentional fall through */
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3475,68 +3512,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
-			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
-				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
-				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
-				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
-			}
-
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index f44030b4b0..39579cd040 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -67,7 +67,8 @@ typedef enum
 								 * connection. */
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
-	CONNECTION_GSS_STARTUP		/* Negotiating GSSAPI. */
+	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
+	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
 typedef enum
-- 
2.20.1.windows.1

From 512be7c3a908437214926b43f8fc1a189a48cb54 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH 2/8] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 9bb2e9631f..24f203230b 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1294,8 +1294,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3479,8 +3482,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3789,6 +3791,8 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 39579cd040..ab415d684a 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -71,6 +71,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 1221ea9eef..6ba936dd10 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,6 +366,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.20.1.windows.1

From 5b05ff51abfd9368a434db4ba3ab5b6232b480ce Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:05:24 +1100
Subject: [PATCH 3/8] Make transaction_read_only as GUC_REPORT varaible

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 67e81e98e1..12bc0b3fce 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1665,8 +1665,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, it means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, it means server doesn't support read-write transactions.
+        But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
+        configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -2032,14 +2034,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 09893d96b5..d62ccceaa0 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index f7f726b5ae..045b659155 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1545,7 +1545,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 24f203230b..ca5e6d67d3 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3484,26 +3484,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3784,6 +3819,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 6202653826..d2658efba5 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 6ba936dd10..c50877e17a 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -431,6 +431,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From 7c8f2862fc28226c3b91aa2c676b6f7297027701 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:56:48 +1100
Subject: [PATCH 4/8] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 161 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 177 insertions(+), 35 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 12bc0b3fce..0d1e6a756c 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1648,12 +1648,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>,
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1662,6 +1662,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1671,7 +1678,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index ca5e6d67d3..a6a5df6fc5 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -340,7 +340,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1298,6 +1298,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2233,13 +2235,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3475,7 +3495,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3490,8 +3511,8 @@ keep_going:						/* We will come back to here until there is
 						 * Save existing error messages across the PQsendQuery
 						 * attempt.  This is necessary because PQsendQuery is
 						 * going to reset conn->errorMessage, so we would lose
-						 * error messages related to previous hosts we have tried
-						 * and failed to connect to.
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
 						 */
 						if (!saveErrorMessage(conn, &savedMessage))
 							goto error_return;
@@ -3503,16 +3524,30 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3522,16 +3557,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3539,8 +3586,36 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3606,11 +3681,33 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3623,16 +3720,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3641,7 +3750,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3828,6 +3938,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index ab415d684a..a57cfa1f93 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index c50877e17a..69c5d3e349 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -364,7 +364,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -401,6 +404,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index beb45551a2..0e398136a5 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 26;
+use Test::More tests => 29;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From 14c742dca19bb2e666ffd0a9e6bcb4a7a171e3cc Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 18:02:59 +1100
Subject: [PATCH 5/8] New read-only target_session_attrs type

With this read-only option type, application can connect
to a read-only server in the list of hosts, in case
if there is no read-only server available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  7 +++++-
 src/interfaces/libpq/fe-connect.c     | 34 ++++++++++++++++++++-------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 10 +++++++-
 5 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 0d1e6a756c..64ea89a960 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1677,6 +1677,11 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
         configuration parameter that is reported by the server upon successful connection.
        </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default.
+       </para>
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index a6a5df6fc5..4b2bf66fbc 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1300,6 +1300,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3495,8 +3497,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write or prefer-read connection is required, see
-				 * if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3533,7 +3535,8 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3593,17 +3596,28 @@ keep_going:						/* We will come back to here until there is
 
 				/*
 				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
+					/*
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
+					 */
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
+
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3691,12 +3705,14 @@ keep_going:						/* We will come back to here until there is
 					 * ignore it. Server is read-write and requested mode is
 					 * prefer-read, record it for the first time and try to
 					 * consume in the next scan (it means no read-only server
-					 * is found in the first scan).
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
 					 */
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/*
 						 * The following scenario is possible only for the
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index a57cfa1f93..76f4222f77 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -75,7 +75,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 69c5d3e349..dbba6935e8 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,7 +366,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 0e398136a5..651107f49b 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 29;
+use Test::More tests => 31;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -129,6 +129,14 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From f667b89d00f6540c6c44169f85ecee73f1a46876 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 10 Apr 2019 23:19:09 +1000
Subject: [PATCH 6/8] Primary, prefer-standby and standby options

New options to check whether the server is in recovery mode
or not, before considering them to connect. To confirm whether
the server is running in recovery mode or not, it sends the query
to server as 'SELECT pg_is_in_recovery()'.
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 236 +++++++++++++++++++++++---
 src/interfaces/libpq/libpq-fe.h       |   8 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 262 insertions(+), 30 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 64ea89a960..c8a1ae7afa 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1682,6 +1683,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         If this parameter is set to <literal>read-only</literal>, only a connection
         in which read-only transactions are accepted by default.
        </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        where the server is not in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, only a connection in which
+        where the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        where the server is in recovery mode.
+       </para>
+
+       <para>
+        To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
+        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
+        is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 4b2bf66fbc..027fefcf57 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -124,6 +124,7 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #define DefaultOption	""
 #define DefaultAuthtype		  ""
 #define DefaultTargetSessionAttrs	"any"
+#define DefaultTargetServerType	"any"
 #ifdef USE_SSL
 #define DefaultSSLMode "prefer"
 #else
@@ -340,7 +341,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1302,6 +1303,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2198,6 +2205,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2237,19 +2245,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means, failed to connect to read-only servers
 				 * and now try connect to read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3505,7 +3513,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3548,7 +3558,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
 						/* Append error report to conn->errorMessage. */
@@ -3579,8 +3589,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3595,30 +3605,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * severs before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
 				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
+				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3720,7 +3770,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
@@ -3755,8 +3805,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3809,6 +3859,144 @@ keep_going:						/* We will come back to here until there is
 				goto keep_going;
 			}
 
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is not in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3954,7 +4142,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 76f4222f77..bc1ab127ea 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	 CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -76,7 +77,10 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index dbba6935e8..e9583bfd95 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,7 +366,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -410,7 +410,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 651107f49b..f18fef4445 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 31;
+use Test::More tests => 35;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -137,6 +137,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 note "switching to physical replication slot";
 
 # Switch to using a physical replication slot. We can do this without a new
-- 
2.20.1.windows.1

From 0c24f713481021c2c249e83077c88d795e4a42be Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 18:11:18 +1100
Subject: [PATCH 7/8] New function to rejecting the checked write connection

When the connection is checked for write or not and based
on the result, if we decide to reject it, call the newly
added function to reject it.
---
 src/interfaces/libpq/fe-connect.c | 123 ++++++++++++------------------
 1 file changed, 47 insertions(+), 76 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 027fefcf57..6fd71b24f8 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2123,6 +2123,51 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+static void
+reject_checked_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3548,10 +3593,6 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
@@ -3561,42 +3602,7 @@ keep_going:						/* We will come back to here until there is
 						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3777,42 +3783,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
-- 
2.20.1.windows.1

From 58cd03e69d53270f6a2f252b68a59b284c996566 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 28 Mar 2019 15:30:01 +1100
Subject: [PATCH 8/8] Server recovery mode handling

in_recovery GUC_REPORT is added to update the clients when the
server is recovery mode, this is useful for the client connections
to connect to a standby server with a faster check instead of
executing a command.

New SIGUSR1 handling interrupt is added to support reporting
of recovery mode exit to all backends and their respective
clients.

Some parts of the code is taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.
---
 doc/src/sgml/libpq.sgml              |  14 ++-
 doc/src/sgml/protocol.sgml           |   8 +-
 src/backend/access/transam/xlog.c    |   3 +
 src/backend/commands/async.c         |   1 -
 src/backend/storage/ipc/procarray.c  |  28 ++++++
 src/backend/storage/ipc/procsignal.c |   3 +
 src/backend/storage/ipc/standby.c    |   9 ++
 src/backend/tcop/postgres.c          |  60 ++++++++++++
 src/backend/utils/init/postinit.c    |   6 +-
 src/backend/utils/misc/check_guc     |   2 +-
 src/backend/utils/misc/guc.c         |  17 +++-
 src/include/storage/procarray.h      |   1 +
 src/include/storage/procsignal.h     |   2 +
 src/include/storage/standby.h        |   1 +
 src/include/tcop/tcopprot.h          |   2 +
 src/interfaces/libpq/fe-connect.c    | 133 +++++++++++++++++----------
 src/interfaces/libpq/fe-exec.c       |   4 +
 src/interfaces/libpq/libpq-int.h     |   1 +
 18 files changed, 234 insertions(+), 61 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c8a1ae7afa..89a3f4c6e9 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1702,8 +1702,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
-        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
-        is in recovery mode.
+        will be sent upon any successful connection if the server is prior to version 12; if it returns
+        <literal>t</literal>, it means server is in recovery mode. But for server version 12 or greater
+        uses the value of <varname>in_recovery</varname> configuration parameter that is reported by the
+        server upon successful connection.
        </para>
 
       </listitem>
@@ -2071,15 +2073,17 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
        <varname>integer_datetimes</varname>,
-       <varname>standard_conforming_strings</varname>, and
-       <varname>transaction_read_only</varname>.
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before 9.0;
-       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index d62ccceaa0..a3984d6ac4 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1284,15 +1284,17 @@ SELCT 1/0;
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
     <varname>integer_datetimes</varname>,
-    <varname>standard_conforming_strings</varname>, and
-    <varname>transaction_read_only</varname>.
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before 9.0;
-    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+    were not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index c00b63c751..d2a0b4fd91 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7755,6 +7755,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryInProgress = false;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 5a7ee0de4c..9555da37d2 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -1736,7 +1736,6 @@ ProcessNotifyInterrupt(void)
 		ProcessIncomingNotify();
 }
 
-
 /*
  * Read all pending notifications from the queue, and deliver appropriate
  * ones to my frontend.  Stop when we reach queue head or an uncommitted
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 010cc061c8..75071d6b80 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2972,6 +2972,34 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 	return true;				/* timed out, still conflicts */
 }
 
+/*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
 /*
  * ProcArraySetReplicationSlotXmin
  *
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7605b2c367..e4548dc323 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,6 +292,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 215f1463bb..157a8442df 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -138,6 +138,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 44a59e1d4f..33511a9433 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -167,6 +167,15 @@ static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
 static StringInfoData row_description_buf;
@@ -195,6 +204,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -543,6 +553,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -2954,6 +2968,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 	errno = save_errno;
 }
 
+/*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
 /*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 1c2a99c9c8..1c4599af24 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -649,7 +649,11 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		 * This is handled by calling RecoveryInProgress and ignoring the
 		 * result.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index d228bbed68..1c0f51ac8b 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_int \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 045b659155..bcf4176c70 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -582,7 +582,7 @@ static char *recovery_target_xid_string;
 static char *recovery_target_time_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
-
+static bool in_recovery;
 
 /* should be static, but commands/variable.c needs to get at this */
 char	   *role_string;
@@ -1770,6 +1770,21 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"allow_system_table_mods", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index bd24850989..296d606e51 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 					 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
 						  int nxids, const TransactionId *xids,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 9f2f965d5c..722357c829 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 2361243514..3bb9023a6b 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 									RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index b367838612..d73ff7ff87 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -71,6 +71,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 6fd71b24f8..2989f3e5d0 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2168,6 +2168,49 @@ reject_checked_write_connection(PGconn *conn)
 	conn->try_next_host = true;
 }
 
+static void
+reject_checked_recovery_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3620,27 +3663,52 @@ keep_going:						/* We will come back to here until there is
 						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
 						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
 
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_RECOVERY;
+
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
 					}
+					else if ((conn->in_recovery &&
+							  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+							 (!conn->in_recovery &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_target_connection;
 
-					conn->status = CONNECTION_CHECK_RECOVERY;
+						reject_checked_recovery_connection(conn);
+						goto keep_going;
+					}
 
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
 				/*
@@ -3889,40 +3957,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is not in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record primary host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_recovery_connection(conn);
 						goto keep_going;
 					}
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index d2658efba5..38b8abcc44 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1117,6 +1117,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	{
 		conn->transaction_read_only = (strcmp(value, "on") == 0);
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index e9583bfd95..ee2f3da09c 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -443,6 +443,7 @@ struct pg_conn
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
 	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From 870435b9215901de59b651812f3af5af2bfad93a Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Tue, 12 Feb 2019 17:55:53 +1100
Subject: [PATCH] New pg_basebackup -g option to control the group access
 permissions

By default, pg_basebackup follows the backup file permissions
same as source instance, but with this option, user can control the
behavior.

--group-mode = inherit (default) (same permissions are source instance)
--group-mode = none (no group access permissions)
--group-mode = group (group access permissions)

The same applies to the database directory that is already present.

To support group access permissions for the tar mode, the
BASE BACKUP protocol is enhanced to support new option "GROUP_MODE"
with options "none" and "group". These options will be sent to the
server whenever user wants control the group access mode permissions
other than default.
---
 doc/src/sgml/protocol.sgml                   | 13 +++-
 doc/src/sgml/ref/pg_basebackup.sgml          | 48 ++++++++++++
 src/backend/replication/basebackup.c         | 46 +++++++++++
 src/backend/replication/repl_gram.y          |  8 +-
 src/backend/replication/repl_scanner.l       |  1 +
 src/bin/pg_basebackup/pg_basebackup.c        | 65 +++++++++++-----
 src/bin/pg_basebackup/streamutil.c           | 53 +++++++------
 src/bin/pg_basebackup/streamutil.h           | 11 +++
 src/bin/pg_basebackup/t/010_pg_basebackup.pl | 82 +++++++++++++++++++-
 9 files changed, 284 insertions(+), 43 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index b20f1690a7..c3611c53cf 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2466,7 +2466,7 @@ The commands accepted in replication mode are:
   </varlistentry>
 
   <varlistentry>
-    <term><literal>BASE_BACKUP</literal> [ <literal>LABEL</literal> <replaceable>'label'</replaceable> ] [ <literal>PROGRESS</literal> ] [ <literal>FAST</literal> ] [ <literal>WAL</literal> ] [ <literal>NOWAIT</literal> ] [ <literal>MAX_RATE</literal> <replaceable>rate</replaceable> ] [ <literal>TABLESPACE_MAP</literal> ] [ <literal>NOVERIFY_CHECKSUMS</literal> ]
+    <term><literal>BASE_BACKUP</literal> [ <literal>LABEL</literal> <replaceable>'label'</replaceable> ] [ <literal>PROGRESS</literal> ] [ <literal>FAST</literal> ] [ <literal>WAL</literal> ] [ <literal>NOWAIT</literal> ] [ <literal>MAX_RATE</literal> <replaceable>rate</replaceable> ] [ <literal>TABLESPACE_MAP</literal> ] [ <literal>NOVERIFY_CHECKSUMS</literal> ] [ <literal>GROUP_MODE</literal> <replaceable>'mode'</replaceable> ]
      <indexterm><primary>BASE_BACKUP</primary></indexterm>
     </term>
     <listitem>
@@ -2576,6 +2576,17 @@ The commands accepted in replication mode are:
          </para>
         </listitem>
        </varlistentry>
+       
+       <varlistentry>
+        <term><literal>GROUP_MODE</literal> <replaceable>'mode'</replaceable></term>
+        <listitem>
+         <para>
+          By default, the group access permissions will be same as source instance. If <literal>none</literal> is specified,
+          the backup files doesn't contains group access permissions. If <literal>group</literal> is specified, the backup
+          files should contains group access permissions.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist>
      </para>
      <para>
diff --git a/doc/src/sgml/ref/pg_basebackup.sgml b/doc/src/sgml/ref/pg_basebackup.sgml
index fc9e222f8d..89cf9895c8 100644
--- a/doc/src/sgml/ref/pg_basebackup.sgml
+++ b/doc/src/sgml/ref/pg_basebackup.sgml
@@ -536,6 +536,53 @@ PostgreSQL documentation
        </para>
       </listitem>
      </varlistentry>
+     
+     <varlistentry>
+      <term><option>-g <replaceable class="parameter">mode</replaceable></option></term>
+      <term><option>--group-mode=<replaceable class="parameter">mode</replaceable></option></term>
+      <listitem>
+       <para>
+        Controls the group permissions of the file in the backup. This option is ignored
+        on <productname>Windows</productname> as it does not support <acronym>POSIX</acronym>-style
+        group permissions. The following methods are available to control the group permissions:
+
+        <variablelist>
+         <varlistentry>
+          <term><literal>n</literal></term>
+          <term><literal>none</literal></term>
+          <listitem>
+           <para>
+            Don't include group access permissions in the backup.
+           </para>
+          </listitem>
+         </varlistentry>
+
+         <varlistentry>
+          <term><literal>i</literal></term>
+          <term><literal>inherit</literal></term>
+          <listitem>
+           <para>
+            Follow the same access permissions of the source instance.
+           </para>
+           <para>
+            This value is the default.
+           </para>
+          </listitem>
+         </varlistentry>
+
+         <varlistentry>
+          <term><literal>g</literal></term>
+          <term><literal>group</literal></term>
+          <listitem>
+           <para>
+            Include group access permissions for all the backup files.
+           </para>
+          </listitem>
+         </varlistentry>
+        </variablelist>
+       </para>
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
 
@@ -742,6 +789,7 @@ PostgreSQL documentation
    or an older major version, down to 9.1. However, WAL streaming mode (<literal>-X
    stream</literal>) only works with server version 9.3 and later, and tar format mode
    (<literal>--format=tar</literal>) of the current version only works with server version 9.5
+   or later. (<literal>-g</literal>) of the current version only works with server version 12
    or later.
   </para>
 
diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index c2978a949a..713c00d46d 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -54,6 +54,8 @@ typedef struct
 	bool		sendtblspcmapfile;
 } basebackup_options;
 
+static int	backup_dir_create_mode = 0;
+static int	backup_file_create_mode = 0;
 
 static int64 sendDir(const char *path, int basepathlen, bool sizeonly,
 					 List *tablespaces, bool sendtblspclinks);
@@ -650,6 +652,7 @@ parse_basebackup_options(List *options, basebackup_options *opt)
 	bool		o_maxrate = false;
 	bool		o_tablespace_map = false;
 	bool		o_noverify_checksums = false;
+	bool		o_group_mode = false;
 
 	MemSet(opt, 0, sizeof(*opt));
 	foreach(lopt, options)
@@ -738,6 +741,30 @@ parse_basebackup_options(List *options, basebackup_options *opt)
 			noverify_checksums = true;
 			o_noverify_checksums = true;
 		}
+		else if (strcmp(defel->defname, "group_mode") == 0)
+		{
+			if (o_group_mode)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("duplicate option \"%s\"", defel->defname)));
+
+			if (strcmp(strVal(defel->arg), "none") == 0)
+			{
+				backup_dir_create_mode = PG_DIR_MODE_OWNER;
+				backup_file_create_mode = PG_FILE_MODE_OWNER;
+			}
+			else if (strcmp(strVal(defel->arg), "group") == 0)
+			{
+				backup_dir_create_mode = PG_DIR_MODE_GROUP;
+				backup_file_create_mode = PG_FILE_MODE_GROUP;
+			}
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("Invalid option for group_mode \"%s\"", defel->defname)));
+
+			o_group_mode = true;
+		}
 		else
 			elog(ERROR, "option \"%s\" not recognized",
 				 defel->defname);
@@ -1602,6 +1629,25 @@ _tarWriteHeader(const char *filename, const char *linktarget,
 
 	if (!sizeonly)
 	{
+		/*
+		 * Adjust the mode of the file according to the backup request, ignore
+		 * it for tablespace links.
+		 */
+		if (!linktarget && backup_file_create_mode)
+		{
+			if (S_ISDIR(statbuf->st_mode))
+			{
+				statbuf->st_mode &= ~(pg_dir_create_mode);
+				statbuf->st_mode |= backup_dir_create_mode;
+			}
+			else
+			{
+				statbuf->st_mode &= ~(pg_file_create_mode);
+				statbuf->st_mode |= backup_file_create_mode;
+			}
+
+		}
+
 		rc = tarCreateHeader(h, filename, linktarget, statbuf->st_size,
 							 statbuf->st_mode, statbuf->st_uid, statbuf->st_gid,
 							 statbuf->st_mtime);
diff --git a/src/backend/replication/repl_gram.y b/src/backend/replication/repl_gram.y
index c4e11cc4e8..44059e299b 100644
--- a/src/backend/replication/repl_gram.y
+++ b/src/backend/replication/repl_gram.y
@@ -78,6 +78,7 @@ static SQLCmd *make_sqlcmd(void);
 %token K_WAL
 %token K_TABLESPACE_MAP
 %token K_NOVERIFY_CHECKSUMS
+%token K_GROUP_MODE
 %token K_TIMELINE
 %token K_PHYSICAL
 %token K_LOGICAL
@@ -155,7 +156,7 @@ var_name:	IDENT	{ $$ = $1; }
 
 /*
  * BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL] [NOWAIT]
- * [MAX_RATE %d] [TABLESPACE_MAP] [NOVERIFY_CHECKSUMS]
+ * [MAX_RATE %d] [TABLESPACE_MAP] [NOVERIFY_CHECKSUMS] [GROUP_MODE '<mode>']
  */
 base_backup:
 			K_BASE_BACKUP base_backup_opt_list
@@ -214,6 +215,11 @@ base_backup_opt:
 				  $$ = makeDefElem("noverify_checksums",
 								   (Node *)makeInteger(true), -1);
 				}
+			| K_GROUP_MODE SCONST
+				{
+				  $$ = makeDefElem("group_mode",
+								   (Node *)makeString($2), -1);
+				}
 			;
 
 create_replication_slot:
diff --git a/src/backend/replication/repl_scanner.l b/src/backend/replication/repl_scanner.l
index 380faeb5f6..7d1fde67bd 100644
--- a/src/backend/replication/repl_scanner.l
+++ b/src/backend/replication/repl_scanner.l
@@ -93,6 +93,7 @@ MAX_RATE		{ return K_MAX_RATE; }
 WAL			{ return K_WAL; }
 TABLESPACE_MAP			{ return K_TABLESPACE_MAP; }
 NOVERIFY_CHECKSUMS	{ return K_NOVERIFY_CHECKSUMS; }
+GROUP_MODE	{ return K_GROUP_MODE; }
 TIMELINE			{ return K_TIMELINE; }
 START_REPLICATION	{ return K_START_REPLICATION; }
 CREATE_REPLICATION_SLOT		{ return K_CREATE_REPLICATION_SLOT; }
diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index 9f0bede93b..a7d19d1072 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -350,6 +350,8 @@ usage(void)
 	printf(_("  -N, --no-sync          do not wait for changes to be written safely to disk\n"));
 	printf(_("  -P, --progress         show progress information\n"));
 	printf(_("  -S, --slot=SLOTNAME    replication slot to use\n"));
+	printf(_("  -g, --group-mode=inherit|group|none\n"
+			 "							specify required group access mode for basebackup directory\n"));
 	printf(_("  -v, --verbose          output verbose messages\n"));
 	printf(_("  -V, --version          output version information, then exit\n"));
 	printf(_("      --no-slot          prevent creation of temporary replication slot\n"));
@@ -676,6 +678,12 @@ verify_dir_is_empty_or_create(char *dirname, bool *created, bool *found)
 			/*
 			 * Exists, empty
 			 */
+			if (chmod(dirname, pg_dir_create_mode) != 0)
+			{
+				fprintf(stderr, _("%s: could not change permissions of directory \"%s\": %s\n"),
+						progname, dirname, strerror(errno));
+				exit(1);
+			}
 			if (found)
 				*found = true;
 			return;
@@ -1445,7 +1453,7 @@ ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum)
 
 		if (file == NULL)
 		{
-			int			filemode;
+			mode_t		oumask;
 
 			/*
 			 * No current file, so this must be the header for a new file
@@ -1459,9 +1467,6 @@ ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum)
 
 			current_len_left = read_tar_number(&copybuf[124], 12);
 
-			/* Set permissions on the file */
-			filemode = read_tar_number(&copybuf[100], 8);
-
 			/*
 			 * All files are padded up to 512 bytes
 			 */
@@ -1505,11 +1510,6 @@ ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum)
 							exit(1);
 						}
 					}
-#ifndef WIN32
-					if (chmod(filename, (mode_t) filemode))
-						pg_log_error("could not set permissions on directory \"%s\": %m",
-									 filename);
-#endif
 				}
 				else if (copybuf[156] == '2')
 				{
@@ -1547,19 +1547,15 @@ ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum)
 			/*
 			 * regular file
 			 */
+			oumask = umask(pg_mode_mask);
 			file = fopen(filename, "wb");
+			umask(oumask);
 			if (!file)
 			{
 				pg_log_error("could not create file \"%s\": %m", filename);
 				exit(1);
 			}
 
-#ifndef WIN32
-			if (chmod(filename, (mode_t) filemode))
-				pg_log_error("could not set permissions on file \"%s\": %m",
-							 filename);
-#endif
-
 			if (current_len_left == 0)
 			{
 				/*
@@ -1795,6 +1791,7 @@ BaseBackup(void)
 	char	   *basebkp;
 	char		escaped_label[MAXPGPATH];
 	char	   *maxrate_clause = NULL;
+	char	   *group_access_mode_clause = NULL;
 	int			i;
 	char		xlogstart[64];
 	char		xlogend[64];
@@ -1868,8 +1865,14 @@ BaseBackup(void)
 			fprintf(stderr, "\n");
 	}
 
+	/* Request server to send the file permissions according to the request */
+	if (group_access_mode == GROUP_ACCESS_NONE)
+		group_access_mode_clause = psprintf("GROUP_MODE '%s'", "none");
+	else if (group_access_mode == GROUP_ACCESS_PROVIDE)
+		group_access_mode_clause = psprintf("GROUP_MODE '%s'", "group");
+
 	basebkp =
-		psprintf("BASE_BACKUP LABEL '%s' %s %s %s %s %s %s %s",
+		psprintf("BASE_BACKUP LABEL '%s' %s %s %s %s %s %s %s %s",
 				 escaped_label,
 				 showprogress ? "PROGRESS" : "",
 				 includewal == FETCH_WAL ? "WAL" : "",
@@ -1877,7 +1880,8 @@ BaseBackup(void)
 				 includewal == NO_WAL ? "" : "NOWAIT",
 				 maxrate_clause ? maxrate_clause : "",
 				 format == 't' ? "TABLESPACE_MAP" : "",
-				 verify_checksums ? "" : "NOVERIFY_CHECKSUMS");
+				 verify_checksums ? "" : "NOVERIFY_CHECKSUMS",
+				 group_access_mode_clause ? group_access_mode_clause : "");
 
 	if (PQsendQuery(conn, basebkp) == 0)
 	{
@@ -2193,6 +2197,7 @@ main(int argc, char **argv)
 		{"status-interval", required_argument, NULL, 's'},
 		{"verbose", no_argument, NULL, 'v'},
 		{"progress", no_argument, NULL, 'P'},
+		{"group-mode", required_argument, NULL, 'g'},
 		{"waldir", required_argument, NULL, 1},
 		{"no-slot", no_argument, NULL, 2},
 		{"no-verify-checksums", no_argument, NULL, 3},
@@ -2223,7 +2228,7 @@ main(int argc, char **argv)
 
 	atexit(cleanup_directories_atexit);
 
-	while ((c = getopt_long(argc, argv, "CD:F:r:RS:T:X:l:nNzZ:d:c:h:p:U:s:wWkvP",
+	while ((c = getopt_long(argc, argv, "CD:F:r:RS:T:X:l:nNzZ:d:c:g:h:p:U:s:wWkvP",
 							long_options, &option_index)) != -1)
 	{
 		switch (c)
@@ -2361,6 +2366,30 @@ main(int argc, char **argv)
 			case 'P':
 				showprogress = true;
 				break;
+			case 'g':
+				if (strcmp(optarg, "i") == 0 ||
+					strcmp(optarg, "inherit") == 0)
+				{
+					group_access_mode = GROUP_ACCESS_INHERIT;
+				}
+				else if (strcmp(optarg, "g") == 0 ||
+						 strcmp(optarg, "group") == 0)
+				{
+					group_access_mode = GROUP_ACCESS_PROVIDE;
+				}
+				else if (strcmp(optarg, "n") == 0 ||
+						 strcmp(optarg, "none") == 0)
+				{
+					group_access_mode = GROUP_ACCESS_NONE;
+				}
+				else
+				{
+					fprintf(stderr,
+							_("%s: invalid group-mode option \"%s\", must be \"inherit\", \"group\", or \"none\"\n"),
+							progname, optarg);
+					exit(1);
+				}
+				break;
 			case 3:
 				verify_checksums = false;
 				break;
diff --git a/src/bin/pg_basebackup/streamutil.c b/src/bin/pg_basebackup/streamutil.c
index 79f17e4089..66bd8cd877 100644
--- a/src/bin/pg_basebackup/streamutil.c
+++ b/src/bin/pg_basebackup/streamutil.c
@@ -33,6 +33,7 @@
 #define ERRCODE_DUPLICATE_OBJECT  "42710"
 
 uint32		WalSegSz;
+GroupAccessMode group_access_mode = GROUP_ACCESS_INHERIT;
 
 static bool RetrieveDataDirCreatePerm(PGconn *conn);
 
@@ -364,36 +365,44 @@ RetrieveDataDirCreatePerm(PGconn *conn)
 	if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_GROUP_ACCESS)
 		return true;
 
-	res = PQexec(conn, "SHOW data_directory_mode");
-	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	if (group_access_mode == GROUP_ACCESS_INHERIT)
 	{
-		pg_log_error("could not send replication command \"%s\": %s",
-					 "SHOW data_directory_mode", PQerrorMessage(conn));
+		res = PQexec(conn, "SHOW data_directory_mode");
+		if (PQresultStatus(res) != PGRES_TUPLES_OK)
+		{
+			pg_log_error("could not send replication command \"%s\": %s",
+						 "SHOW data_directory_mode", PQerrorMessage(conn));
 
-		PQclear(res);
-		return false;
-	}
-	if (PQntuples(res) != 1 || PQnfields(res) < 1)
-	{
-		pg_log_error("could not fetch group access flag: got %d rows and %d fields, expected %d rows and %d or more fields",
-					 PQntuples(res), PQnfields(res), 1, 1);
+			PQclear(res);
+			return false;
+		}
+		if (PQntuples(res) != 1 || PQnfields(res) < 1)
+		{
+			pg_log_error("could not fetch group access flag: got %d rows and %d fields, expected %d rows and %d or more fields",
+						 PQntuples(res), PQnfields(res), 1, 1);
 
-		PQclear(res);
-		return false;
-	}
+			PQclear(res);
+			return false;
+		}
 
-	if (sscanf(PQgetvalue(res, 0, 0), "%o", &data_directory_mode) != 1)
-	{
-		pg_log_error("group access flag could not be parsed: %s",
-					 PQgetvalue(res, 0, 0));
+		if (sscanf(PQgetvalue(res, 0, 0), "%o", &data_directory_mode) != 1)
+		{
+			pg_log_error("group access flag could not be parsed: %s",
+						 PQgetvalue(res, 0, 0));
+
+			PQclear(res);
+			return false;
+		}
+
+		SetDataDirectoryCreatePerm(data_directory_mode);
 
 		PQclear(res);
-		return false;
 	}
+	else if (group_access_mode == GROUP_ACCESS_NONE)
+		SetDataDirectoryCreatePerm(PG_DIR_MODE_OWNER);
+	else
+		SetDataDirectoryCreatePerm(PG_DIR_MODE_GROUP);
 
-	SetDataDirectoryCreatePerm(data_directory_mode);
-
-	PQclear(res);
 	return true;
 }
 
diff --git a/src/bin/pg_basebackup/streamutil.h b/src/bin/pg_basebackup/streamutil.h
index a756eee262..7438cc5062 100644
--- a/src/bin/pg_basebackup/streamutil.h
+++ b/src/bin/pg_basebackup/streamutil.h
@@ -17,6 +17,16 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 
+/*
+ * Different ways to specify group access mode
+ */
+typedef enum
+{
+	GROUP_ACCESS_INHERIT = 0,
+	GROUP_ACCESS_PROVIDE,
+	GROUP_ACCESS_NONE
+}			GroupAccessMode;
+
 extern const char *progname;
 extern char *connection_string;
 extern char *dbhost;
@@ -25,6 +35,7 @@ extern char *dbport;
 extern char *dbname;
 extern int	dbgetpassword;
 extern uint32 WalSegSz;
+extern GroupAccessMode group_access_mode;
 
 /* Connection kept global so we can disconnect easily */
 extern PGconn *conn;
diff --git a/src/bin/pg_basebackup/t/010_pg_basebackup.pl b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
index b7d36b65dd..f5dc451f86 100644
--- a/src/bin/pg_basebackup/t/010_pg_basebackup.pl
+++ b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
@@ -6,7 +6,7 @@ use File::Basename qw(basename dirname);
 use File::Path qw(rmtree);
 use PostgresNode;
 use TestLib;
-use Test::More tests => 106;
+use Test::More tests => 118;
 
 program_help_ok('pg_basebackup');
 program_version_ok('pg_basebackup');
@@ -402,6 +402,86 @@ $node->command_ok(
 	'pg_basebackup -X stream runs with --no-slot');
 rmtree("$tempdir/backupnoslot");
 
+# The following tests test backup unix file permissions. Windows doesn't support
+# unix file permissions, so skip on Windows.
+SKIP:
+{
+	skip "unix style file permissions are not supported on Windows", 18 if ($windows_os);
+
+	$node->stop;
+
+	# Set umask so test directories and files are created with default permissions
+	umask(0077);
+
+	# Enable no group permissions on PGDATA
+	chmod_recursive("$pgdata", 0700, 0600);
+
+	$node->start;
+	
+	$node->command_ok([ 'pg_basebackup', '-D', "$tempdir/backupP", '-g', 'group' ],
+		'pg_basebackup -g group runs');
+
+	# Group access should be enabled on all backup files
+	ok(check_mode_recursive("$tempdir/backupP", 0750, 0640),
+		"check backup dir permissions");
+	rmtree("$tempdir/backupP");
+	
+	$node->command_ok([ 'pg_basebackup', '-D', "$tempdir/backupP", '-g', 'inherit' ],
+		'pg_basebackup -g inherit runs');
+
+	# Group access should be not enabled on all backup files
+	ok(check_mode_recursive("$tempdir/backupP", 0700, 0600),
+		"check backup dir permissions");
+	rmtree("$tempdir/backupP");
+
+	$node->command_ok([ 'pg_basebackup', '-D', "$tempdir/backupP", '-g', 'group', '-Ft' ],
+		'pg_basebackup -g group in tar mode runs');
+
+	system_or_bail 'tar', '-xvf', "$tempdir/backupP/base.tar";
+
+	# Group access should be enabled on all backup files
+	ok(check_mode_recursive("$tempdir/backupP", 0750, 0640),
+		"check backup dir permissions");
+	rmtree("$tempdir/backupP");
+
+	
+	$node->stop;
+
+	# Set umask so test directories and files are created with group permissions
+	umask(0027);
+
+	# Enable no group permissions on PGDATA
+	chmod_recursive("$pgdata", 0750, 0640);
+
+	$node->start;
+	
+	$node->command_ok([ 'pg_basebackup', '-D', "$tempdir/backupP", ],
+		'pg_basebackup default runs');
+
+	# Group access should be enabled on all backup files
+	ok(check_mode_recursive("$tempdir/backupP", 0750, 0640),
+		"check backup dir permissions");
+	rmtree("$tempdir/backupP");
+	
+	$node->command_ok([ 'pg_basebackup', '-D', "$tempdir/backupP", '-g', 'none'],
+	'pg_basebackup -g none runs');
+
+	# Group access should be not enabled on all backup files
+	ok(check_mode_recursive("$tempdir/backupP", 0700, 0600),
+		"check backup dir permissions");
+	rmtree("$tempdir/backupP");
+
+	$node->command_ok([ 'pg_basebackup', '-D', "$tempdir/backupP", '-g', 'none', '-Ft' ],
+		'pg_basebackup -g none in tar mode runs');
+
+	system_or_bail 'tar', '-xvf', "$tempdir/backupP/base.tar";
+
+	# Group access should be not enabled on all backup files
+	ok(check_mode_recursive("$tempdir/backupP", 0700, 0600),
+		"check backup dir permissions");
+	rmtree("$tempdir/backupP");
+}
+
 $node->command_fails(
 	[
 		'pg_basebackup',             '-D',
-- 
2.20.1.windows.1

From 22d8f6c851cd7e55838ad4bcf6937b55b7144b8a Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH 2/8] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 44055a5682..ce690b052c 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1294,8 +1294,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3480,8 +3483,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3790,6 +3792,8 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index ef21864abf..b76022a96e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -71,6 +71,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index c0b8e3f8ce..4f0d20a696 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,6 +366,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.20.1.windows.1

From b9b1f02096412c8d2c3c4c23d71f4d98b46e0737 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:05:24 +1100
Subject: [PATCH 3/8] Make transaction_read_only as GUC_REPORT variable

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 17310eb077..6107755416 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1665,8 +1665,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, it means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, it means server doesn't support read-write transactions.
+        But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
+        configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -2032,14 +2034,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index b20f1690a7..05286c7365 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELECT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 1208eb9a68..e86b4d3319 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1545,7 +1545,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index ce690b052c..8bdabdf3b5 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3485,26 +3485,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3785,6 +3820,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 3a8cddf4ff..701c4a66fe 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 4f0d20a696..caddf0ddc5 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -431,6 +431,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From afe1430861a0d7a6d76c4511c14aaa9e47a2f095 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:56:48 +1100
Subject: [PATCH 4/8] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 161 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 177 insertions(+), 35 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 6107755416..67f2c6a5c1 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1648,12 +1648,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>,
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1662,6 +1662,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1671,7 +1678,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 8bdabdf3b5..df2c190a3f 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -340,7 +340,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1298,6 +1298,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2233,13 +2235,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3476,7 +3496,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3491,8 +3512,8 @@ keep_going:						/* We will come back to here until there is
 						 * Save existing error messages across the PQsendQuery
 						 * attempt.  This is necessary because PQsendQuery is
 						 * going to reset conn->errorMessage, so we would lose
-						 * error messages related to previous hosts we have tried
-						 * and failed to connect to.
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
 						 */
 						if (!saveErrorMessage(conn, &savedMessage))
 							goto error_return;
@@ -3504,16 +3525,30 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3523,16 +3558,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3540,8 +3587,36 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3607,11 +3682,33 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3624,16 +3721,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3642,7 +3751,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3829,6 +3939,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index b76022a96e..f3833678e2 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index caddf0ddc5..4e8bab3822 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -364,7 +364,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -401,6 +404,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 3c743d7d7c..af465be505 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 32;
+use Test::More tests => 35;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -121,6 +121,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.20.1.windows.1

From 0410c3a0740d5ed68ea9d107393546d3d67d9541 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 18:02:59 +1100
Subject: [PATCH 5/8] New read-only target_session_attrs type

With this read-only option type, application can connect
to a read-only server in the list of hosts, in case
if there is no read-only server available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  7 +++++-
 src/interfaces/libpq/fe-connect.c     | 34 ++++++++++++++++++++-------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 10 +++++++-
 5 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 67f2c6a5c1..2be51b2a49 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1677,6 +1677,11 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
         configuration parameter that is reported by the server upon successful connection.
        </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default.
+       </para>
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index df2c190a3f..38cbb07828 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1300,6 +1300,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3496,8 +3498,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write or prefer-read connection is required, see
-				 * if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3534,7 +3536,8 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3594,17 +3597,28 @@ keep_going:						/* We will come back to here until there is
 
 				/*
 				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
+					/*
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
+					 */
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
+
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3692,12 +3706,14 @@ keep_going:						/* We will come back to here until there is
 					 * ignore it. Server is read-write and requested mode is
 					 * prefer-read, record it for the first time and try to
 					 * consume in the next scan (it means no read-only server
-					 * is found in the first scan).
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
 					 */
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/*
 						 * The following scenario is possible only for the
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index f3833678e2..a015579c43 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -75,7 +75,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 4e8bab3822..a00d8bddeb 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,7 +366,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index af465be505..ac1e11e1ab 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 35;
+use Test::More tests => 37;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -133,6 +133,14 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.20.1.windows.1

From b816e48049cb41c9390761e5cb2546447ada38a2 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 10 Apr 2019 23:19:09 +1000
Subject: [PATCH 6/8] Primary, prefer-standby and standby options

New options to check whether the server is in recovery mode
or not, before considering them to connect. To confirm whether
the server is running in recovery mode or not, it sends the query
to server as 'SELECT pg_is_in_recovery()'.
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 236 +++++++++++++++++++++++---
 src/interfaces/libpq/libpq-fe.h       |   8 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 262 insertions(+), 30 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 2be51b2a49..6b84accd08 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1682,6 +1683,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         If this parameter is set to <literal>read-only</literal>, only a connection
         in which read-only transactions are accepted by default.
        </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        where the server is not in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, only a connection in which
+        where the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        where the server is in recovery mode.
+       </para>
+
+       <para>
+        To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
+        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
+        is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 38cbb07828..a6e0959895 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -124,6 +124,7 @@ static int	ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #define DefaultOption	""
 #define DefaultAuthtype		  ""
 #define DefaultTargetSessionAttrs	"any"
+#define DefaultTargetServerType	"any"
 #ifdef USE_SSL
 #define DefaultSSLMode "prefer"
 #else
@@ -340,7 +341,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1302,6 +1303,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2198,6 +2205,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2237,19 +2245,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means, failed to connect to read-only servers
 				 * and now try connect to read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3506,7 +3514,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3549,7 +3559,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
 						/* Append error report to conn->errorMessage. */
@@ -3580,8 +3590,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3596,30 +3606,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * severs before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
 				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
+				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3721,7 +3771,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
@@ -3756,8 +3806,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3810,6 +3860,144 @@ keep_going:						/* We will come back to here until there is
 				goto keep_going;
 			}
 
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is not in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3955,7 +4143,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index a015579c43..6c5780c672 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	 CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -76,7 +77,10 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index a00d8bddeb..740033e116 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,7 +366,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -410,7 +410,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index ac1e11e1ab..8fa28dab23 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 37;
+use Test::More tests => 41;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -141,6 +141,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.20.1.windows.1

From 65e9a74dfe5f8fb4bf84cd7df8da93d32662a282 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 18:11:18 +1100
Subject: [PATCH 7/8] New function to rejecting the checked write connection

When the connection is checked for write or not and based
on the result, if we decide to reject it, call the newly
added function to reject it.
---
 src/interfaces/libpq/fe-connect.c | 123 ++++++++++++------------------
 1 file changed, 47 insertions(+), 76 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index a6e0959895..94a537927a 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2123,6 +2123,51 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+static void
+reject_checked_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3549,10 +3594,6 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
@@ -3562,42 +3603,7 @@ keep_going:						/* We will come back to here until there is
 						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3778,42 +3784,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
-- 
2.20.1.windows.1

From 05da6b0dcf5a9255ee62a0bac667f3a13366502d Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 28 Mar 2019 15:30:01 +1100
Subject: [PATCH 8/8] Server recovery mode handling

in_recovery GUC_REPORT is added to update the clients when the
server is recovery mode, this is useful for the client connections
to connect to a standby server with a faster check instead of
executing a command.

New SIGUSR1 handling interrupt is added to support reporting
of recovery mode exit to all backends and their respective
clients.

Some parts of the code is taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.
---
 doc/src/sgml/libpq.sgml              |  14 ++-
 doc/src/sgml/protocol.sgml           |   8 +-
 src/backend/access/transam/xlog.c    |   3 +
 src/backend/commands/async.c         |   1 -
 src/backend/storage/ipc/procarray.c  |  28 ++++++
 src/backend/storage/ipc/procsignal.c |   3 +
 src/backend/storage/ipc/standby.c    |   9 ++
 src/backend/tcop/postgres.c          |  60 ++++++++++++
 src/backend/utils/init/postinit.c    |   6 +-
 src/backend/utils/misc/check_guc     |   2 +-
 src/backend/utils/misc/guc.c         |  17 +++-
 src/include/storage/procarray.h      |   1 +
 src/include/storage/procsignal.h     |   2 +
 src/include/storage/standby.h        |   1 +
 src/include/tcop/tcopprot.h          |   2 +
 src/interfaces/libpq/fe-connect.c    | 133 +++++++++++++++++----------
 src/interfaces/libpq/fe-exec.c       |   4 +
 src/interfaces/libpq/libpq-int.h     |   1 +
 18 files changed, 234 insertions(+), 61 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 6b84accd08..90e8c96820 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1702,8 +1702,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
-        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
-        is in recovery mode.
+        will be sent upon any successful connection if the server is prior to version 12; if it returns
+        <literal>t</literal>, it means server is in recovery mode. But for server version 12 or greater
+        uses the value of <varname>in_recovery</varname> configuration parameter that is reported by the
+        server upon successful connection.
        </para>
 
       </listitem>
@@ -2071,15 +2073,17 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
        <varname>integer_datetimes</varname>,
-       <varname>standard_conforming_strings</varname>, and
-       <varname>transaction_read_only</varname>.
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before 9.0;
-       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 05286c7365..9ed2a03b73 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1284,15 +1284,17 @@ SELECT 1/0;
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
     <varname>integer_datetimes</varname>,
-    <varname>standard_conforming_strings</varname>, and
-    <varname>transaction_read_only</varname>.
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before 9.0;
-    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+    were not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 1c7dd51b9f..976e6f63ae 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7755,6 +7755,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryInProgress = false;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 738e6ec7e2..102094e765 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -1736,7 +1736,6 @@ ProcessNotifyInterrupt(void)
 		ProcessIncomingNotify();
 }
 
-
 /*
  * Read all pending notifications from the queue, and deliver appropriate
  * ones to my frontend.  Stop when we reach queue head or an uncommitted
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 18a0f62ba6..ad72ab10c7 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2972,6 +2972,34 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 	return true;				/* timed out, still conflicts */
 }
 
+/*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
 /*
  * ProcArraySetReplicationSlotXmin
  *
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7605b2c367..e4548dc323 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,6 +292,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 842fcabd97..831cd80357 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -138,6 +138,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 44a59e1d4f..33511a9433 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -167,6 +167,15 @@ static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
 static StringInfoData row_description_buf;
@@ -195,6 +204,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -543,6 +553,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -2954,6 +2968,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 	errno = save_errno;
 }
 
+/*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
 /*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index e9f72b5069..29a159dc11 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -651,7 +651,11 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		 * This is handled by calling RecoveryInProgress and ignoring the
 		 * result.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index d228bbed68..1c0f51ac8b 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_int \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index e86b4d3319..23b5b3e46c 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -582,7 +582,7 @@ static char *recovery_target_xid_string;
 static char *recovery_target_time_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
-
+static bool in_recovery;
 
 /* should be static, but commands/variable.c needs to get at this */
 char	   *role_string;
@@ -1771,6 +1771,21 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"allow_system_table_mods", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index da8b672096..86f0c13134 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
 									  int nxids, const TransactionId *xids,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 05b186a05c..9cf9560b06 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index a3f8f82ff3..2c73f0c0a8 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index 8dcfb40728..7b7bfe0209 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -71,6 +71,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 94a537927a..6f13d099e2 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2168,6 +2168,49 @@ reject_checked_write_connection(PGconn *conn)
 	conn->try_next_host = true;
 }
 
+static void
+reject_checked_recovery_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3621,27 +3664,52 @@ keep_going:						/* We will come back to here until there is
 						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
 						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
 
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_RECOVERY;
+
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
 					}
+					else if ((conn->in_recovery &&
+							  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+							 (!conn->in_recovery &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_target_connection;
 
-					conn->status = CONNECTION_CHECK_RECOVERY;
+						reject_checked_recovery_connection(conn);
+						goto keep_going;
+					}
 
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
 				/*
@@ -3890,40 +3958,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is not in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record primary host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_recovery_connection(conn);
 						goto keep_going;
 					}
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 701c4a66fe..7cffed57cd 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1117,6 +1117,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	{
 		conn->transaction_read_only = (strcmp(value, "on") == 0);
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 740033e116..7b36ddb804 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -443,6 +443,7 @@ struct pg_conn
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
 	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.20.1.windows.1

From 724e98a9633c949665867eef43e701d6e5bdadf8 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 21 Feb 2019 23:11:55 +1100
Subject: [PATCH 1/8] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the SHOW transaction_read_only to find out whether
the server is read-write or not is restructured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches
---
 doc/src/sgml/libpq.sgml           | 26 +++++---
 src/interfaces/libpq/fe-connect.c | 99 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  3 +-
 3 files changed, 57 insertions(+), 71 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7f01fcc148..17310eb077 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1647,17 +1647,27 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
      <varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
       <term><literal>target_session_attrs</literal></term>
       <listitem>
+       <para>
+        The supported options for this parameter are, <literal>any</literal> and
+        <literal>read-write</literal>. The default value of this parameter,
+        <literal>any</literal>, regards all connections as acceptable.
+        If multiple hosts were specified in the connection string, based on the
+        specified value, any remaining servers will be tried before confirming
+        succesful connection or failure.
+       </para>
+
        <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        To find out whether the server supports read-write transactions are not,
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection; if it returns <literal>on</literal>, it means server
+        doesn't support read-write transactions.
+       </para>
       </listitem>
     </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index c800d7921e..6e70f4abd7 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3433,6 +3433,43 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_SETENV:
+			{
+
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
+				conn->status = CONNECTION_OK;
+
+				switch (pqSetenvPoll(conn))
+				{
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
+				}
+			}
+
+			/* Intentional fall through */
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3474,68 +3511,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
-			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
-				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
-				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
-				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
-			}
-
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 26198fc1de..ef21864abf 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -67,7 +67,8 @@ typedef enum
 								 * connection. */
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
-	CONNECTION_GSS_STARTUP		/* Negotiating GSSAPI. */
+	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
+	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
 typedef enum
-- 
2.21.0

From 39bc86ec043aa043d070c0d4a8be86176fd50584 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH 2/8] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 6e70f4abd7..8b2d46d31c 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1294,8 +1294,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3478,8 +3481,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3788,6 +3790,8 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index ef21864abf..b76022a96e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -71,6 +71,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index c0b8e3f8ce..4f0d20a696 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,6 +366,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.21.0

From 1eaf6bd08575935e223569e1c4fb8dcf19439246 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:05:24 +1100
Subject: [PATCH 3/8] Make transaction_read_only as GUC_REPORT variable

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 17310eb077..6107755416 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1665,8 +1665,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, it means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, it means server doesn't support read-write transactions.
+        But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
+        configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -2032,14 +2034,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index b20f1690a7..05286c7365 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELECT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 92c4fee8f8..5357e51d3f 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1544,7 +1544,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 8b2d46d31c..eceb586fb2 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3483,26 +3483,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3783,6 +3818,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 3a8cddf4ff..701c4a66fe 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 4f0d20a696..caddf0ddc5 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -431,6 +431,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.21.0

From 0379a556ac79f76cbe690b5fad5bbae293d4b53c Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:56:48 +1100
Subject: [PATCH 4/8] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 161 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 177 insertions(+), 35 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 6107755416..67f2c6a5c1 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1648,12 +1648,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>,
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1662,6 +1662,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1671,7 +1678,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index eceb586fb2..59ee803340 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -340,7 +340,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1298,6 +1298,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2231,13 +2233,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3474,7 +3494,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3489,8 +3510,8 @@ keep_going:						/* We will come back to here until there is
 						 * Save existing error messages across the PQsendQuery
 						 * attempt.  This is necessary because PQsendQuery is
 						 * going to reset conn->errorMessage, so we would lose
-						 * error messages related to previous hosts we have tried
-						 * and failed to connect to.
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
 						 */
 						if (!saveErrorMessage(conn, &savedMessage))
 							goto error_return;
@@ -3502,16 +3523,30 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3521,16 +3556,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3538,8 +3585,36 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3605,11 +3680,33 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3622,16 +3719,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3640,7 +3749,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3827,6 +3937,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index b76022a96e..f3833678e2 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index caddf0ddc5..4e8bab3822 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -364,7 +364,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -401,6 +404,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 3c743d7d7c..af465be505 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 32;
+use Test::More tests => 35;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -121,6 +121,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.21.0

From 938a50703283eaf8983ca33739eea308248d8587 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 18:02:59 +1100
Subject: [PATCH 5/8] New read-only target_session_attrs type

With this read-only option type, application can connect
to a read-only server in the list of hosts, in case
if there is no read-only server available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  7 +++++-
 src/interfaces/libpq/fe-connect.c     | 34 ++++++++++++++++++++-------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 10 +++++++-
 5 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 67f2c6a5c1..2be51b2a49 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1677,6 +1677,11 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
         configuration parameter that is reported by the server upon successful connection.
        </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default.
+       </para>
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 59ee803340..3217ae0303 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1300,6 +1300,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3494,8 +3496,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write or prefer-read connection is required, see
-				 * if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3532,7 +3534,8 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3592,17 +3595,28 @@ keep_going:						/* We will come back to here until there is
 
 				/*
 				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
+					/*
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
+					 */
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
+
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3690,12 +3704,14 @@ keep_going:						/* We will come back to here until there is
 					 * ignore it. Server is read-write and requested mode is
 					 * prefer-read, record it for the first time and try to
 					 * consume in the next scan (it means no read-only server
-					 * is found in the first scan).
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
 					 */
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/*
 						 * The following scenario is possible only for the
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index f3833678e2..a015579c43 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -75,7 +75,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 4e8bab3822..a00d8bddeb 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,7 +366,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index af465be505..ac1e11e1ab 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 35;
+use Test::More tests => 37;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -133,6 +133,14 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.21.0

From 650ebafc126f4f77fa039c07553498fd3e6d2db1 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 10 Apr 2019 23:19:09 +1000
Subject: [PATCH 6/8] Primary, prefer-standby and standby options

New options to check whether the server is in recovery mode
or not, before considering them to connect. To confirm whether
the server is running in recovery mode or not, it sends the query
to server as 'SELECT pg_is_in_recovery()'.
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 236 +++++++++++++++++++++++---
 src/interfaces/libpq/libpq-fe.h       |   8 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 262 insertions(+), 30 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 2be51b2a49..6b84accd08 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1682,6 +1683,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         If this parameter is set to <literal>read-only</literal>, only a connection
         in which read-only transactions are accepted by default.
        </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        where the server is not in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, only a connection in which
+        where the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        where the server is in recovery mode.
+       </para>
+
+       <para>
+        To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
+        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
+        is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 3217ae0303..59efaa5133 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -124,6 +124,7 @@ static int	ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #define DefaultOption	""
 #define DefaultAuthtype		  ""
 #define DefaultTargetSessionAttrs	"any"
+#define DefaultTargetServerType	"any"
 #ifdef USE_SSL
 #define DefaultSSLMode "prefer"
 #else
@@ -340,7 +341,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1302,6 +1303,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2196,6 +2203,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2235,19 +2243,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means, failed to connect to read-only servers
 				 * and now try connect to read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3504,7 +3512,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3547,7 +3557,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
 						/* Append error report to conn->errorMessage. */
@@ -3578,8 +3588,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3594,30 +3604,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * severs before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
 				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
+				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3719,7 +3769,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
@@ -3754,8 +3804,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3808,6 +3858,144 @@ keep_going:						/* We will come back to here until there is
 				goto keep_going;
 			}
 
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is not in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3953,7 +4141,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index a015579c43..6c5780c672 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	 CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -76,7 +77,10 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index a00d8bddeb..740033e116 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -366,7 +366,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -410,7 +410,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index ac1e11e1ab..8fa28dab23 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 37;
+use Test::More tests => 41;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -141,6 +141,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.21.0

From c58ace1fb9356ccab5b2c9f7fcbb1bf665da9960 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 18:11:18 +1100
Subject: [PATCH 7/8] New function to rejecting the checked write connection

When the connection is checked for write or not and based
on the result, if we decide to reject it, call the newly
added function to reject it.
---
 src/interfaces/libpq/fe-connect.c | 123 ++++++++++++------------------
 1 file changed, 47 insertions(+), 76 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 59efaa5133..529985ea0c 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2121,6 +2121,51 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+static void
+reject_checked_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3547,10 +3592,6 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
@@ -3560,42 +3601,7 @@ keep_going:						/* We will come back to here until there is
 						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3776,42 +3782,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
-- 
2.21.0

From f6a62b5a53c16ab793ff5ada2d6fd06d39d9e04a Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 28 Mar 2019 15:30:01 +1100
Subject: [PATCH 8/8] Server recovery mode handling

in_recovery GUC_REPORT is added to update the clients when the
server is recovery mode, this is useful for the client connections
to connect to a standby server with a faster check instead of
executing a command.

New SIGUSR1 handling interrupt is added to support reporting
of recovery mode exit to all backends and their respective
clients.

Some parts of the code is taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.
---
 doc/src/sgml/libpq.sgml              |  14 ++-
 doc/src/sgml/protocol.sgml           |   8 +-
 src/backend/access/transam/xlog.c    |   3 +
 src/backend/commands/async.c         |   1 -
 src/backend/storage/ipc/procarray.c  |  28 ++++++
 src/backend/storage/ipc/procsignal.c |   3 +
 src/backend/storage/ipc/standby.c    |   9 ++
 src/backend/tcop/postgres.c          |  60 ++++++++++++
 src/backend/utils/init/postinit.c    |   6 +-
 src/backend/utils/misc/check_guc     |   2 +-
 src/backend/utils/misc/guc.c         |  17 +++-
 src/include/storage/procarray.h      |   1 +
 src/include/storage/procsignal.h     |   2 +
 src/include/storage/standby.h        |   1 +
 src/include/tcop/tcopprot.h          |   2 +
 src/interfaces/libpq/fe-connect.c    | 133 +++++++++++++++++----------
 src/interfaces/libpq/fe-exec.c       |   4 +
 src/interfaces/libpq/libpq-int.h     |   1 +
 18 files changed, 234 insertions(+), 61 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 6b84accd08..90e8c96820 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1702,8 +1702,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
-        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
-        is in recovery mode.
+        will be sent upon any successful connection if the server is prior to version 12; if it returns
+        <literal>t</literal>, it means server is in recovery mode. But for server version 12 or greater
+        uses the value of <varname>in_recovery</varname> configuration parameter that is reported by the
+        server upon successful connection.
        </para>
 
       </listitem>
@@ -2071,15 +2073,17 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
        <varname>integer_datetimes</varname>,
-       <varname>standard_conforming_strings</varname>, and
-       <varname>transaction_read_only</varname>.
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before 9.0;
-       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 05286c7365..9ed2a03b73 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1284,15 +1284,17 @@ SELECT 1/0;
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
     <varname>integer_datetimes</varname>,
-    <varname>standard_conforming_strings</varname>, and
-    <varname>transaction_read_only</varname>.
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before 9.0;
-    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+    were not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 13e0d2366f..622b0870af 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7766,6 +7766,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryInProgress = false;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 738e6ec7e2..102094e765 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -1736,7 +1736,6 @@ ProcessNotifyInterrupt(void)
 		ProcessIncomingNotify();
 }
 
-
 /*
  * Read all pending notifications from the queue, and deliver appropriate
  * ones to my frontend.  Stop when we reach queue head or an uncommitted
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 18a0f62ba6..ad72ab10c7 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2972,6 +2972,34 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 	return true;				/* timed out, still conflicts */
 }
 
+/*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
 /*
  * ProcArraySetReplicationSlotXmin
  *
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7605b2c367..e4548dc323 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,6 +292,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 25b7e314af..d55366af4e 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -138,6 +138,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 44a59e1d4f..33511a9433 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -167,6 +167,15 @@ static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
 static StringInfoData row_description_buf;
@@ -195,6 +204,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -543,6 +553,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -2954,6 +2968,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 	errno = save_errno;
 }
 
+/*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
 /*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index e9f72b5069..29a159dc11 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -651,7 +651,11 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		 * This is handled by calling RecoveryInProgress and ignoring the
 		 * result.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index d228bbed68..1c0f51ac8b 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_int \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 5357e51d3f..719ea6fc24 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -581,7 +581,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
-
+static bool in_recovery;
 
 /* should be static, but commands/variable.c needs to get at this */
 char	   *role_string;
@@ -1770,6 +1770,21 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"allow_system_table_mods", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index da8b672096..86f0c13134 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
 									  int nxids, const TransactionId *xids,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 05b186a05c..9cf9560b06 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index a3f8f82ff3..2c73f0c0a8 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index ec21f7e45c..ed21a9e2f2 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -66,6 +66,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 529985ea0c..82d952eafc 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2166,6 +2166,49 @@ reject_checked_write_connection(PGconn *conn)
 	conn->try_next_host = true;
 }
 
+static void
+reject_checked_recovery_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3619,27 +3662,52 @@ keep_going:						/* We will come back to here until there is
 						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
 						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
 
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_RECOVERY;
+
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
 					}
+					else if ((conn->in_recovery &&
+							  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+							 (!conn->in_recovery &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_target_connection;
 
-					conn->status = CONNECTION_CHECK_RECOVERY;
+						reject_checked_recovery_connection(conn);
+						goto keep_going;
+					}
 
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
 				/*
@@ -3888,40 +3956,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is not in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record primary host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_recovery_connection(conn);
 						goto keep_going;
 					}
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 701c4a66fe..7cffed57cd 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1117,6 +1117,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	{
 		conn->transaction_read_only = (strcmp(value, "on") == 0);
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 740033e116..7b36ddb804 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -443,6 +443,7 @@ struct pg_conn
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
 	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.21.0

From 30fbb4a913697fe35a195dd41ddd5bcfeec53c0e Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Fri, 6 Sep 2019 16:26:01 -0400
Subject: [PATCH] Restructure the code to remove duplicate code

The duplicate code logic of checking for the server version
before issuing the SHOW transaction_read_only to find out whether
the server is read-write or not is restructured under a new
connection status, so that duplicate code is removed. This is
required for the next set of patches

Author: Hari Babu Kommi
Discussion: https://postgr.es/m/CAJrrPGe_qgdbbN+yBgEVpd+YLHXXjTruzk6RmTMhqrFig+32ag@mail.gmail.com
---
 src/interfaces/libpq/fe-connect.c | 87 ++++++++++++-------------------
 src/interfaces/libpq/libpq-fe.h   |  3 +-
 2 files changed, 34 insertions(+), 56 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index f03d43376c..91316709a5 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3434,6 +3434,13 @@ keep_going:						/* We will come back to here until there is
 					return PGRES_POLLING_WRITING;
 				}
 
+				/* Almost there now ... */
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
+			}
+
+		case CONNECTION_CHECK_TARGET:
+			{
 				/*
 				 * If a read-write connection is required, see if we have one.
 				 *
@@ -3476,67 +3483,37 @@ keep_going:						/* We will come back to here until there is
 			}
 
 		case CONNECTION_SETENV:
-
-			/*
-			 * Do post-connection housekeeping (only needed in protocol 2.0).
-			 *
-			 * We pretend that the connection is OK for the duration of these
-			 * queries.
-			 */
-			conn->status = CONNECTION_OK;
-
-			switch (pqSetenvPoll(conn))
 			{
-				case PGRES_POLLING_OK:	/* Success */
-					break;
-
-				case PGRES_POLLING_READING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_READING;
-
-				case PGRES_POLLING_WRITING: /* Still going */
-					conn->status = CONNECTION_SETENV;
-					return PGRES_POLLING_WRITING;
-
-				default:
-					goto error_return;
-			}
-
-			/*
-			 * If a read-write connection is required, see if we have one.
-			 * (This should match the stanza in the CONNECTION_AUTH_OK case
-			 * above.)
-			 *
-			 * Servers before 7.4 lack the transaction_read_only GUC, but by
-			 * the same token they don't have any read-only mode, so we may
-			 * just skip the test in that case.
-			 */
-			if (conn->sversion >= 70400 &&
-				conn->target_session_attrs != NULL &&
-				strcmp(conn->target_session_attrs, "read-write") == 0)
-			{
-				if (!saveErrorMessage(conn, &savedMessage))
-					goto error_return;
-
+				/*
+				 * Do post-connection housekeeping (only needed in protocol 2.0).
+				 *
+				 * We pretend that the connection is OK for the duration of these
+				 * queries.
+				 */
 				conn->status = CONNECTION_OK;
-				if (!PQsendQuery(conn,
-								 "SHOW transaction_read_only"))
+
+				switch (pqSetenvPoll(conn))
 				{
-					restoreErrorMessage(conn, &savedMessage);
-					goto error_return;
+					case PGRES_POLLING_OK:	/* Success */
+						break;
+
+					case PGRES_POLLING_READING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_READING;
+
+					case PGRES_POLLING_WRITING: /* Still going */
+						conn->status = CONNECTION_SETENV;
+						return PGRES_POLLING_WRITING;
+
+					default:
+						goto error_return;
 				}
-				conn->status = CONNECTION_CHECK_WRITABLE;
-				restoreErrorMessage(conn, &savedMessage);
-				return PGRES_POLLING_READING;
+
+				/* Almost there now ... */
+				conn->status = CONNECTION_CHECK_TARGET;
+				goto keep_going;
 			}
 
-			/* We can release the address list now. */
-			release_conn_addrinfo(conn);
-
-			/* We are open for business! */
-			conn->status = CONNECTION_OK;
-			return PGRES_POLLING_OK;
-
 		case CONNECTION_CONSUME:
 			{
 				conn->status = CONNECTION_OK;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 22c4954f2b..5f65db30e4 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -67,7 +67,8 @@ typedef enum
 								 * connection. */
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
-	CONNECTION_GSS_STARTUP		/* Negotiating GSSAPI. */
+	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
+	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
 typedef enum
-- 
2.17.1

From 9399e3f7f5e85f41871d4e586b0582f697380c0b Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Tue, 10 Sep 2019 12:48:28 -0300
Subject: [PATCH v13 2/8] doc change

---
 doc/src/sgml/libpq.sgml | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 5601485555..23bf1ea632 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1647,17 +1647,27 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
      <varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
       <term><literal>target_session_attrs</literal></term>
       <listitem>
+       <para>
+        The supported options for this parameter are, <literal>any</literal> and
+        <literal>read-write</literal>. The default value of this parameter,
+        <literal>any</literal>, regards all connections as acceptable.
+        If multiple hosts were specified in the connection string, based on the
+        specified value, any remaining servers will be tried before confirming
+        succesful connection or failure.
+       </para>
+
        <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        To find out whether the server supports read-write transactions are not,
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection; if it returns <literal>on</literal>, it means server
+        doesn't support read-write transactions.
+       </para>
       </listitem>
     </varlistentry>
     </variablelist>
-- 
2.17.1

From 247e888266882ab673efd04ecf017846400859ad Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Feb 2019 11:50:33 +1100
Subject: [PATCH v13 1/8] New TargetSessionAttrsType enum

This new enum is useful to compare the requested session type
instead of comparing it with string always. This may not show
much improvement with current code, but it will be useful with
further patches
---
 src/interfaces/libpq/fe-connect.c | 12 ++++++++----
 src/interfaces/libpq/libpq-fe.h   |  6 ++++++
 src/interfaces/libpq/libpq-int.h  |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 8ba0159313..f104fd48aa 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1295,8 +1295,11 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -3449,8 +3452,7 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
 					/*
 					 * Save existing error messages across the PQsendQuery
@@ -3791,6 +3793,8 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 5f65db30e4..0612e68c62 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -71,6 +71,12 @@ typedef enum
 	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
 } ConnStatusType;
 
+typedef enum
+{
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE		/* Read-write session */
+}			TargetSessionAttrsType;
+
 typedef enum
 {
 	PGRES_POLLING_FAILED = 0,
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index d37bb3ce40..20791b5b73 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -367,6 +367,7 @@ struct pg_conn
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
-- 
2.17.1

From c0b48576c961ed0c0304ac5c83363acf6a51f818 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:05:24 +1100
Subject: [PATCH v13 3/8] Make transaction_read_only as GUC_REPORT variable

transaction_read_only GUC variable value is used in multi host
connection to identify the required host of read-write, but currently
this carried out by executing a command to find out whether the host
is a read-write or not? Instead of that, Reporting the GUC to the client
upon connection reduces the time to make the connection.
---
 doc/src/sgml/libpq.sgml           | 14 ++++---
 doc/src/sgml/protocol.sgml        |  8 ++--
 src/backend/utils/misc/guc.c      |  2 +-
 src/interfaces/libpq/fe-connect.c | 70 +++++++++++++++++++++++--------
 src/interfaces/libpq/fe-exec.c    |  6 ++-
 src/interfaces/libpq/libpq-int.h  |  1 +
 6 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 23bf1ea632..edda94196b 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1665,8 +1665,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, it means server
-        doesn't support read-write transactions.
+        successful connection if the server is prior to version 12; if it returns
+        <literal>on</literal>, it means server doesn't support read-write transactions.
+        But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
+        configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
     </varlistentry>
@@ -1977,14 +1979,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 80275215e0..dbf12fcc46 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELECT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 90ffd89339..3c47473bcd 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1543,7 +1543,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index f104fd48aa..abac93d6da 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3454,26 +3454,61 @@ keep_going:						/* We will come back to here until there is
 				if (conn->sversion >= 70400 &&
 					conn->requested_session_type != SESSION_TYPE_ANY)
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
-
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have tried
+						 * and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if (conn->transaction_read_only)
+					{
+						/* Not writable; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext("could not make a writable "
+														"connection to server "
+														"\"%s:%s\"\n"),
+										  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
 				}
 
 				/* We can release the address list now. */
@@ -3786,6 +3821,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index b3c59a0992..3c17100e05 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 20791b5b73..7d26b94f9f 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -432,6 +432,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.17.1

From 2dee9b996ed8f242ceb5d0f1924a9c0455620e53 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 17:56:48 +1100
Subject: [PATCH v13 4/8] New prefer-read target_session_attrs type

With this prefer-read option type, application can prefer
connecting to a read-only server if available from the list
of hosts, otherwise connect it to read-write server
---
 doc/src/sgml/libpq.sgml               |  21 ++--
 src/interfaces/libpq/fe-connect.c     | 161 ++++++++++++++++++++++----
 src/interfaces/libpq/libpq-fe.h       |   3 +-
 src/interfaces/libpq/libpq-int.h      |  13 ++-
 src/test/recovery/t/001_stream_rep.pl |  14 ++-
 5 files changed, 177 insertions(+), 35 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index edda94196b..29f9ae5c78 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1648,12 +1648,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        The supported options for this parameter are, <literal>any</literal> and
-        <literal>read-write</literal>. The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-        If multiple hosts were specified in the connection string, based on the
-        specified value, any remaining servers will be tried before confirming
-        succesful connection or failure.
+        The supported options for this parameter are, <literal>any</literal>,
+        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts were specified in the
+        connection string, based on the specified value, any remaining servers
+        will be tried before confirming succesful connection or failure.
        </para>
 
        <para>
@@ -1662,6 +1662,13 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         is considered acceptable.
        </para>
 
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, only a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions accepted will be considered.
+       </para>
+
        <para>
         To find out whether the server supports read-write transactions are not,
         query <literal>SHOW transaction_read_only</literal> will be sent upon any
@@ -1671,7 +1678,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         configuration parameter that is reported by the server upon successful connection.
        </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index abac93d6da..8673b8e903 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -341,7 +341,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1299,6 +1299,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_ANY;
 		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2232,13 +2234,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means, failed to connect to read-only servers
+				 * and now try connect to read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3445,7 +3465,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write or prefer-read connection is required, see
+				 * if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3460,8 +3481,8 @@ keep_going:						/* We will come back to here until there is
 						 * Save existing error messages across the PQsendQuery
 						 * attempt.  This is necessary because PQsendQuery is
 						 * going to reset conn->errorMessage, so we would lose
-						 * error messages related to previous hosts we have tried
-						 * and failed to connect to.
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
 						 */
 						if (!saveErrorMessage(conn, &savedMessage))
 							goto error_return;
@@ -3473,16 +3494,30 @@ keep_going:						/* We will come back to here until there is
 							restoreErrorMessage(conn, &savedMessage);
 							goto error_return;
 						}
+
 						conn->status = CONNECTION_CHECK_WRITABLE;
+
 						restoreErrorMessage(conn, &savedMessage);
 						return PGRES_POLLING_READING;
 					}
-					else if (conn->transaction_read_only)
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
 						const char *displayed_port;
 
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3492,16 +3527,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3509,8 +3556,36 @@ keep_going:						/* We will come back to here until there is
 						conn->try_next_host = true;
 						goto keep_going;
 					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+					conn->read_write_host_index != -2)
+				{
+					/* Close connection politely. */
+					conn->status = CONNECTION_OK;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
+				}
+
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3608,11 +3683,33 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan).
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3625,16 +3722,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3643,7 +3752,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3830,6 +3940,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 0612e68c62..563f8b98ce 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -74,7 +74,8 @@ typedef enum
 typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
-	SESSION_TYPE_READ_WRITE		/* Read-write session */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 7d26b94f9f..174f370818 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -365,7 +365,10 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read.
+	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
 
@@ -402,6 +405,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 3c743d7d7c..af465be505 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 32;
+use Test::More tests => 35;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -121,6 +121,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.17.1

From 356b5c8969b04bd29c69de888efe5ab1cd8e3e3d Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 27 Mar 2019 18:02:59 +1100
Subject: [PATCH v13 5/8] New read-only target_session_attrs type

With this read-only option type, application can connect
to a read-only server in the list of hosts, in case
if there is no read-only server available, the connection
attempt fails.
---
 doc/src/sgml/libpq.sgml               |  7 +++++-
 src/interfaces/libpq/fe-connect.c     | 34 ++++++++++++++++++++-------
 src/interfaces/libpq/libpq-fe.h       |  3 ++-
 src/interfaces/libpq/libpq-int.h      |  2 +-
 src/test/recovery/t/001_stream_rep.pl | 10 +++++++-
 5 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 29f9ae5c78..3a1071e408 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal> and <literal>prefer-read</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1677,6 +1677,11 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         But for server version 12 or greater uses the value of <varname>transaction_read_only</varname>
         configuration parameter that is reported by the server upon successful connection.
        </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default.
+       </para>
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 8673b8e903..e660675808 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1301,6 +1301,8 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
 		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -3465,8 +3467,8 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write or prefer-read connection is required, see
-				 * if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
@@ -3503,7 +3505,8 @@ keep_going:						/* We will come back to here until there is
 					else if ((conn->transaction_read_only &&
 							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 							 (!conn->transaction_read_only &&
-							  conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/* Not a requested type; fail this connection. */
 						const char *displayed_host;
@@ -3563,17 +3566,28 @@ keep_going:						/* We will come back to here until there is
 
 				/*
 				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
 				 */
-				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-					conn->read_write_host_index != -2)
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
+					/*
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
+					 */
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
+
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->read_write_host_index == -1)
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
 						conn->read_write_host_index = conn->whichhost;
 
 					/*
@@ -3693,12 +3707,14 @@ keep_going:						/* We will come back to here until there is
 					 * ignore it. Server is read-write and requested mode is
 					 * prefer-read, record it for the first time and try to
 					 * consume in the next scan (it means no read-only server
-					 * is found in the first scan).
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
 					 */
 					if ((readonly_server &&
 						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
 						(!readonly_server &&
-						 conn->requested_session_type == SESSION_TYPE_PREFER_READ))
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
 						/*
 						 * The following scenario is possible only for the
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 563f8b98ce..fc0178cd5d 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -75,7 +75,8 @@ typedef enum
 {
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
-	SESSION_TYPE_PREFER_READ	/* Prefer read only session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 174f370818..e3c15b2ba8 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -367,7 +367,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read.
+	 * prefer-read and read-only.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index af465be505..ac1e11e1ab 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 35;
+use Test::More tests => 37;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -133,6 +133,14 @@ test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 test_target_session_attrs($node_master, $node_master, $node_master,
 	"prefer-read", 0);
 
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.17.1

From 9e551ce44a04a4646518c66aee146e4fc7c0c0f9 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Wed, 10 Apr 2019 23:19:09 +1000
Subject: [PATCH v13 6/8] Primary, prefer-standby and standby options

New options to check whether the server is in recovery mode
or not, before considering them to connect. To confirm whether
the server is running in recovery mode or not, it sends the query
to server as 'SELECT pg_is_in_recovery()'.
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 236 +++++++++++++++++++++++---
 src/interfaces/libpq/libpq-fe.h       |   8 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 262 insertions(+), 30 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 3a1071e408..e447e8fad7 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1649,7 +1649,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are, <literal>any</literal>,
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts were specified in the
         connection string, based on the specified value, any remaining servers
@@ -1682,6 +1683,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         If this parameter is set to <literal>read-only</literal>, only a connection
         in which read-only transactions are accepted by default.
        </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        where the server is not in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, only a connection in which
+        where the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        where the server is in recovery mode.
+       </para>
+
+       <para>
+        To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
+        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
+        is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index e660675808..2e1872795a 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -125,6 +125,7 @@ static int	ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #define DefaultOption	""
 #define DefaultAuthtype		  ""
 #define DefaultTargetSessionAttrs	"any"
+#define DefaultTargetServerType	"any"
 #ifdef USE_SSL
 #define DefaultSSLMode "prefer"
 #else
@@ -341,7 +342,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1303,6 +1304,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2197,6 +2204,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2236,19 +2244,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means, failed to connect to read-only servers
 				 * and now try connect to read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3475,7 +3483,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 120000)
 					{
@@ -3518,7 +3528,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
 						/* Append error report to conn->errorMessage. */
@@ -3549,8 +3559,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3565,30 +3575,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * severs before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
 				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
+				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3722,7 +3772,7 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
@@ -3757,8 +3807,8 @@ keep_going:						/* We will come back to here until there is
 
 						/* Record read-write host index */
 						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3811,6 +3861,144 @@ keep_going:						/* We will come back to here until there is
 				goto keep_going;
 			}
 
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("server is not in recovery mode "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3956,7 +4144,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index fc0178cd5d..30b181aa37 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	 CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -76,7 +77,10 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
 }			TargetSessionAttrsType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index e3c15b2ba8..d9e38558c4 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -367,7 +367,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -411,7 +411,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index ac1e11e1ab..8fa28dab23 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 37;
+use Test::More tests => 41;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -141,6 +141,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
2.17.1

From 599bcd4c876065f06489de5820211d42ab3b6ece Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Mon, 25 Mar 2019 18:11:18 +1100
Subject: [PATCH v13 7/8] New function to rejecting the checked write
 connection

When the connection is checked for write or not and based
on the result, if we decide to reject it, call the newly
added function to reject it.
---
 src/interfaces/libpq/fe-connect.c | 123 ++++++++++++------------------
 1 file changed, 47 insertions(+), 76 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 2e1872795a..f9075d2c10 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2122,6 +2122,51 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+static void
+reject_checked_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3518,10 +3563,6 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
@@ -3531,42 +3572,7 @@ keep_going:						/* We will come back to here until there is
 						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3779,42 +3785,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_write_connection(conn);
 						goto keep_going;
 					}
 
-- 
2.17.1

From 820e747f91a0d57d5018519f59a148fb50249b57 Mon Sep 17 00:00:00 2001
From: Hari Babu <kommi.haribabu@gmail.com>
Date: Thu, 28 Mar 2019 15:30:01 +1100
Subject: [PATCH v13 8/8] Server recovery mode handling

in_recovery GUC_REPORT is added to update the clients when the
server is recovery mode, this is useful for the client connections
to connect to a standby server with a faster check instead of
executing a command.

New SIGUSR1 handling interrupt is added to support reporting
of recovery mode exit to all backends and their respective
clients.

Some parts of the code is taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.
---
 doc/src/sgml/libpq.sgml              |  14 ++-
 doc/src/sgml/protocol.sgml           |   8 +-
 src/backend/access/transam/xlog.c    |   3 +
 src/backend/storage/ipc/procarray.c  |  28 ++++++
 src/backend/storage/ipc/procsignal.c |   3 +
 src/backend/storage/ipc/standby.c    |   9 ++
 src/backend/tcop/postgres.c          |  60 ++++++++++++
 src/backend/utils/init/postinit.c    |   6 +-
 src/backend/utils/misc/check_guc     |   2 +-
 src/backend/utils/misc/guc.c         |  16 ++++
 src/include/storage/procarray.h      |   1 +
 src/include/storage/procsignal.h     |   2 +
 src/include/storage/standby.h        |   1 +
 src/include/tcop/tcopprot.h          |   2 +
 src/interfaces/libpq/fe-connect.c    | 135 +++++++++++++++++----------
 src/interfaces/libpq/fe-exec.c       |   4 +
 src/interfaces/libpq/libpq-int.h     |   1 +
 17 files changed, 235 insertions(+), 60 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index e447e8fad7..dc1e89bb2a 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1702,8 +1702,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         To find out whether the server is in recovery mode or not, query <literal>SELECT pg_is_in_recovery()</literal>
-        will be sent upon any successful connection; if it returns <literal>t</literal>, means server
-        is in recovery mode.
+        will be sent upon any successful connection if the server is prior to version 12; if it returns
+        <literal>t</literal>, it means server is in recovery mode. But for server version 12 or greater
+        uses the value of <varname>in_recovery</varname> configuration parameter that is reported by the
+        server upon successful connection.
        </para>
 
       </listitem>
@@ -2016,15 +2018,17 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
        <varname>integer_datetimes</varname>,
-       <varname>standard_conforming_strings</varname>, and
-       <varname>transaction_read_only</varname>.
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before 9.0;
-       <varname>transaction_read_only</varname> was not reported by release before 12.0.)
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by release before 12.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index dbf12fcc46..58142c072d 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1284,15 +1284,17 @@ SELECT 1/0;
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
     <varname>integer_datetimes</varname>,
-    <varname>standard_conforming_strings</varname>, and
-    <varname>transaction_read_only</varname>.
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before 9.0;
-    <varname>transaction_read_only</varname> was not reported by releases before 12.0.)
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+    were not reported by releases before 12.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 6876537b62..5093fd183a 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7769,6 +7769,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryInProgress = false;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 8abcfdf841..744475cc2c 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2970,6 +2970,34 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 	return true;				/* timed out, still conflicts */
 }
 
+/*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
 /*
  * ProcArraySetReplicationSlotXmin
  *
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7605b2c367..e4548dc323 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,6 +292,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 01ddffec40..b0e88ee545 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -138,6 +138,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index e8d8e6f828..69ce3ec786 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -167,6 +167,15 @@ static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
 static StringInfoData row_description_buf;
@@ -195,6 +204,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -543,6 +553,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -2961,6 +2975,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 	errno = save_errno;
 }
 
+/*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
 /*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 29c5ec7b58..59fb4e905b 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -649,7 +649,11 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		 * This is handled by calling RecoveryInProgress and ignoring the
 		 * result.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index 416a0875b6..a4ebcef614 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_num \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 3c47473bcd..aacaecc520 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -580,6 +580,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
+static bool in_recovery;
 
 
 /* should be static, but commands/variable.c needs to get at this */
@@ -1769,6 +1770,21 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"allow_system_table_mods", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index da8b672096..86f0c13134 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
 									  int nxids, const TransactionId *xids,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 05b186a05c..9cf9560b06 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index a3f8f82ff3..2c73f0c0a8 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index ec21f7e45c..ed21a9e2f2 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -66,6 +66,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index f9075d2c10..585339b537 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2167,6 +2167,49 @@ reject_checked_write_connection(PGconn *conn)
 	conn->try_next_host = true;
 }
 
+static void
+reject_checked_recovery_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3590,27 +3633,52 @@ keep_going:						/* We will come back to here until there is
 						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
 						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
 
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					if (conn->sversion < 120000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_RECOVERY;
+
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
+					}
+					else if ((conn->in_recovery &&
+							  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+							 (!conn->in_recovery &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_target_connection;
+
+						reject_checked_recovery_connection(conn);
+						goto keep_going;
 					}
 
-					conn->status = CONNECTION_CHECK_RECOVERY;
-
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
 				/*
@@ -3891,40 +3959,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is not in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record primary host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_recovery_connection(conn);
 						goto keep_going;
 					}
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 3c17100e05..a964483eee 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1117,6 +1117,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	{
 		conn->transaction_read_only = (strcmp(value, "on") == 0);
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index d9e38558c4..436109b41c 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -444,6 +444,7 @@ struct pg_conn
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
 	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
2.17.1

From 74cad19872e70ffe937ad582fab30bb8f17f7a16 Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Mon, 30 Sep 2019 11:55:57 +1000
Subject: [PATCH v14 1/3] Enhance libpq target_session_attrs:
 read-write/prefer-read/read-only

Improve checking of the requested target session type, to avoid always having to do string
comparisons on target_session_attrs.
Make "transaction_read_only" a GUC_REPORT variable, to avoid having to execute a query
post-connection in order to determine whether a host is read-write (and reduce time to make the
connection).
Add new "prefer-read" target_session_attrs option value, to support connecting to a read-only
server if available from the list of hosts (otherwise connect to a read-write server).
Add new "read-only" target_session_attrs option value, to support connecting to a read-only
server if available from the list of hosts (otherwise the connection attempt fails).

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 doc/src/sgml/libpq.sgml               |  54 ++++++--
 doc/src/sgml/protocol.sgml            |   8 +-
 src/backend/utils/misc/guc.c          |   2 +-
 src/interfaces/libpq/fe-connect.c     | 239 +++++++++++++++++++++++++++++-----
 src/interfaces/libpq/fe-exec.c        |   6 +-
 src/interfaces/libpq/libpq-fe.h       |   8 ++
 src/interfaces/libpq/libpq-int.h      |  15 ++-
 src/test/recovery/t/001_stream_rep.pl |  22 +++-
 8 files changed, 299 insertions(+), 55 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c58527b..0d3edfc 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1674,18 +1674,46 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
+        The supported options for this parameter are <literal>any</literal>,
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts are specified in the
+        connection string, each host is tried in the order given until a connection
+        is successful.
+       </para>
+
+       <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions are accepted will be considered.
+       </para>
+
+       <para>
+        To determine whether the server supports read-write transactions, the
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection, if the server is prior to version 13; if it returns
+        <literal>on</literal>, it means the server doesn't support read-write
+        transactions.
+        If the server is version 13 or greater, the support of read-write
+        transactions is determined by the value of the
+        <varname>transaction_read_only</varname> configuration parameter that is
+        reported by the server upon successful connection.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default is considered
+        acceptable.
+       </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
@@ -1993,14 +2021,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 8027521..87b95bc 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELECT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 2178e1c..c64ec03 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1543,7 +1543,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index f91f0f2..7058f5d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -350,7 +350,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1327,8 +1327,15 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -2261,13 +2268,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means we failed to connect to read-only servers
+				 * and should now try to connect to a read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3474,38 +3499,139 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
+				{
+					if (conn->sversion < 130000)
+					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_WRITABLE;
+
+						restoreErrorMessage(conn, &savedMessage);
+						return PGRES_POLLING_READING;
+					}
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
+					{
+						/* Not a requested type; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
 					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
 					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
 
+					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
-					{
-						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
-					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3604,11 +3730,35 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3621,16 +3771,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3639,7 +3801,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3817,6 +3980,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
@@ -3824,6 +3988,9 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index b3c59a0..3c17100 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 5f65db3..aa6f22f 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -73,6 +73,14 @@ typedef enum
 
 typedef enum
 {
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
+} TargetSessionAttrsType;
+
+typedef enum
+{
 	PGRES_POLLING_FAILED = 0,
 	PGRES_POLLING_READING,		/* These two indicate that one may	  */
 	PGRES_POLLING_WRITING,		/* use select before polling again.   */
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 64468ab..eb687d8 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -367,8 +367,12 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read and read-only.
+	 */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
@@ -403,6 +407,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
@@ -433,6 +445,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 3c743d7..ac1e11e 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 32;
+use Test::More tests => 37;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -121,6 +121,26 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1

From 6ce04730b7fcc6fa532cbae3a2c149e3da6ae03c Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Mon, 30 Sep 2019 15:45:46 +1000
Subject: [PATCH v14 3/3] Server recovery mode handling

Add "in_recovery" as a GUC_REPORT variable, to update clients when the
server is in recovery mode. This improves the speed of client connections
to a standby server, by avoiding the need to execute a command to
determine if the server is in recovery mode.
Add new SIGUSR1 handling interrupt to support reporting of recovery mode
exit to all backends and their respective clients.
Some parts of the code is taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 doc/src/sgml/libpq.sgml              |  16 ++--
 doc/src/sgml/protocol.sgml           |   8 +-
 src/backend/access/transam/xlog.c    |   3 +
 src/backend/storage/ipc/procarray.c  |  28 +++++++
 src/backend/storage/ipc/procsignal.c |   3 +
 src/backend/storage/ipc/standby.c    |   9 +++
 src/backend/tcop/postgres.c          |  60 +++++++++++++++
 src/backend/utils/init/postinit.c    |   6 +-
 src/backend/utils/misc/check_guc     |   2 +-
 src/backend/utils/misc/guc.c         |  16 ++++
 src/include/storage/procarray.h      |   1 +
 src/include/storage/procsignal.h     |   2 +
 src/include/storage/standby.h        |   1 +
 src/include/tcop/tcopprot.h          |   2 +
 src/interfaces/libpq/fe-connect.c    | 142 +++++++++++++++++++++++------------
 src/interfaces/libpq/fe-exec.c       |   4 +
 src/interfaces/libpq/libpq-int.h     |   1 +
 17 files changed, 245 insertions(+), 59 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 5f31fd0..9f66fb8 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1732,8 +1732,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         To determine whether the server is in recovery mode, the query
-        <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful connection;
-        if it returns <literal>t</literal>, it means the server is in recovery mode.
+        <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful connection
+        if the server is prior to version 13; if it returns <literal>t</literal>, it means the server
+        is in recovery mode.
+        If the server is version 13 or greater, the recovery mode state is determined by the value of
+        the <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection.
        </para>
 
       </listitem>
@@ -2046,15 +2050,17 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
        <varname>integer_datetimes</varname>,
-       <varname>standard_conforming_strings</varname>, and
-       <varname>transaction_read_only</varname>.
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before 9.0;
-       <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by releases before 13.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 87b95bc..df3953f 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1284,15 +1284,17 @@ SELECT 1/0;
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
     <varname>integer_datetimes</varname>,
-    <varname>standard_conforming_strings</varname>, and
-    <varname>transaction_read_only</varname>.
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before 9.0;
-    <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+    were not reported by releases before 13.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 6c69eb6..4fe506e 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7770,6 +7770,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryInProgress = false;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 8abcfdf..744475c 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2971,6 +2971,34 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 }
 
 /*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
+/*
  * ProcArraySetReplicationSlotXmin
  *
  * Install limits to future computations of the xmin horizon to prevent vacuum
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7605b2c..e4548dc 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,6 +292,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 01ddffe..b0e88ee 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -138,6 +138,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index e8d8e6f..69ce3ec 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -167,6 +167,15 @@ static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
 static StringInfoData row_description_buf;
@@ -195,6 +204,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -543,6 +553,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -2962,6 +2976,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 }
 
 /*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
+/*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
  * If an interrupt condition is pending, and it's safe to service it,
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 29c5ec7..59fb4e9 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -649,7 +649,11 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		 * This is handled by calling RecoveryInProgress and ignoring the
 		 * result.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index 416a087..a4ebcef 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_num \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index c64ec03..633bc2d 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -580,6 +580,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
+static bool in_recovery;
 
 
 /* should be static, but commands/variable.c needs to get at this */
@@ -1770,6 +1771,21 @@ static struct config_bool ConfigureNamesBool[] =
 	},
 
 	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"allow_system_table_mods", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
 			NULL,
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index da8b672..86f0c13 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
 									  int nxids, const TransactionId *xids,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 05b186a..9cf9560 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index a3f8f82..2c73f0c 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index ec21f7e..ed21a9e 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -66,6 +66,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 0c096d1..7a04618 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2207,6 +2207,58 @@ reject_checked_read_or_write_connection(PGconn *conn)
 	conn->try_next_host = true;
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested session type (for recovery). The connection state
+ * is set to try the next host (if any).
+ * In the case of SESSION_TYPE_PREFER_STANDBY, if the read-write-or-primary host-index
+ * hasn't been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+reject_checked_recovery_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3630,27 +3682,52 @@ keep_going:						/* We will come back to here until there is
 						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
 						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
 
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					if (conn->sversion < 130000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_RECOVERY;
+
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
 					}
+					else if ((conn->in_recovery &&
+							  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+							 (!conn->in_recovery &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_target_connection;
 
-					conn->status = CONNECTION_CHECK_RECOVERY;
+						reject_checked_recovery_connection(conn);
+						goto keep_going;
+					}
 
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
 				/*
@@ -3932,40 +4009,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is not in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record primary host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_recovery_connection(conn);
 						goto keep_going;
 					}
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 3c17100..a964483 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1117,6 +1117,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	{
 		conn->transaction_read_only = (strcmp(value, "on") == 0);
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 0efe16f..327dd04 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -446,6 +446,7 @@ struct pg_conn
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
 	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
1.8.3.1

From cb2b1b9d07cce3cb13d9ed2276b683466d6a73fa Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Mon, 30 Sep 2019 13:23:57 +1000
Subject: [PATCH v14 2/3] Enhance libpq target_session_attrs:
 primary/prefer-standby/standby

Add new "primary" target_session_attrs option value, to support connecting to a server which is not
in recovery mode, if available from the list of hosts (otherwise the connection attempt fails).
Add new "prefer-standby" target_session_attrs option value, to support connecting to a server which
is in recovery mode, if available from the list of hosts (otherwise connect to a server which is
not in recovery mode).
Add new "standby" target_session_attrs option value, to support connecting to a server which is in
recovery mode, if available from the list of hosts (otherwise the connection attempt fails).
To determine if running in recovery mode, the server is sent the query 'SELECT pg_is_in_recovery()'.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 313 ++++++++++++++++++++++++++--------
 src/interfaces/libpq/libpq-fe.h       |  10 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 291 insertions(+), 80 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 0d3edfc..5f31fd0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1675,7 +1675,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are <literal>any</literal>,
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts are specified in the
         connection string, each host is tried in the order given until a connection
@@ -1712,6 +1713,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         in which read-only transactions are accepted by default is considered
         acceptable.
        </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        the server is not in recovery mode is considered acceptable.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable.
+       </para>
+
+       <para>
+        To determine whether the server is in recovery mode, the query
+        <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful connection;
+        if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7058f5d..0c096d1 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -350,7 +350,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1335,6 +1335,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2147,6 +2153,60 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested session type. The connection state is set to
+ * try the next host (if any).
+ * In the case of SESSION_TYPE_PREFER_READ, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a read-only host could be made after the first host scan.
+ */
+static void
+reject_checked_read_or_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -2229,6 +2289,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2268,19 +2329,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means we failed to connect to read-only servers
 				 * and should now try to connect to a read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3507,7 +3568,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 130000)
 					{
@@ -3540,55 +3603,16 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_read_or_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3597,30 +3621,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * Servers before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
+				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
 				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3755,13 +3819,119 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
+						reject_checked_read_or_write_connection(conn);
+						goto keep_going;
+					}
+
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SHOW transaction_read_only". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
+
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3771,16 +3941,14 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
 							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
+											  libpq_gettext("server is in recovery mode "
 															"\"%s:%s\"\n"),
 											  displayed_host, displayed_port);
 						else
 							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
+											  libpq_gettext("server is not in recovery mode "
 															"\"%s:%s\"\n"),
 											  displayed_host, displayed_port);
 
@@ -3788,10 +3956,10 @@ keep_going:						/* We will come back to here until there is
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3801,7 +3969,7 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-			consume_checked_write_connection:
+			consume_checked_recovery_connection:
 					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
@@ -3815,7 +3983,7 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Something went wrong with "SHOW transaction_read_only". We
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
 				 * should try next addresses.
 				 */
 				if (res)
@@ -3831,7 +3999,7 @@ keep_going:						/* We will come back to here until there is
 				if (displayed_port == NULL || displayed_port[0] == '\0')
 					displayed_port = DEF_PGPORT_STR;
 				appendPQExpBuffer(&conn->errorMessage,
-								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
 												"on server \"%s:%s\"\n"),
 								  displayed_host, displayed_port);
 
@@ -3843,7 +4011,6 @@ keep_going:						/* We will come back to here until there is
 				conn->try_next_addr = true;
 				goto keep_going;
 			}
-
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3989,7 +4156,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index aa6f22f..30b181a 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	 CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -76,8 +77,11 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
-} TargetSessionAttrsType;
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
+}			TargetSessionAttrsType;
 
 typedef enum
 {
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index eb687d8..0efe16f 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -369,7 +369,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -413,7 +413,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index ac1e11e..8fa28da 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 37;
+use Test::More tests => 41;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -141,6 +141,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1

From 74cad19872e70ffe937ad582fab30bb8f17f7a16 Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Mon, 30 Sep 2019 11:55:57 +1000
Subject: [PATCH v14 1/3] Enhance libpq target_session_attrs:
 read-write/prefer-read/read-only

Improve checking of the requested target session type, to avoid always having to do string
comparisons on target_session_attrs.
Make "transaction_read_only" a GUC_REPORT variable, to avoid having to execute a query
post-connection in order to determine whether a host is read-write (and reduce time to make the
connection).
Add new "prefer-read" target_session_attrs option value, to support connecting to a read-only
server if available from the list of hosts (otherwise connect to a read-write server).
Add new "read-only" target_session_attrs option value, to support connecting to a read-only
server if available from the list of hosts (otherwise the connection attempt fails).

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 doc/src/sgml/libpq.sgml               |  54 ++++++--
 doc/src/sgml/protocol.sgml            |   8 +-
 src/backend/utils/misc/guc.c          |   2 +-
 src/interfaces/libpq/fe-connect.c     | 239 +++++++++++++++++++++++++++++-----
 src/interfaces/libpq/fe-exec.c        |   6 +-
 src/interfaces/libpq/libpq-fe.h       |   8 ++
 src/interfaces/libpq/libpq-int.h      |  15 ++-
 src/test/recovery/t/001_stream_rep.pl |  22 +++-
 8 files changed, 299 insertions(+), 55 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c58527b..0d3edfc 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1674,18 +1674,46 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
+        The supported options for this parameter are <literal>any</literal>,
+        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts are specified in the
+        connection string, each host is tried in the order given until a connection
+        is successful.
+       </para>
+
+       <para>
         If this parameter is set to <literal>read-write</literal>, only a
         connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        is considered acceptable.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-read</literal>, a
+        connection in which read-only transactions are accepted by default
+        is preferred. If no such connections can be found, then a connection
+        in which read-write transactions are accepted will be considered.
+       </para>
+
+       <para>
+        To determine whether the server supports read-write transactions, the
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any
+        successful connection, if the server is prior to version 13; if it returns
+        <literal>on</literal>, it means the server doesn't support read-write
+        transactions.
+        If the server is version 13 or greater, the support of read-write
+        transactions is determined by the value of the
+        <varname>transaction_read_only</varname> configuration parameter that is
+        reported by the server upon successful connection.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default is considered
+        acceptable.
+       </para>
       </listitem>
-    </varlistentry>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
@@ -1993,14 +2021,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>, and
+       <varname>transaction_read_only</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 8027521..87b95bc 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELECT 1/0;
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>, and
+    <varname>transaction_read_only</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 2178e1c..c64ec03 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1543,7 +1543,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index f91f0f2..7058f5d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -350,7 +350,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1327,8 +1327,15 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_session_type = SESSION_TYPE_ANY;
+		else if (strcmp(conn->target_session_attrs, "read-write") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_WRITE;
+		else if (strcmp(conn->target_session_attrs, "prefer-read") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
+		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
+			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -2261,13 +2268,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->read_write_host_index >= 0)
+			{
+				/*
+				 * Getting here means we failed to connect to read-only servers
+				 * and should now try to connect to a read-write server again.
+				 */
+				conn->whichhost = conn->read_write_host_index;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->read_write_host_index = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3474,38 +3499,139 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a read-write, prefer-read or read-only connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+					conn->requested_session_type != SESSION_TYPE_ANY)
+				{
+					if (conn->sversion < 130000)
+					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn,
+										 "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_WRITABLE;
+
+						restoreErrorMessage(conn, &savedMessage);
+						return PGRES_POLLING_READING;
+					}
+					else if ((conn->transaction_read_only &&
+							  conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+							 (!conn->transaction_read_only &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
+					{
+						/* Not a requested type; fail this connection. */
+						const char *displayed_host;
+						const char *displayed_port;
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_target_connection;
+
+						/* Append error report to conn->errorMessage. */
+						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+							displayed_host = conn->connhost[conn->whichhost].hostaddr;
+						else
+							displayed_host = conn->connhost[conn->whichhost].host;
+						displayed_port = conn->connhost[conn->whichhost].port;
+						if (displayed_port == NULL || displayed_port[0] == '\0')
+							displayed_port = DEF_PGPORT_STR;
+
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+
+						/* Close connection politely. */
+						conn->status = CONNECTION_OK;
+						sendTerminateConn(conn);
+
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
+						/*
+						 * Try next host if any, but we don't want to consider
+						 * additional addresses for this host.
+						 */
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * Requested type is prefer-read, then record this host index
+				 * and try the other before considering it later. If requested
+				 * type of connection is read-only, ignore this connection.
+				 */
+				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
 				{
 					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
+					 * The following scenario is possible only for the
+					 * prefer-read mode for the next pass of the list of
+					 * connections as it couldn't find any servers that are
+					 * default read-only.
 					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
+					if (conn->read_write_host_index == -2)
+						goto target_accept_connection;
 
+					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
-					{
-						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
-					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+						conn->read_write_host_index == -1)
+						conn->read_write_host_index = conn->whichhost;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3604,11 +3730,35 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested mode is read-write,
+					 * ignore it. Server is read-write and requested mode is
+					 * prefer-read, record it for the first time and try to
+					 * consume in the next scan (it means no read-only server
+					 * is found in the first scan). Server is read-write and
+					 * requested mode is read-only, ignore this connection.
+					 */
+					if ((readonly_server &&
+						 conn->requested_session_type == SESSION_TYPE_READ_WRITE) ||
+						(!readonly_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						  conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-read mode for the next pass of the list of
+						 * connections as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->read_write_host_index == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
@@ -3621,16 +3771,28 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a writable "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
+						else
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("could not make a readonly "
+															"connection to server "
+															"\"%s:%s\"\n"),
+											  displayed_host, displayed_port);
 
 						/* Close connection politely. */
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
+						/* Record read-write host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+							conn->read_write_host_index == -1)
+							conn->read_write_host_index = conn->whichhost;
+
 						/*
 						 * Try next host if any, but we don't want to consider
 						 * additional addresses for this host.
@@ -3639,7 +3801,8 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3817,6 +3980,7 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
@@ -3824,6 +3988,9 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_session_type = SESSION_TYPE_ANY;
+	conn->read_write_host_index = -1;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index b3c59a0..3c17100 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1059,7 +1059,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1113,6 +1113,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 5f65db3..aa6f22f 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -73,6 +73,14 @@ typedef enum
 
 typedef enum
 {
+	SESSION_TYPE_ANY = 0,		/* Any session (default) */
+	SESSION_TYPE_READ_WRITE,	/* Read-write session */
+	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
+	SESSION_TYPE_READ_ONLY		/* Read only session */
+} TargetSessionAttrsType;
+
+typedef enum
+{
 	PGRES_POLLING_FAILED = 0,
 	PGRES_POLLING_READING,		/* These two indicate that one may	  */
 	PGRES_POLLING_WRITING,		/* use select before polling again.   */
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 64468ab..eb687d8 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -367,8 +367,12 @@ struct pg_conn
 	char	   *krbsrvname;		/* Kerberos service name */
 #endif
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: any, read-write,
+	 * prefer-read and read-only.
+	 */
 	char	   *target_session_attrs;
+	TargetSessionAttrsType requested_session_type;
 
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
@@ -403,6 +407,14 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * First read-write host index in the connection string.
+	 *
+	 * Initial value is -1, then the index of the first read-write host, -2
+	 * during the second attempt of connection to avoid recursion.
+	 */
+	int			read_write_host_index;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
@@ -433,6 +445,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 3c743d7..ac1e11e 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 32;
+use Test::More tests => 37;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -121,6 +121,26 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to standby1 in "prefer-read" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read",
+	0);
+
+# Connect to standby1 in "prefer-read" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-read", 0);
+
+# Connect to node_master in "prefer-read" mode with only master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-read", 0);
+
+# Connect to standby1 in "read-only" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"read-only", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1

From cb2b1b9d07cce3cb13d9ed2276b683466d6a73fa Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Mon, 30 Sep 2019 13:23:57 +1000
Subject: [PATCH v14 2/3] Enhance libpq target_session_attrs:
 primary/prefer-standby/standby

Add new "primary" target_session_attrs option value, to support connecting to a server which is not
in recovery mode, if available from the list of hosts (otherwise the connection attempt fails).
Add new "prefer-standby" target_session_attrs option value, to support connecting to a server which
is in recovery mode, if available from the list of hosts (otherwise connect to a server which is
not in recovery mode).
Add new "standby" target_session_attrs option value, to support connecting to a server which is in
recovery mode, if available from the list of hosts (otherwise the connection attempt fails).
To determine if running in recovery mode, the server is sent the query 'SELECT pg_is_in_recovery()'.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 doc/src/sgml/libpq.sgml               |  26 ++-
 src/interfaces/libpq/fe-connect.c     | 313 ++++++++++++++++++++++++++--------
 src/interfaces/libpq/libpq-fe.h       |  10 +-
 src/interfaces/libpq/libpq-int.h      |   4 +-
 src/test/recovery/t/001_stream_rep.pl |  18 +-
 5 files changed, 291 insertions(+), 80 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 0d3edfc..5f31fd0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1675,7 +1675,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <listitem>
        <para>
         The supported options for this parameter are <literal>any</literal>,
-        <literal>read-write</literal>, <literal>prefer-read</literal> and <literal>read-only</literal>.
+        <literal>read-write</literal>, <literal>prefer-read</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>prefer-standby</literal> and <literal>standby</literal>.
         The default value of this parameter, <literal>any</literal>, regards
         all connections as acceptable. If multiple hosts are specified in the
         connection string, each host is tried in the order given until a connection
@@ -1712,6 +1713,29 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         in which read-only transactions are accepted by default is considered
         acceptable.
        </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, only a connection in which
+        the server is not in recovery mode is considered acceptable.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable.
+       </para>
+
+       <para>
+        To determine whether the server is in recovery mode, the query
+        <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful connection;
+        if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
       </listitem>
      </varlistentry>
     </variablelist>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7058f5d..0c096d1 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -350,7 +350,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
 	/* Terminating entry --- MUST BE LAST */
@@ -1335,6 +1335,12 @@ connectOptions2(PGconn *conn)
 			conn->requested_session_type = SESSION_TYPE_PREFER_READ;
 		else if (strcmp(conn->target_session_attrs, "read-only") == 0)
 			conn->requested_session_type = SESSION_TYPE_READ_ONLY;
+		else if (strcmp(conn->target_session_attrs, "primary") == 0)
+			conn->requested_session_type = SESSION_TYPE_PRIMARY;
+		else if (strcmp(conn->target_session_attrs, "prefer-standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_PREFER_STANDBY;
+		else if (strcmp(conn->target_session_attrs, "standby") == 0)
+			conn->requested_session_type = SESSION_TYPE_STANDBY;
 		else
 		{
 			conn->status = CONNECTION_BAD;
@@ -2147,6 +2153,60 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested session type. The connection state is set to
+ * try the next host (if any).
+ * In the case of SESSION_TYPE_PREFER_READ, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a read-only host could be made after the first host scan.
+ */
+static void
+reject_checked_read_or_write_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -2229,6 +2289,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2268,19 +2329,19 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			if (conn->read_write_host_index >= 0)
+			if (conn->read_write_or_primary_host_index >= 0)
 			{
 				/*
 				 * Getting here means we failed to connect to read-only servers
 				 * and should now try to connect to a read-write server again.
 				 */
-				conn->whichhost = conn->read_write_host_index;
+				conn->whichhost = conn->read_write_or_primary_host_index;
 
 				/*
 				 * Reset the host index value to avoid recursion during the
 				 * second connection attempt.
 				 */
-				conn->read_write_host_index = -2;
+				conn->read_write_or_primary_host_index = -2;
 			}
 			else
 			{
@@ -3507,7 +3568,9 @@ keep_going:						/* We will come back to here until there is
 				 * may just skip the test in that case.
 				 */
 				if (conn->sversion >= 70400 &&
-					conn->requested_session_type != SESSION_TYPE_ANY)
+					(conn->requested_session_type == SESSION_TYPE_READ_WRITE ||
+					 conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+					 conn->requested_session_type == SESSION_TYPE_READ_ONLY))
 				{
 					if (conn->sversion < 130000)
 					{
@@ -3540,55 +3603,16 @@ keep_going:						/* We will come back to here until there is
 							  (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
 							   conn->requested_session_type == SESSION_TYPE_READ_ONLY)))
 					{
-						/* Not a requested type; fail this connection. */
-						const char *displayed_host;
-						const char *displayed_port;
-
 						/*
 						 * The following scenario is possible only for the
 						 * prefer-read mode for the next pass of the list of
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_target_connection;
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_read_or_write_connection(conn);
 						goto keep_going;
 					}
 
@@ -3597,30 +3621,70 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Requested type is prefer-read, then record this host index
-				 * and try the other before considering it later. If requested
-				 * type of connection is read-only, ignore this connection.
+				 * Servers before 9.0 don't support recovery, skip the check
+				 * when the requested type of connection is primary,
+				 * prefer-standby or standby.
+				 */
+				else if ((conn->sversion >= 90000 &&
+						  (conn->requested_session_type == SESSION_TYPE_PRIMARY ||
+						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+				{
+					/*
+					 * Save existing error messages across the PQsendQuery
+					 * attempt.  This is necessary because PQsendQuery is
+					 * going to reset conn->errorMessage, so we would lose
+					 * error messages related to previous hosts we have tried
+					 * and failed to connect to.
+					 */
+					if (!saveErrorMessage(conn, &savedMessage))
+						goto error_return;
+
+					conn->status = CONNECTION_OK;
+					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					{
+						restoreErrorMessage(conn, &savedMessage);
+						goto error_return;
+					}
+
+					conn->status = CONNECTION_CHECK_RECOVERY;
+
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				/*
+				 * Requested type is prefer-read or prefer-standby, then
+				 * record this host index and try the other before considering
+				 * it later. If requested type of connection is read-only or
+				 * standby, ignore this connection.
 				 */
+
 				if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
-					conn->requested_session_type == SESSION_TYPE_READ_ONLY)
+					conn->requested_session_type == SESSION_TYPE_READ_ONLY ||
+					conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+					conn->requested_session_type == SESSION_TYPE_STANDBY)
 				{
 					/*
 					 * The following scenario is possible only for the
-					 * prefer-read mode for the next pass of the list of
-					 * connections as it couldn't find any servers that are
-					 * default read-only.
+					 * prefer-read or prefer-standby mode for the next pass of
+					 * the list of connections as it couldn't find any servers
+					 * that are default read-only or in recovery mode.
 					 */
-					if (conn->read_write_host_index == -2)
-						goto target_accept_connection;
+					if (conn->read_write_or_primary_host_index == -2)
+						goto consume_checked_target_connection;
 
 					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
 					sendTerminateConn(conn);
 
 					/* Record read-write host index */
-					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-						conn->read_write_host_index == -1)
-						conn->read_write_host_index = conn->whichhost;
+					if (conn->requested_session_type == SESSION_TYPE_PREFER_READ ||
+						conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY)
+					{
+						if (conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
+					}
 
 					/*
 					 * Try next host if any, but we don't want to consider
@@ -3755,13 +3819,119 @@ keep_going:						/* We will come back to here until there is
 						 * connections as it couldn't find any servers that
 						 * are default read-only.
 						 */
-						if (conn->read_write_host_index == -2)
+						if (conn->read_write_or_primary_host_index == -2)
 							goto consume_checked_write_connection;
 
 						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
+						reject_checked_read_or_write_connection(conn);
+						goto keep_going;
+					}
+
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
+
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SHOW transaction_read_only". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
+
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested mode is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested mode is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server is found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+						  conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
 						/* Append error report to conn->errorMessage. */
 						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
 							displayed_host = conn->connhost[conn->whichhost].hostaddr;
@@ -3771,16 +3941,14 @@ keep_going:						/* We will come back to here until there is
 						if (displayed_port == NULL || displayed_port[0] == '\0')
 							displayed_port = DEF_PGPORT_STR;
 
-						if (conn->requested_session_type == SESSION_TYPE_READ_WRITE)
+						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
 							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a writable "
-															"connection to server "
+											  libpq_gettext("server is in recovery mode "
 															"\"%s:%s\"\n"),
 											  displayed_host, displayed_port);
 						else
 							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("could not make a readonly "
-															"connection to server "
+											  libpq_gettext("server is not in recovery mode "
 															"\"%s:%s\"\n"),
 											  displayed_host, displayed_port);
 
@@ -3788,10 +3956,10 @@ keep_going:						/* We will come back to here until there is
 						conn->status = CONNECTION_OK;
 						sendTerminateConn(conn);
 
-						/* Record read-write host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_READ &&
-							conn->read_write_host_index == -1)
-							conn->read_write_host_index = conn->whichhost;
+						/* Record primary host index */
+						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+							conn->read_write_or_primary_host_index == -1)
+							conn->read_write_or_primary_host_index = conn->whichhost;
 
 						/*
 						 * Try next host if any, but we don't want to consider
@@ -3801,7 +3969,7 @@ keep_going:						/* We will come back to here until there is
 						goto keep_going;
 					}
 
-			consume_checked_write_connection:
+			consume_checked_recovery_connection:
 					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
@@ -3815,7 +3983,7 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Something went wrong with "SHOW transaction_read_only". We
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
 				 * should try next addresses.
 				 */
 				if (res)
@@ -3831,7 +3999,7 @@ keep_going:						/* We will come back to here until there is
 				if (displayed_port == NULL || displayed_port[0] == '\0')
 					displayed_port = DEF_PGPORT_STR;
 				appendPQExpBuffer(&conn->errorMessage,
-								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
 												"on server \"%s:%s\"\n"),
 								  displayed_host, displayed_port);
 
@@ -3843,7 +4011,6 @@ keep_going:						/* We will come back to here until there is
 				conn->try_next_addr = true;
 				goto keep_going;
 			}
-
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3989,7 +4156,7 @@ makeEmptyPGconn(void)
 #endif
 
 	conn->requested_session_type = SESSION_TYPE_ANY;
-	conn->read_write_host_index = -1;
+	conn->read_write_or_primary_host_index = -1;
 
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index aa6f22f..30b181a 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	 CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
@@ -76,8 +77,11 @@ typedef enum
 	SESSION_TYPE_ANY = 0,		/* Any session (default) */
 	SESSION_TYPE_READ_WRITE,	/* Read-write session */
 	SESSION_TYPE_PREFER_READ,	/* Prefer read only session */
-	SESSION_TYPE_READ_ONLY		/* Read only session */
-} TargetSessionAttrsType;
+	SESSION_TYPE_READ_ONLY,		/* Read only session */
+	SESSION_TYPE_PRIMARY,		/* Primary server */
+	SESSION_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SESSION_TYPE_STANDBY		/* Standby server */
+}			TargetSessionAttrsType;
 
 typedef enum
 {
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index eb687d8..0efe16f 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -369,7 +369,7 @@ struct pg_conn
 
 	/*
 	 * Type of connection to make.  Possible values: any, read-write,
-	 * prefer-read and read-only.
+	 * prefer-read, read-only, primary, prefer-standby and standby.
 	 */
 	char	   *target_session_attrs;
 	TargetSessionAttrsType requested_session_type;
@@ -413,7 +413,7 @@ struct pg_conn
 	 * Initial value is -1, then the index of the first read-write host, -2
 	 * during the second attempt of connection to avoid recursion.
 	 */
-	int			read_write_host_index;
+	int			read_write_or_primary_host_index;
 
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index ac1e11e..8fa28da 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 37;
+use Test::More tests => 41;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -141,6 +141,22 @@ test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"read-only", 0);
 
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1

From 6ce04730b7fcc6fa532cbae3a2c149e3da6ae03c Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Mon, 30 Sep 2019 15:45:46 +1000
Subject: [PATCH v14 3/3] Server recovery mode handling

Add "in_recovery" as a GUC_REPORT variable, to update clients when the
server is in recovery mode. This improves the speed of client connections
to a standby server, by avoiding the need to execute a command to
determine if the server is in recovery mode.
Add new SIGUSR1 handling interrupt to support reporting of recovery mode
exit to all backends and their respective clients.
Some parts of the code is taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 doc/src/sgml/libpq.sgml              |  16 ++--
 doc/src/sgml/protocol.sgml           |   8 +-
 src/backend/access/transam/xlog.c    |   3 +
 src/backend/storage/ipc/procarray.c  |  28 +++++++
 src/backend/storage/ipc/procsignal.c |   3 +
 src/backend/storage/ipc/standby.c    |   9 +++
 src/backend/tcop/postgres.c          |  60 +++++++++++++++
 src/backend/utils/init/postinit.c    |   6 +-
 src/backend/utils/misc/check_guc     |   2 +-
 src/backend/utils/misc/guc.c         |  16 ++++
 src/include/storage/procarray.h      |   1 +
 src/include/storage/procsignal.h     |   2 +
 src/include/storage/standby.h        |   1 +
 src/include/tcop/tcopprot.h          |   2 +
 src/interfaces/libpq/fe-connect.c    | 142 +++++++++++++++++++++++------------
 src/interfaces/libpq/fe-exec.c       |   4 +
 src/interfaces/libpq/libpq-int.h     |   1 +
 17 files changed, 245 insertions(+), 59 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 5f31fd0..9f66fb8 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1732,8 +1732,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         To determine whether the server is in recovery mode, the query
-        <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful connection;
-        if it returns <literal>t</literal>, it means the server is in recovery mode.
+        <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful connection
+        if the server is prior to version 13; if it returns <literal>t</literal>, it means the server
+        is in recovery mode.
+        If the server is version 13 or greater, the recovery mode state is determined by the value of
+        the <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection.
        </para>
 
       </listitem>
@@ -2046,15 +2050,17 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
        <varname>integer_datetimes</varname>,
-       <varname>standard_conforming_strings</varname>, and
-       <varname>transaction_read_only</varname>.
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before 9.0;
-       <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by releases before 13.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 87b95bc..df3953f 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1284,15 +1284,17 @@ SELECT 1/0;
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
     <varname>integer_datetimes</varname>,
-    <varname>standard_conforming_strings</varname>, and
-    <varname>transaction_read_only</varname>.
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before 9.0;
-    <varname>transaction_read_only</varname> was not reported by releases before 13.0.)
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+    were not reported by releases before 13.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 6c69eb6..4fe506e 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7770,6 +7770,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryInProgress = false;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 8abcfdf..744475c 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2971,6 +2971,34 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 }
 
 /*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
+/*
  * ProcArraySetReplicationSlotXmin
  *
  * Install limits to future computations of the xmin horizon to prevent vacuum
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7605b2c..e4548dc 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,6 +292,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 01ddffe..b0e88ee 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -138,6 +138,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index e8d8e6f..69ce3ec 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -167,6 +167,15 @@ static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
 static StringInfoData row_description_buf;
@@ -195,6 +204,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -543,6 +553,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -2962,6 +2976,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 }
 
 /*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
+/*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
  * If an interrupt condition is pending, and it's safe to service it,
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 29c5ec7..59fb4e9 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -649,7 +649,11 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		 * This is handled by calling RecoveryInProgress and ignoring the
 		 * result.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index 416a087..a4ebcef 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_num \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index c64ec03..633bc2d 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -580,6 +580,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
+static bool in_recovery;
 
 
 /* should be static, but commands/variable.c needs to get at this */
@@ -1770,6 +1771,21 @@ static struct config_bool ConfigureNamesBool[] =
 	},
 
 	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"allow_system_table_mods", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
 			NULL,
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index da8b672..86f0c13 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
 									  int nxids, const TransactionId *xids,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 05b186a..9cf9560 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index a3f8f82..2c73f0c 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index ec21f7e..ed21a9e 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -66,6 +66,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 0c096d1..7a04618 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2207,6 +2207,58 @@ reject_checked_read_or_write_connection(PGconn *conn)
 	conn->try_next_host = true;
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested session type (for recovery). The connection state
+ * is set to try the next host (if any).
+ * In the case of SESSION_TYPE_PREFER_STANDBY, if the read-write-or-primary host-index
+ * hasn't been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+reject_checked_recovery_connection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
+		conn->read_write_or_primary_host_index == -1)
+		conn->read_write_or_primary_host_index = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -3630,27 +3682,52 @@ keep_going:						/* We will come back to here until there is
 						   conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
 						   conn->requested_session_type == SESSION_TYPE_STANDBY)))
 				{
-					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
-					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
 
-					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+					if (conn->sversion < 130000)
 					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SELECT pg_is_in_recovery()"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+
+						conn->status = CONNECTION_CHECK_RECOVERY;
+
 						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						return PGRES_POLLING_READING;
 					}
+					else if ((conn->in_recovery &&
+							  conn->requested_session_type == SESSION_TYPE_PRIMARY) ||
+							 (!conn->in_recovery &&
+							  (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY ||
+							   conn->requested_session_type == SESSION_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby mode for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->read_write_or_primary_host_index == -2)
+							goto consume_checked_target_connection;
 
-					conn->status = CONNECTION_CHECK_RECOVERY;
+						reject_checked_recovery_connection(conn);
+						goto keep_going;
+					}
 
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
 				}
 
 				/*
@@ -3932,40 +4009,7 @@ keep_going:						/* We will come back to here until there is
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						if (conn->requested_session_type == SESSION_TYPE_PRIMARY)
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-						else
-							appendPQExpBuffer(&conn->errorMessage,
-											  libpq_gettext("server is not in recovery mode "
-															"\"%s:%s\"\n"),
-											  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/* Record primary host index */
-						if (conn->requested_session_type == SESSION_TYPE_PREFER_STANDBY &&
-							conn->read_write_or_primary_host_index == -1)
-							conn->read_write_or_primary_host_index = conn->whichhost;
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						reject_checked_recovery_connection(conn);
 						goto keep_going;
 					}
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 3c17100..a964483 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1117,6 +1117,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	{
 		conn->transaction_read_only = (strcmp(value, "on") == 0);
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 0efe16f..327dd04 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -446,6 +446,7 @@ struct pg_conn
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
 	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
-- 
1.8.3.1

From 7ddf48f99db63538cdd91a49fe2c3d3c96b66e6f Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Mon, 18 May 2020 15:08:17 +1000
Subject: [PATCH v15] Enhance libpq target_session_attrs and add
 target_server_type.

Enhance the connection parameter "target_session_attrs" to support values
primary/standby/prefer-standby (using the existing "read-write" as a synonym
for "primary"). To provide closer alignment with similar functionality in the
PGJDBC driver, add a new connection parameter "target_server_type".

Add "in_recovery" as a GUC_REPORT variable, to update clients when the server
is in recovery mode. This improves the speed of client connections to a standby
server, by avoiding the need to execute a command to determine if the server is
in recovery mode.

Add new SIGUSR1 handling interrupt to support reporting of recovery mode exit
to all backends and their respective clients.

Some parts of the code are taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 contrib/postgres_fdw/expected/postgres_fdw.out |   2 +-
 doc/src/sgml/high-availability.sgml            |   5 +-
 doc/src/sgml/libpq.sgml                        | 111 +++++-
 doc/src/sgml/protocol.sgml                     |   8 +-
 src/backend/access/transam/xlog.c              |   3 +
 src/backend/storage/ipc/procarray.c            |  28 ++
 src/backend/storage/ipc/procsignal.c           |   3 +
 src/backend/storage/ipc/standby.c              |   9 +
 src/backend/tcop/postgres.c                    |  59 ++++
 src/backend/utils/init/postinit.c              |   9 +-
 src/backend/utils/misc/check_guc               |   2 +-
 src/backend/utils/misc/guc.c                   |  16 +
 src/include/storage/procarray.h                |   1 +
 src/include/storage/procsignal.h               |   2 +
 src/include/storage/standby.h                  |   1 +
 src/include/tcop/tcopprot.h                    |   2 +
 src/interfaces/libpq/fe-connect.c              | 446 ++++++++++++++++++++++---
 src/interfaces/libpq/fe-exec.c                 |   6 +-
 src/interfaces/libpq/libpq-fe.h                |   3 +-
 src/interfaces/libpq/libpq-int.h               |  48 ++-
 src/test/recovery/t/001_stream_rep.pl          | 146 +++++++-
 21 files changed, 830 insertions(+), 80 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 90db550..ba0ba6e 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8898,7 +8898,7 @@ DO $d$
     END;
 $d$;
 ERROR:  invalid option "password"
-HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
+HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, target_server_type, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
 CONTEXT:  SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
 PL/pgSQL function inline_code_block line 3 at EXECUTE
 -- If we add a password for our user mapping instead, we should get a different
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index 44cc5d2..6bc081b 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -1885,8 +1885,9 @@ if (!triggered)
    </para>
 
    <para>
-    During hot standby, the parameter <varname>transaction_read_only</varname> is always
-    true and may not be changed.  But as long as no attempt is made to modify
+    During hot standby, the parameters <varname>in_recovery</varname> and
+    <varname>transaction_read_only</varname> are always true and may not be
+    changed. But as long as no attempt is made to modify
     the database, connections during hot standby will act much like any other
     database connection.  If failover or switchover occurs, the database will
     switch to normal processing mode.  Sessions will remain connected while the
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 52631f4..8409ecc 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1811,18 +1811,89 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        If this parameter is set to <literal>read-write</literal>, only a
-        connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        The supported options for this parameter are <literal>any</literal>,
+        <literal>primary</literal>, <literal>standby</literal> and
+        <literal>prefer-standby</literal>.
+        <literal>primary</literal> may alternatively be specified as <literal>read-write</literal>.
+        <literal>standby</literal> may alternatively be specified as <literal>secondary</literal>.
+        <literal>prefer-standby</literal> may alternatively be specified as
+        <literal>prefer-secondary</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts are specified in the
+        connection string, each host is tried in the order given until a connection
+        is successful.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, then if the server is version 14
+        or greater, only a connection in which the server is not in recovery mode is considered
+        acceptable. The recovery mode state is determined by the value of the
+        <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection. Otherwise, if the server is prior to version 14, only a connection in
+        which read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions, the query
+        <literal>SHOW transaction_read_only</literal> will be sent upon any successful connection; if
+        it returns <literal>on</literal>, it means the server doesn't support read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable. If the server is prior to version 14,
+        the query <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful
+        connection; if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
       </listitem>
-    </varlistentry>
+     </varlistentry>
+
+     <varlistentry id="libpq-connect-target-server-type" xreflabel="target_server_type">
+      <term><literal>target_server_type</literal></term>
+      <listitem>
+       <para>
+        The supported options for this parameter are <literal>primary</literal>,
+        <literal>standby</literal> and <literal>prefer-standby</literal>.
+        <literal>primary</literal> may alternatively be specified as <literal>read-write</literal>.
+        <literal>standby</literal> may alternatively be specified as <literal>secondary</literal>.
+        <literal>prefer-standby</literal> may alternatively be specified as
+        <literal>prefer-secondary</literal>.
+        This parameter overrides any connection type specified by <literal>target_session_attrs</literal>.
+        If multiple hosts are specified in the connection string, each host is tried in the order given
+        until a connection is successful.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, then if the server is version 14
+        or greater, only a connection in which the server is not in recovery mode is considered
+        acceptable. The recovery mode state is determined by the value of the
+        <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection. Otherwise, if the server is prior to version 14, only a connection in
+        which read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions, the query
+        <literal>SHOW transaction_read_only</literal> will be sent upon any successful connection; if
+        it returns <literal>on</literal>, it means the server doesn't support read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable. If the server is prior to version 14,
+        the query <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful
+        connection; if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
@@ -2130,14 +2201,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>in_recovery</varname> was not reported by releases before 14.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
@@ -7237,6 +7310,16 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
       linkend="libpq-connect-target-session-attrs"/> connection parameter.
      </para>
     </listitem>
+
+    <listitem>
+     <para>
+      <indexterm>
+       <primary><envar>PGTARGETSERVERTYPE</envar></primary>
+      </indexterm>
+      <envar>PGTARGETSERVERTYPE</envar> behaves the same as the <xref
+      linkend="libpq-connect-target-server-type"/> connection parameter.
+     </para>
+    </listitem>
    </itemizedlist>
   </para>
 
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 20d1fe0..053a3ca 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;<!-- this typo is intentional -->
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>in_recovery</varname> was not reported by releases before 14.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index ca09d81..dbb3bd6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7940,6 +7940,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryState = RECOVERY_STATE_DONE;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 3c2b369..e6e63c6 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -3082,6 +3082,34 @@ TerminateOtherDBBackends(Oid databaseId)
 }
 
 /*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
+/*
  * ProcArraySetReplicationSlotXmin
  *
  * Install limits to future computations of the xmin horizon to prevent vacuum
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7b0c6ff..46a4dda 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -564,6 +564,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	if (CheckProcSignalBarrier())
 	{
 		InterruptPending = true;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index bdaf10a..2045552 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -140,6 +140,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 8958ec8..4d227db 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -162,6 +162,14 @@ static bool UseSemiNewlineNewline = false;	/* -j switch */
 static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
 
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
@@ -191,6 +199,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -539,6 +548,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -3009,6 +3022,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 }
 
 /*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
+/*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
  * If an interrupt condition is pending, and it's safe to service it,
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index f4247ea..e8f9fd0 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -646,10 +646,13 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		/*
 		 * The postmaster already started the XLOG machinery, but we need to
 		 * call InitXLOGAccess(), if the system isn't in hot-standby mode.
-		 * This is handled by calling RecoveryInProgress and ignoring the
-		 * result.
+		 * This is handled by calling RecoveryInProgress.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index 416a087..a4ebcef 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_num \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 2f3e0a7..e366b40 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -619,6 +619,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
+static bool in_recovery;
 
 
 /* should be static, but commands/variable.c needs to get at this */
@@ -1869,6 +1870,21 @@ static struct config_bool ConfigureNamesBool[] =
 	},
 
 	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"allow_system_table_mods", PGC_SUSET, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
 			NULL,
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index a5c7d0c..08b3b04 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 extern void TerminateOtherDBBackends(Oid databaseId);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 90607df..2c0a5f8 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -42,6 +42,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index cfbe426..e5d42ac 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index bd30607..d29dd1f 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -68,6 +68,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index d5da6dc..cf6e79d 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -351,9 +351,14 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
+	{"target_server_type", "PGTARGETSERVERTYPE",
+		NULL, NULL,
+		"Target-Server-Type", "", 17, /* sizeof("prefer-secondary") = 17 */
+	offsetof(struct pg_conn, target_server_type)},
+
 	/* Terminating entry --- MUST BE LAST */
 	{NULL, NULL, NULL, NULL,
 	NULL, NULL, 0}
@@ -995,6 +1000,30 @@ parse_comma_separated_list(char **startptr, bool *more)
 }
 
 /*
+ *		validateAndRecordTargetServerType
+ *
+ * Validate a given target server option value and record the requested server
+ * type. All valid target_server_type option values are also allowed in
+ * target_session_attrs (as a single option value).
+ *
+ * Returns true if OK, false if the specified option value is invalid.
+ */
+static bool
+validateAndRecordTargetServerType(const char *optionValue, TargetServerType *requestedServerType)
+{
+	if (strcmp(optionValue, "primary") == 0 || strcmp(optionValue, "read-write") == 0)
+		*requestedServerType = SERVER_TYPE_PRIMARY;
+	else if (strcmp(optionValue, "prefer-standby") == 0 || strcmp(optionValue, "prefer-secondary") == 0)
+		*requestedServerType = SERVER_TYPE_PREFER_STANDBY;
+	else if (strcmp(optionValue, "standby") == 0 || strcmp(optionValue, "secondary") == 0)
+		*requestedServerType = SERVER_TYPE_STANDBY;
+	else
+		return false;
+
+	return true;
+}
+
+/*
  *		connectOptions2
  *
  * Compute derived connection options after absorbing all user-supplied info.
@@ -1387,8 +1416,9 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_server_type = SERVER_TYPE_ANY;
+		else if (!validateAndRecordTargetServerType(conn->target_session_attrs, &conn->requested_server_type))
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -1399,6 +1429,23 @@ connectOptions2(PGconn *conn)
 	}
 
 	/*
+	 * Validate target_server_type option.
+	 * If a target_server_type is specified, it overrides any target server
+	 * type specified in target_session_attrs.
+	 */
+	if (conn->target_server_type)
+	{
+		if (!validateAndRecordTargetServerType(conn->target_server_type, &conn->requested_server_type))
+		{
+			conn->status = CONNECTION_BAD;
+			printfPQExpBuffer(&conn->errorMessage,
+							  libpq_gettext("invalid target_server_type value: \"%s\"\n"),
+							  conn->target_server_type);
+			return false;
+		}
+	}
+
+	/*
 	 * Only if we get this far is it appropriate to try to connect. (We need a
 	 * state flag, rather than just the boolean result of this function, in
 	 * case someone tries to PQreset() the PGconn.)
@@ -2223,6 +2270,110 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type. The connection state is set to
+ * try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedReadOrWriteConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_rw_host == -1)
+		conn->which_rw_host = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type (for recovery). The connection state
+ * is set to try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedRecoveryConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_rw_host == -1)
+		conn->which_rw_host = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -2305,6 +2456,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2341,12 +2493,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->which_rw_host >= 0)
+			{
+				/*
+				 * Getting here means we failed to connect to read-only servers
+				 * and should now try to re-connect to a previously-connected-to
+				 * read-write server, whose host index is recorded in which_rw_host.
+				 */
+				conn->whichhost = conn->which_rw_host;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->which_rw_host = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
+		else
 		conn->whichhost++;
 
 		/* Drop any address info for previous host */
@@ -3556,38 +3727,102 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a primary (not-in-recovery / read-write) connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
-				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+				if ((conn->sversion >= 70400 &&
+					  (conn->requested_server_type == SERVER_TYPE_PRIMARY ||
+					   conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+					   conn->requested_server_type == SERVER_TYPE_STANDBY)))
+				{
+					if (conn->sversion < 140000)
+					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
+						restoreErrorMessage(conn, &savedMessage);
+						return PGRES_POLLING_READING;
+					}
+					else if ((conn->in_recovery &&
+						  conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						 (!conn->in_recovery &&
+						  (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						   conn->requested_server_type == SERVER_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list
+						 * of connections, as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->which_rw_host == -2)
+							goto consume_checked_target_connection;
+
+						rejectCheckedRecoveryConnection(conn);
+						goto keep_going;
+					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * If the Requested type of connection is prefer-standby, then record
+				 * this host index and try other specified hosts before considering it later.
+				 * If the requested type of connection is standby, ignore this connection.
+				 */
+
+				if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+					conn->requested_server_type == SERVER_TYPE_STANDBY)
 				{
 					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
+					 * The following scenario is possible only for the
+					 * prefer-standby mode for the next pass of the list
+					 * of connections, as it couldn't find any servers that
+					 * are in recovery.
 					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
+					if (conn->which_rw_host == -2)
+						goto consume_checked_target_connection;
 
+					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY)
 					{
-						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						if (conn->which_rw_host == -1)
+							conn->which_rw_host = conn->whichhost;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3686,42 +3921,149 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested server type is primary,
+					 * ignore it. Server is read-write and requested type is
+					 * prefer-standby, record it for the first time and try to
+					 * consume in the next scan (it means no standby server
+					 * was found in the first scan). Server is read-write and
+					 * requested type is standby, ignore this connection.
+					 */
+					if ((readonly_server &&
+						 conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						(!readonly_server &&
+						 (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						  conn->requested_server_type == SERVER_TYPE_STANDBY)))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list of
+						 * connections, as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->which_rw_host == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
+						rejectCheckedReadOrWriteConnection(conn);
+						goto keep_going;
+					}
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
 
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SHOW transaction_read_only". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
+
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
 
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested type is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested type is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server was found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						  conn->requested_server_type == SERVER_TYPE_STANDBY)))
+					{
 						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list
+						 * of connections, as it couldn't find any servers that
+						 * are in recovery.
 						 */
-						conn->try_next_host = true;
+						if (conn->which_rw_host == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						rejectCheckedRecoveryConnection(conn);
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3734,7 +4076,7 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Something went wrong with "SHOW transaction_read_only". We
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
 				 * should try next addresses.
 				 */
 				if (res)
@@ -3750,7 +4092,7 @@ keep_going:						/* We will come back to here until there is
 				if (displayed_port == NULL || displayed_port[0] == '\0')
 					displayed_port = DEF_PGPORT_STR;
 				appendPQExpBuffer(&conn->errorMessage,
-								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
 												"on server \"%s:%s\"\n"),
 								  displayed_host, displayed_port);
 
@@ -3762,7 +4104,6 @@ keep_going:						/* We will come back to here until there is
 				conn->try_next_addr = true;
 				goto keep_going;
 			}
-
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3906,6 +4247,9 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_server_type = SERVER_TYPE_ANY;
+	conn->which_rw_host = -1;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index eea0237..be73aa7 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1058,7 +1058,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1112,6 +1112,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 3b6a9fb..9c59feb 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 1de91ae..8033fc0 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -317,6 +317,15 @@ typedef struct pg_conn_host
 								 * found in password file. */
 } pg_conn_host;
 
+/* Target server type to connect to */
+typedef enum
+{
+	SERVER_TYPE_ANY = 0,           /* Any server (default) */
+	SERVER_TYPE_PRIMARY,           /* Primary server */
+	SERVER_TYPE_PREFER_STANDBY,    /* Prefer Standby server */
+	SERVER_TYPE_STANDBY            /* Standby server */
+} TargetServerType;
+
 /*
  * PGconn stores all the state data associated with a single connection
  * to a backend.
@@ -370,9 +379,33 @@ struct pg_conn
 	char	   *ssl_min_protocol_version;	/* minimum TLS protocol version */
 	char	   *ssl_max_protocol_version;	/* maximum TLS protocol version */
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values:
+	 * 	"any"
+	 * 	"primary" (or "read-write")
+	 * 	"prefer-standby" (or "prefer-secondary")
+	 * 	"standby" (or "secondary").
+	 */
 	char	   *target_session_attrs;
 
+	/*
+	 * Type of server to connect to. Possible values:
+	 * 	"primary" (or "read-write")
+	 * 	"prefer-standby" (or "prefer-secondary")
+	 * 	"standby" (or "secondary").
+	 * This overrides any connection type specified by target_session_attrs.
+	 * This option is almost a synonym for the target_session_attrs option, except
+	 * its purpose is to closely reflect the similar PGJDBC targetServerType option.
+	 * Note also that this option only accepts single option values, whereas in
+	 * future, target_session_attrs may accept multiple session attribute values.
+	 */
+	char	   *target_server_type;
+
+	/*
+	 * The requested server type, derived from target_session_attrs / target_server_type.
+	 */
+	TargetServerType requested_server_type;
+
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
 
@@ -406,6 +439,17 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * Index of the first read-write host encountered (if any) in the connection string.
+	 *
+	 * The initial value is -1, indicating that no read-write host has yet been found.
+	 * It is then set to the index of the first read-write host, if one is found in the
+	 * connection string during processing. If a second connection attempt is later made
+	 * to that read-write host, which_rw_host is then set to -2 to avoid recursion during
+	 * processing (and whichhost is set to the read-write host index).
+	 */
+	int			which_rw_host;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
@@ -436,6 +480,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
@@ -540,7 +585,6 @@ struct pg_cancel
 	int			be_key;			/* key of backend --- needed for cancels */
 };
 
-
 /* String descriptions of the ExecStatusTypes.
  * direct use of this array is deprecated; call PQresStatus() instead.
  */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 0c316c1..1dc7ba0 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 35;
+use Test::More tests => 61;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -121,6 +121,150 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to master in "primary" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_master,
+	"primary", 0);
+
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to master in "prefer-secondary" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-ssecondary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "standby" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "secondary" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"secondary", 0);
+
+# Tests for connection parameter target_server_type
+note "testing connection parameter \"target_server_type\"";
+
+# Routine designed to run tests on the connection parameter
+# target_server_type with multiple nodes.
+sub test_target_server_type
+{
+	my $node1       = shift;
+	my $node2       = shift;
+	my $target_node = shift;
+	my $mode        = shift;
+	my $status      = shift;
+
+	my $node1_host = $node1->host;
+	my $node1_port = $node1->port;
+	my $node1_name = $node1->name;
+	my $node2_host = $node2->host;
+	my $node2_port = $node2->port;
+	my $node2_name = $node2->name;
+
+	my $target_name = $target_node->name;
+
+	# Build connection string for connection attempt.
+	my $connstr = "host=$node1_host,$node2_host ";
+	$connstr .= "port=$node1_port,$node2_port ";
+	$connstr .= "target_server_type=$mode";
+
+	# The client used for the connection does not matter, only the backend
+	# point does.
+	my ($ret, $stdout, $stderr) =
+	  $node1->psql('postgres', 'SHOW port;',
+		extra_params => [ '-d', $connstr ]);
+	is( $status == $ret && $stdout eq $target_node->port,
+		1,
+		"connect to node $target_name if mode \"$mode\" and $node1_name,$node2_name listed"
+	);
+
+	return;
+}
+
+# Connect to master in "read-write" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_master,
+	"read-write", 0);
+
+# Connect to master in "read-write" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_master,
+	"read-write", 0);
+
+# Connect to master in "primary" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_master,
+	"primary", 0);
+
+# Connect to master in "primary" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_server_type($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to master in "prefer-secondary" mode with master,master list.
+test_target_server_type($node_master, $node_master, $node_master,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "standby" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "secondary" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"secondary", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1

From 6800792d3c6ff3853b47ed33e54f63de18f4b657 Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Fri, 3 Jul 2020 14:44:27 +1000
Subject: [PATCH v16] Enhance libpq target_session_attrs and add
 target_server_type.

Enhance the connection parameter "target_session_attrs" to support values
primary/standby/prefer-standby (using the existing "read-write" as a synonym
for "primary"). To provide closer alignment with similar functionality in the
PGJDBC driver, add a new connection parameter "target_server_type".

Add "in_recovery" as a GUC_REPORT variable, to update clients when the server
is in recovery mode. This improves the speed of client connections to a standby
server, by avoiding the need to execute a command to determine if the server is
in recovery mode.

Add new SIGUSR1 handling interrupt to support reporting of recovery mode exit
to all backends and their respective clients.

Some parts of the code are taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 contrib/postgres_fdw/expected/postgres_fdw.out |   2 +-
 doc/src/sgml/high-availability.sgml            |   5 +-
 doc/src/sgml/libpq.sgml                        | 111 +++++-
 doc/src/sgml/protocol.sgml                     |   8 +-
 src/backend/access/transam/xlog.c              |   3 +
 src/backend/storage/ipc/procarray.c            |  28 ++
 src/backend/storage/ipc/procsignal.c           |   3 +
 src/backend/storage/ipc/standby.c              |   9 +
 src/backend/tcop/postgres.c                    |  59 ++++
 src/backend/utils/init/postinit.c              |   9 +-
 src/backend/utils/misc/check_guc               |   2 +-
 src/backend/utils/misc/guc.c                   |  16 +
 src/include/storage/procarray.h                |   1 +
 src/include/storage/procsignal.h               |   2 +
 src/include/storage/standby.h                  |   1 +
 src/include/tcop/tcopprot.h                    |   2 +
 src/interfaces/libpq/fe-connect.c              | 446 ++++++++++++++++++++++---
 src/interfaces/libpq/fe-exec.c                 |   6 +-
 src/interfaces/libpq/libpq-fe.h                |   3 +-
 src/interfaces/libpq/libpq-int.h               |  48 ++-
 src/test/recovery/t/001_stream_rep.pl          | 146 +++++++-
 21 files changed, 830 insertions(+), 80 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 82fc129..13d1c72 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8898,7 +8898,7 @@ DO $d$
     END;
 $d$;
 ERROR:  invalid option "password"
-HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
+HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, target_server_type, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
 CONTEXT:  SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
 PL/pgSQL function inline_code_block line 3 at EXECUTE
 -- If we add a password for our user mapping instead, we should get a different
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index 65c3fc6..f81a7d6 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -1887,8 +1887,9 @@ if (!triggered)
    </para>
 
    <para>
-    During hot standby, the parameter <varname>transaction_read_only</varname> is always
-    true and may not be changed.  But as long as no attempt is made to modify
+    During hot standby, the parameters <varname>in_recovery</varname> and
+    <varname>transaction_read_only</varname> are always true and may not be
+    changed. But as long as no attempt is made to modify
     the database, connections during hot standby will act much like any other
     database connection.  If failover or switchover occurs, the database will
     switch to normal processing mode.  Sessions will remain connected while the
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index ea1909c..f8d0a6d 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1811,18 +1811,89 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        If this parameter is set to <literal>read-write</literal>, only a
-        connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        The supported options for this parameter are <literal>any</literal>,
+        <literal>primary</literal>, <literal>standby</literal> and
+        <literal>prefer-standby</literal>.
+        <literal>primary</literal> may alternatively be specified as <literal>read-write</literal>.
+        <literal>standby</literal> may alternatively be specified as <literal>secondary</literal>.
+        <literal>prefer-standby</literal> may alternatively be specified as
+        <literal>prefer-secondary</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts are specified in the
+        connection string, each host is tried in the order given until a connection
+        is successful.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, then if the server is version 14
+        or greater, only a connection in which the server is not in recovery mode is considered
+        acceptable. The recovery mode state is determined by the value of the
+        <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection. Otherwise, if the server is prior to version 14, only a connection in
+        which read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions, the query
+        <literal>SHOW transaction_read_only</literal> will be sent upon any successful connection; if
+        it returns <literal>on</literal>, it means the server doesn't support read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable. If the server is prior to version 14,
+        the query <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful
+        connection; if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
       </listitem>
-    </varlistentry>
+     </varlistentry>
+
+     <varlistentry id="libpq-connect-target-server-type" xreflabel="target_server_type">
+      <term><literal>target_server_type</literal></term>
+      <listitem>
+       <para>
+        The supported options for this parameter are <literal>primary</literal>,
+        <literal>standby</literal> and <literal>prefer-standby</literal>.
+        <literal>primary</literal> may alternatively be specified as <literal>read-write</literal>.
+        <literal>standby</literal> may alternatively be specified as <literal>secondary</literal>.
+        <literal>prefer-standby</literal> may alternatively be specified as
+        <literal>prefer-secondary</literal>.
+        This parameter overrides any connection type specified by <literal>target_session_attrs</literal>.
+        If multiple hosts are specified in the connection string, each host is tried in the order given
+        until a connection is successful.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, then if the server is version 14
+        or greater, only a connection in which the server is not in recovery mode is considered
+        acceptable. The recovery mode state is determined by the value of the
+        <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection. Otherwise, if the server is prior to version 14, only a connection in
+        which read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions, the query
+        <literal>SHOW transaction_read_only</literal> will be sent upon any successful connection; if
+        it returns <literal>on</literal>, it means the server doesn't support read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable. If the server is prior to version 14,
+        the query <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful
+        connection; if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
@@ -2130,14 +2201,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>in_recovery</varname> was not reported by releases before 14.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
@@ -7237,6 +7310,16 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
       linkend="libpq-connect-target-session-attrs"/> connection parameter.
      </para>
     </listitem>
+
+    <listitem>
+     <para>
+      <indexterm>
+       <primary><envar>PGTARGETSERVERTYPE</envar></primary>
+      </indexterm>
+      <envar>PGTARGETSERVERTYPE</envar> behaves the same as the <xref
+      linkend="libpq-connect-target-server-type"/> connection parameter.
+     </para>
+    </listitem>
    </itemizedlist>
   </para>
 
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 20d1fe0..053a3ca 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;<!-- this typo is intentional -->
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>in_recovery</varname> was not reported by releases before 14.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index fd93bcf..49b8758 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7943,6 +7943,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryState = RECOVERY_STATE_DONE;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 3c2b369..e6e63c6 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -3082,6 +3082,34 @@ TerminateOtherDBBackends(Oid databaseId)
 }
 
 /*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
+/*
  * ProcArraySetReplicationSlotXmin
  *
  * Install limits to future computations of the xmin horizon to prevent vacuum
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 4fa385b..957df0d 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -585,6 +585,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 9e0d5ec..f2790b6 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -140,6 +140,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index c9424f1..6e0481e 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -162,6 +162,14 @@ static bool UseSemiNewlineNewline = false;	/* -j switch */
 static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
 
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
@@ -191,6 +199,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -539,6 +548,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -3009,6 +3022,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 }
 
 /*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
+/*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
  * If an interrupt condition is pending, and it's safe to service it,
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index f4247ea..e8f9fd0 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -646,10 +646,13 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		/*
 		 * The postmaster already started the XLOG machinery, but we need to
 		 * call InitXLOGAccess(), if the system isn't in hot-standby mode.
-		 * This is handled by calling RecoveryInProgress and ignoring the
-		 * result.
+		 * This is handled by calling RecoveryInProgress.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index 416a087..a4ebcef 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_num \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 75fc6f1..49c8fa8 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -610,6 +610,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
+static bool in_recovery;
 
 
 /* should be static, but commands/variable.c needs to get at this */
@@ -1850,6 +1851,21 @@ static struct config_bool ConfigureNamesBool[] =
 	},
 
 	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"allow_system_table_mods", PGC_SUSET, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
 			NULL,
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index a5c7d0c..08b3b04 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 extern void TerminateOtherDBBackends(Oid databaseId);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 5cb3969..6c243d4 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -43,6 +43,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index cfbe426..e5d42ac 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index bd30607..d29dd1f 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -68,6 +68,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 27c9bb4..1d30ec8 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -351,9 +351,14 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
+	{"target_server_type", "PGTARGETSERVERTYPE",
+		NULL, NULL,
+		"Target-Server-Type", "", 17, /* sizeof("prefer-secondary") = 17 */
+	offsetof(struct pg_conn, target_server_type)},
+
 	/* Terminating entry --- MUST BE LAST */
 	{NULL, NULL, NULL, NULL,
 	NULL, NULL, 0}
@@ -995,6 +1000,30 @@ parse_comma_separated_list(char **startptr, bool *more)
 }
 
 /*
+ *		validateAndRecordTargetServerType
+ *
+ * Validate a given target server option value and record the requested server
+ * type. All valid target_server_type option values are also allowed in
+ * target_session_attrs (as a single option value).
+ *
+ * Returns true if OK, false if the specified option value is invalid.
+ */
+static bool
+validateAndRecordTargetServerType(const char *optionValue, TargetServerType *requestedServerType)
+{
+	if (strcmp(optionValue, "primary") == 0 || strcmp(optionValue, "read-write") == 0)
+		*requestedServerType = SERVER_TYPE_PRIMARY;
+	else if (strcmp(optionValue, "prefer-standby") == 0 || strcmp(optionValue, "prefer-secondary") == 0)
+		*requestedServerType = SERVER_TYPE_PREFER_STANDBY;
+	else if (strcmp(optionValue, "standby") == 0 || strcmp(optionValue, "secondary") == 0)
+		*requestedServerType = SERVER_TYPE_STANDBY;
+	else
+		return false;
+
+	return true;
+}
+
+/*
  *		connectOptions2
  *
  * Compute derived connection options after absorbing all user-supplied info.
@@ -1390,8 +1419,9 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_server_type = SERVER_TYPE_ANY;
+		else if (!validateAndRecordTargetServerType(conn->target_session_attrs, &conn->requested_server_type))
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -1403,6 +1433,23 @@ connectOptions2(PGconn *conn)
 	}
 
 	/*
+	 * Validate target_server_type option.
+	 * If a target_server_type is specified, it overrides any target server
+	 * type specified in target_session_attrs.
+	 */
+	if (conn->target_server_type)
+	{
+		if (!validateAndRecordTargetServerType(conn->target_server_type, &conn->requested_server_type))
+		{
+			conn->status = CONNECTION_BAD;
+			printfPQExpBuffer(&conn->errorMessage,
+							  libpq_gettext("invalid target_server_type value: \"%s\"\n"),
+							  conn->target_server_type);
+			return false;
+		}
+	}
+
+	/*
 	 * Only if we get this far is it appropriate to try to connect. (We need a
 	 * state flag, rather than just the boolean result of this function, in
 	 * case someone tries to PQreset() the PGconn.)
@@ -2227,6 +2274,110 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type. The connection state is set to
+ * try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedReadOrWriteConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_rw_host == -1)
+		conn->which_rw_host = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type (for recovery). The connection state
+ * is set to try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedRecoveryConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_rw_host == -1)
+		conn->which_rw_host = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -2309,6 +2460,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2345,12 +2497,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->which_rw_host >= 0)
+			{
+				/*
+				 * Getting here means we failed to connect to read-only servers
+				 * and should now try to re-connect to a previously-connected-to
+				 * read-write server, whose host index is recorded in which_rw_host.
+				 */
+				conn->whichhost = conn->which_rw_host;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->which_rw_host = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
+		else
 		conn->whichhost++;
 
 		/* Drop any address info for previous host */
@@ -3560,38 +3731,102 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a primary (not-in-recovery / read-write) connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
-				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+				if ((conn->sversion >= 70400 &&
+					  (conn->requested_server_type == SERVER_TYPE_PRIMARY ||
+					   conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+					   conn->requested_server_type == SERVER_TYPE_STANDBY)))
+				{
+					if (conn->sversion < 140000)
+					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
+						restoreErrorMessage(conn, &savedMessage);
+						return PGRES_POLLING_READING;
+					}
+					else if ((conn->in_recovery &&
+						  conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						 (!conn->in_recovery &&
+						  (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						   conn->requested_server_type == SERVER_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list
+						 * of connections, as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->which_rw_host == -2)
+							goto consume_checked_target_connection;
+
+						rejectCheckedRecoveryConnection(conn);
+						goto keep_going;
+					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * If the Requested type of connection is prefer-standby, then record
+				 * this host index and try other specified hosts before considering it later.
+				 * If the requested type of connection is standby, ignore this connection.
+				 */
+
+				if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+					conn->requested_server_type == SERVER_TYPE_STANDBY)
 				{
 					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
+					 * The following scenario is possible only for the
+					 * prefer-standby mode for the next pass of the list
+					 * of connections, as it couldn't find any servers that
+					 * are in recovery.
 					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
+					if (conn->which_rw_host == -2)
+						goto consume_checked_target_connection;
 
+					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY)
 					{
-						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						if (conn->which_rw_host == -1)
+							conn->which_rw_host = conn->whichhost;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3690,42 +3925,149 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested server type is primary,
+					 * ignore it. Server is read-write and requested type is
+					 * prefer-standby, record it for the first time and try to
+					 * consume in the next scan (it means no standby server
+					 * was found in the first scan). Server is read-write and
+					 * requested type is standby, ignore this connection.
+					 */
+					if ((readonly_server &&
+						 conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						(!readonly_server &&
+						 (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						  conn->requested_server_type == SERVER_TYPE_STANDBY)))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list of
+						 * connections, as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->which_rw_host == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
+						rejectCheckedReadOrWriteConnection(conn);
+						goto keep_going;
+					}
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
 
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SHOW transaction_read_only". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
+
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
 
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
+
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested type is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested type is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server was found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						  conn->requested_server_type == SERVER_TYPE_STANDBY)))
+					{
 						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list
+						 * of connections, as it couldn't find any servers that
+						 * are in recovery.
 						 */
-						conn->try_next_host = true;
+						if (conn->which_rw_host == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						rejectCheckedRecoveryConnection(conn);
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3738,7 +4080,7 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Something went wrong with "SHOW transaction_read_only". We
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
 				 * should try next addresses.
 				 */
 				if (res)
@@ -3754,7 +4096,7 @@ keep_going:						/* We will come back to here until there is
 				if (displayed_port == NULL || displayed_port[0] == '\0')
 					displayed_port = DEF_PGPORT_STR;
 				appendPQExpBuffer(&conn->errorMessage,
-								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
 												"on server \"%s:%s\"\n"),
 								  displayed_host, displayed_port);
 
@@ -3766,7 +4108,6 @@ keep_going:						/* We will come back to here until there is
 				conn->try_next_addr = true;
 				goto keep_going;
 			}
-
 		default:
 			appendPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid connection state %d, "
@@ -3910,6 +4251,9 @@ makeEmptyPGconn(void)
 	conn->try_gss = true;
 #endif
 
+	conn->requested_server_type = SERVER_TYPE_ANY;
+	conn->which_rw_host = -1;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index eea0237..be73aa7 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1058,7 +1058,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1112,6 +1112,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 3b6a9fb..9c59feb 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 1de91ae..8033fc0 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -317,6 +317,15 @@ typedef struct pg_conn_host
 								 * found in password file. */
 } pg_conn_host;
 
+/* Target server type to connect to */
+typedef enum
+{
+	SERVER_TYPE_ANY = 0,           /* Any server (default) */
+	SERVER_TYPE_PRIMARY,           /* Primary server */
+	SERVER_TYPE_PREFER_STANDBY,    /* Prefer Standby server */
+	SERVER_TYPE_STANDBY            /* Standby server */
+} TargetServerType;
+
 /*
  * PGconn stores all the state data associated with a single connection
  * to a backend.
@@ -370,9 +379,33 @@ struct pg_conn
 	char	   *ssl_min_protocol_version;	/* minimum TLS protocol version */
 	char	   *ssl_max_protocol_version;	/* maximum TLS protocol version */
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values:
+	 * 	"any"
+	 * 	"primary" (or "read-write")
+	 * 	"prefer-standby" (or "prefer-secondary")
+	 * 	"standby" (or "secondary").
+	 */
 	char	   *target_session_attrs;
 
+	/*
+	 * Type of server to connect to. Possible values:
+	 * 	"primary" (or "read-write")
+	 * 	"prefer-standby" (or "prefer-secondary")
+	 * 	"standby" (or "secondary").
+	 * This overrides any connection type specified by target_session_attrs.
+	 * This option is almost a synonym for the target_session_attrs option, except
+	 * its purpose is to closely reflect the similar PGJDBC targetServerType option.
+	 * Note also that this option only accepts single option values, whereas in
+	 * future, target_session_attrs may accept multiple session attribute values.
+	 */
+	char	   *target_server_type;
+
+	/*
+	 * The requested server type, derived from target_session_attrs / target_server_type.
+	 */
+	TargetServerType requested_server_type;
+
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
 
@@ -406,6 +439,17 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * Index of the first read-write host encountered (if any) in the connection string.
+	 *
+	 * The initial value is -1, indicating that no read-write host has yet been found.
+	 * It is then set to the index of the first read-write host, if one is found in the
+	 * connection string during processing. If a second connection attempt is later made
+	 * to that read-write host, which_rw_host is then set to -2 to avoid recursion during
+	 * processing (and whichhost is set to the read-write host index).
+	 */
+	int			which_rw_host;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
@@ -436,6 +480,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
@@ -540,7 +585,6 @@ struct pg_cancel
 	int			be_key;			/* key of backend --- needed for cancels */
 };
 
-
 /* String descriptions of the ExecStatusTypes.
  * direct use of this array is deprecated; call PQresStatus() instead.
  */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 778f11b..761d34d 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 36;
+use Test::More tests => 62;
 
 # Initialize master node
 my $node_master = get_new_node('master');
@@ -121,6 +121,150 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any",
 test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
 	"any", 0);
 
+# Connect to master in "primary" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_master,
+	"primary", 0);
+
+# Connect to master in "primary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to master in "prefer-secondary" mode with master,master list.
+test_target_session_attrs($node_master, $node_master, $node_master,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-ssecondary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "standby" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "secondary" mode with master,standby1 list.
+test_target_session_attrs($node_master, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,master list.
+test_target_session_attrs($node_standby_1, $node_master, $node_standby_1,
+	"secondary", 0);
+
+# Tests for connection parameter target_server_type
+note "testing connection parameter \"target_server_type\"";
+
+# Routine designed to run tests on the connection parameter
+# target_server_type with multiple nodes.
+sub test_target_server_type
+{
+	my $node1       = shift;
+	my $node2       = shift;
+	my $target_node = shift;
+	my $mode        = shift;
+	my $status      = shift;
+
+	my $node1_host = $node1->host;
+	my $node1_port = $node1->port;
+	my $node1_name = $node1->name;
+	my $node2_host = $node2->host;
+	my $node2_port = $node2->port;
+	my $node2_name = $node2->name;
+
+	my $target_name = $target_node->name;
+
+	# Build connection string for connection attempt.
+	my $connstr = "host=$node1_host,$node2_host ";
+	$connstr .= "port=$node1_port,$node2_port ";
+	$connstr .= "target_server_type=$mode";
+
+	# The client used for the connection does not matter, only the backend
+	# point does.
+	my ($ret, $stdout, $stderr) =
+	  $node1->psql('postgres', 'SHOW port;',
+		extra_params => [ '-d', $connstr ]);
+	is( $status == $ret && $stdout eq $target_node->port,
+		1,
+		"connect to node $target_name if mode \"$mode\" and $node1_name,$node2_name listed"
+	);
+
+	return;
+}
+
+# Connect to master in "read-write" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_master,
+	"read-write", 0);
+
+# Connect to master in "read-write" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_master,
+	"read-write", 0);
+
+# Connect to master in "primary" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_master,
+	"primary", 0);
+
+# Connect to master in "primary" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_master,
+	"primary", 0);
+
+# Connect to master in "prefer-standby" mode with master,master list.
+test_target_server_type($node_master, $node_master, $node_master,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to master in "prefer-secondary" mode with master,master list.
+test_target_server_type($node_master, $node_master, $node_master,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "standby" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "standby" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "secondary" mode with master,standby1 list.
+test_target_server_type($node_master, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,master list.
+test_target_server_type($node_standby_1, $node_master, $node_standby_1,
+	"secondary", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1

From 9f957fa1556725f7a86e0a4f61b52b3f1bbfa571 Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Sun, 19 Jul 2020 21:45:15 +1000
Subject: [PATCH v17] Enhance libpq target_session_attrs and add
 target_server_type.

Enhance the connection parameter "target_session_attrs" to support values
primary/standby/prefer-standby (using the existing "read-write" as a synonym
for "primary"). To provide closer alignment with similar functionality in the
PGJDBC driver, add a new connection parameter "target_server_type".

Add "in_recovery" as a GUC_REPORT variable, to update clients when the server
is in recovery mode. This improves the speed of client connections to a standby
server, by avoiding the need to execute a command to determine if the server is
in recovery mode.

Add new SIGUSR1 handling interrupt to support reporting of recovery mode exit
to all backends and their respective clients.

Some parts of the code are taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 contrib/postgres_fdw/expected/postgres_fdw.out |   2 +-
 doc/src/sgml/high-availability.sgml            |   5 +-
 doc/src/sgml/libpq.sgml                        | 111 +++++-
 doc/src/sgml/protocol.sgml                     |   8 +-
 src/backend/access/transam/xlog.c              |   3 +
 src/backend/storage/ipc/procarray.c            |  28 ++
 src/backend/storage/ipc/procsignal.c           |   3 +
 src/backend/storage/ipc/standby.c              |   9 +
 src/backend/tcop/postgres.c                    |  59 ++++
 src/backend/utils/init/postinit.c              |   9 +-
 src/backend/utils/misc/check_guc               |   2 +-
 src/backend/utils/misc/guc.c                   |  16 +
 src/include/storage/procarray.h                |   1 +
 src/include/storage/procsignal.h               |   2 +
 src/include/storage/standby.h                  |   1 +
 src/include/tcop/tcopprot.h                    |   2 +
 src/interfaces/libpq/fe-connect.c              | 445 ++++++++++++++++++++++---
 src/interfaces/libpq/fe-exec.c                 |   6 +-
 src/interfaces/libpq/libpq-fe.h                |   3 +-
 src/interfaces/libpq/libpq-int.h               |  48 ++-
 src/test/recovery/t/001_stream_rep.pl          | 146 +++++++-
 21 files changed, 830 insertions(+), 79 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 90db550..ba0ba6e 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8898,7 +8898,7 @@ DO $d$
     END;
 $d$;
 ERROR:  invalid option "password"
-HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
+HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, target_server_type, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
 CONTEXT:  SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
 PL/pgSQL function inline_code_block line 3 at EXECUTE
 -- If we add a password for our user mapping instead, we should get a different
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index 6a9184f..e2b8cfa 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -1886,8 +1886,9 @@ if (!triggered)
    </para>
 
    <para>
-    During hot standby, the parameter <varname>transaction_read_only</varname> is always
-    true and may not be changed.  But as long as no attempt is made to modify
+    During hot standby, the parameters <varname>in_recovery</varname> and
+    <varname>transaction_read_only</varname> are always true and may not be
+    changed. But as long as no attempt is made to modify
     the database, connections during hot standby will act much like any other
     database connection.  If failover or switchover occurs, the database will
     switch to normal processing mode.  Sessions will remain connected while the
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index f7b765f..26673c9 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1811,18 +1811,89 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        If this parameter is set to <literal>read-write</literal>, only a
-        connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        The supported options for this parameter are <literal>any</literal>,
+        <literal>primary</literal>, <literal>standby</literal> and
+        <literal>prefer-standby</literal>.
+        <literal>primary</literal> may alternatively be specified as <literal>read-write</literal>.
+        <literal>standby</literal> may alternatively be specified as <literal>secondary</literal>.
+        <literal>prefer-standby</literal> may alternatively be specified as
+        <literal>prefer-secondary</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts are specified in the
+        connection string, each host is tried in the order given until a connection
+        is successful.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, then if the server is version 14
+        or greater, only a connection in which the server is not in recovery mode is considered
+        acceptable. The recovery mode state is determined by the value of the
+        <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection. Otherwise, if the server is prior to version 14, only a connection in
+        which read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions, the query
+        <literal>SHOW transaction_read_only</literal> will be sent upon any successful connection; if
+        it returns <literal>on</literal>, it means the server doesn't support read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable. If the server is prior to version 14,
+        the query <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful
+        connection; if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
       </listitem>
-    </varlistentry>
+     </varlistentry>
+
+     <varlistentry id="libpq-connect-target-server-type" xreflabel="target_server_type">
+      <term><literal>target_server_type</literal></term>
+      <listitem>
+       <para>
+        The supported options for this parameter are <literal>primary</literal>,
+        <literal>standby</literal> and <literal>prefer-standby</literal>.
+        <literal>primary</literal> may alternatively be specified as <literal>read-write</literal>.
+        <literal>standby</literal> may alternatively be specified as <literal>secondary</literal>.
+        <literal>prefer-standby</literal> may alternatively be specified as
+        <literal>prefer-secondary</literal>.
+        This parameter overrides any connection type specified by <literal>target_session_attrs</literal>.
+        If multiple hosts are specified in the connection string, each host is tried in the order given
+        until a connection is successful.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, then if the server is version 14
+        or greater, only a connection in which the server is not in recovery mode is considered
+        acceptable. The recovery mode state is determined by the value of the
+        <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection. Otherwise, if the server is prior to version 14, only a connection in
+        which read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions, the query
+        <literal>SHOW transaction_read_only</literal> will be sent upon any successful connection; if
+        it returns <literal>on</literal>, it means the server doesn't support read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, only a connection in which
+        the server is in recovery mode is considered acceptable. If the server is prior to version 14,
+        the query <literal>SELECT pg_is_in_recovery()</literal> will be sent upon any successful
+        connection; if it returns <literal>t</literal>, it means the server is in recovery mode.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, a connection in which
+        the server is in recovery mode is preferred. If no such connections can be found,
+        then a connection in which the server is not in recovery mode will be considered.
+       </para>
+
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
@@ -2130,14 +2201,16 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname> and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>in_recovery</varname> was not reported by releases before 14.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
@@ -7237,6 +7310,16 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
       linkend="libpq-connect-target-session-attrs"/> connection parameter.
      </para>
     </listitem>
+
+    <listitem>
+     <para>
+      <indexterm>
+       <primary><envar>PGTARGETSERVERTYPE</envar></primary>
+      </indexterm>
+      <envar>PGTARGETSERVERTYPE</envar> behaves the same as the <xref
+      linkend="libpq-connect-target-server-type"/> connection parameter.
+     </para>
+    </listitem>
    </itemizedlist>
   </para>
 
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 8b00235..36ac534 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,16 @@ SELCT 1/0;<!-- this typo is intentional -->
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname> and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>in_recovery</varname> was not reported by releases before 14.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 0a97b1d..f1c3e9d 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7943,6 +7943,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryState = RECOVERY_STATE_DONE;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index b448533..3917e24 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -3082,6 +3082,34 @@ TerminateOtherDBBackends(Oid databaseId)
 }
 
 /*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
+/*
  * ProcArraySetReplicationSlotXmin
  *
  * Install limits to future computations of the xmin horizon to prevent vacuum
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 4fa385b..957df0d 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -585,6 +585,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f522983..aa8841b 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -140,6 +140,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index c9424f1..6e0481e 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -162,6 +162,14 @@ static bool UseSemiNewlineNewline = false;	/* -j switch */
 static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
 
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
@@ -191,6 +199,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -539,6 +548,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -3009,6 +3022,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 }
 
 /*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* signal that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
+/*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
  * If an interrupt condition is pending, and it's safe to service it,
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index f4247ea..e8f9fd0 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -646,10 +646,13 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		/*
 		 * The postmaster already started the XLOG machinery, but we need to
 		 * call InitXLOGAccess(), if the system isn't in hot-standby mode.
-		 * This is handled by calling RecoveryInProgress and ignoring the
-		 * result.
+		 * This is handled by calling RecoveryInProgress.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index 416a087..a4ebcef 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_num \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 99a3e4f..6f65448 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -615,6 +615,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
+static bool in_recovery;
 
 
 /* should be static, but commands/variable.c needs to get at this */
@@ -1855,6 +1856,21 @@ static struct config_bool ConfigureNamesBool[] =
 	},
 
 	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"allow_system_table_mods", PGC_SUSET, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
 			NULL,
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index a5c7d0c..08b3b04 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -113,6 +113,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 extern void TerminateOtherDBBackends(Oid databaseId);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 5cb3969..6c243d4 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -43,6 +43,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index cfbe426..e5d42ac 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index bd30607..d29dd1f 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -68,6 +68,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7bee9dd..0005cf3 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -351,9 +351,14 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
+	{"target_server_type", "PGTARGETSERVERTYPE",
+		NULL, NULL,
+		"Target-Server-Type", "", 17, /* sizeof("prefer-secondary") = 17 */
+	offsetof(struct pg_conn, target_server_type)},
+
 	/* Terminating entry --- MUST BE LAST */
 	{NULL, NULL, NULL, NULL,
 	NULL, NULL, 0}
@@ -1001,6 +1006,30 @@ parse_comma_separated_list(char **startptr, bool *more)
 }
 
 /*
+ *		validateAndRecordTargetServerType
+ *
+ * Validate a given target server option value and record the requested server
+ * type. All valid target_server_type option values are also allowed in
+ * target_session_attrs (as a single option value).
+ *
+ * Returns true if OK, false if the specified option value is invalid.
+ */
+static bool
+validateAndRecordTargetServerType(const char *optionValue, TargetServerType *requestedServerType)
+{
+	if (strcmp(optionValue, "primary") == 0 || strcmp(optionValue, "read-write") == 0)
+		*requestedServerType = SERVER_TYPE_PRIMARY;
+	else if (strcmp(optionValue, "prefer-standby") == 0 || strcmp(optionValue, "prefer-secondary") == 0)
+		*requestedServerType = SERVER_TYPE_PREFER_STANDBY;
+	else if (strcmp(optionValue, "standby") == 0 || strcmp(optionValue, "secondary") == 0)
+		*requestedServerType = SERVER_TYPE_STANDBY;
+	else
+		return false;
+
+	return true;
+}
+
+/*
  *		connectOptions2
  *
  * Compute derived connection options after absorbing all user-supplied info.
@@ -1396,8 +1425,9 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (strcmp(conn->target_session_attrs, "any") == 0)
+			conn->requested_server_type = SERVER_TYPE_ANY;
+		else if (!validateAndRecordTargetServerType(conn->target_session_attrs, &conn->requested_server_type))
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
@@ -1409,6 +1439,23 @@ connectOptions2(PGconn *conn)
 	}
 
 	/*
+	 * Validate target_server_type option.
+	 * If a target_server_type is specified, it overrides any target server
+	 * type specified in target_session_attrs.
+	 */
+	if (conn->target_server_type)
+	{
+		if (!validateAndRecordTargetServerType(conn->target_server_type, &conn->requested_server_type))
+		{
+			conn->status = CONNECTION_BAD;
+			printfPQExpBuffer(&conn->errorMessage,
+							  libpq_gettext("invalid target_server_type value: \"%s\"\n"),
+							  conn->target_server_type);
+			return false;
+		}
+	}
+
+	/*
 	 * Only if we get this far is it appropriate to try to connect. (We need a
 	 * state flag, rather than just the boolean result of this function, in
 	 * case someone tries to PQreset() the PGconn.)
@@ -2228,6 +2275,110 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type. The connection state is set to
+ * try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedReadOrWriteConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_rw_host == -1)
+		conn->which_rw_host = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type (for recovery). The connection state
+ * is set to try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the read-write host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedRecoveryConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_rw_host == -1)
+		conn->which_rw_host = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -2310,6 +2461,7 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_CHECK_WRITABLE:
 		case CONNECTION_CONSUME:
 		case CONNECTION_GSS_STARTUP:
+		case CONNECTION_CHECK_RECOVERY:
 			break;
 
 		default:
@@ -2346,12 +2498,31 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->which_rw_host >= 0)
+			{
+				/*
+				 * Getting here means we failed to connect to read-only servers
+				 * and should now try to re-connect to a previously-connected-to
+				 * read-write server, whose host index is recorded in which_rw_host.
+				 */
+				conn->whichhost = conn->which_rw_host;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->which_rw_host = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
+		else
 		conn->whichhost++;
 
 		/* Drop any address info for previous host */
@@ -3560,38 +3731,102 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
+				 * If a primary (not-in-recovery / read-write) connection is
+				 * required, see if we have one.
 				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
-				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+				if ((conn->sversion >= 70400 &&
+					  (conn->requested_server_type == SERVER_TYPE_PRIMARY ||
+					   conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+					   conn->requested_server_type == SERVER_TYPE_STANDBY)))
+				{
+					if (conn->sversion < 140000)
+					{
+						/*
+						 * Save existing error messages across the PQsendQuery
+						 * attempt.  This is necessary because PQsendQuery is
+						 * going to reset conn->errorMessage, so we would lose
+						 * error messages related to previous hosts we have
+						 * tried and failed to connect to.
+						 */
+						if (!saveErrorMessage(conn, &savedMessage))
+							goto error_return;
+
+						conn->status = CONNECTION_OK;
+						if (!PQsendQuery(conn, "SHOW transaction_read_only"))
+						{
+							restoreErrorMessage(conn, &savedMessage);
+							goto error_return;
+						}
+						conn->status = CONNECTION_CHECK_WRITABLE;
+						restoreErrorMessage(conn, &savedMessage);
+						return PGRES_POLLING_READING;
+					}
+					else if ((conn->in_recovery &&
+						  conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						 (!conn->in_recovery &&
+						  (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						   conn->requested_server_type == SERVER_TYPE_STANDBY)))
+					{
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list
+						 * of connections, as it couldn't find any servers that
+						 * are in recovery.
+						 */
+						if (conn->which_rw_host == -2)
+							goto consume_checked_target_connection;
+
+						rejectCheckedRecoveryConnection(conn);
+						goto keep_going;
+					}
+
+					/* obtained the requested type, consume it */
+					goto consume_checked_target_connection;
+				}
+
+				/*
+				 * If the Requested type of connection is prefer-standby, then record
+				 * this host index and try other specified hosts before considering it later.
+				 * If the requested type of connection is standby, ignore this connection.
+				 */
+
+				if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+					conn->requested_server_type == SERVER_TYPE_STANDBY)
 				{
 					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
+					 * The following scenario is possible only for the
+					 * prefer-standby mode for the next pass of the list
+					 * of connections, as it couldn't find any servers that
+					 * are in recovery.
 					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
+					if (conn->which_rw_host == -2)
+						goto consume_checked_target_connection;
 
+					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					sendTerminateConn(conn);
+
+					/* Record read-write host index */
+					if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY)
 					{
-						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						if (conn->which_rw_host == -1)
+							conn->which_rw_host = conn->whichhost;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3690,42 +3925,149 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested server type is primary,
+					 * ignore it. Server is read-write and requested type is
+					 * prefer-standby, record it for the first time and try to
+					 * consume in the next scan (it means no standby server
+					 * was found in the first scan). Server is read-write and
+					 * requested type is standby, ignore this connection.
+					 */
+					if ((readonly_server &&
+						 conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						(!readonly_server &&
+						 (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						  conn->requested_server_type == SERVER_TYPE_STANDBY)))
 					{
-						/* Not writable; fail this connection. */
+						/*
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list of
+						 * connections, as it couldn't find any servers that
+						 * are default read-only.
+						 */
+						if (conn->which_rw_host == -2)
+							goto consume_checked_write_connection;
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
+						rejectCheckedReadOrWriteConnection(conn);
+						goto keep_going;
+					}
 
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
+			consume_checked_write_connection:
+					/* Session is requested type, so we're good. */
+					PQclear(res);
+					termPQExpBuffer(&savedMessage);
 
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
+					/*
+					 * Finish reading any remaining messages before being
+					 * considered as ready.
+					 */
+					conn->status = CONNECTION_CONSUME;
+					goto keep_going;
+				}
+
+				/*
+				 * Something went wrong with "SHOW transaction_read_only". We
+				 * should try next addresses.
+				 */
+				if (res)
+					PQclear(res);
+				restoreErrorMessage(conn, &savedMessage);
+
+				/* Append error report to conn->errorMessage. */
+				if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+					displayed_host = conn->connhost[conn->whichhost].hostaddr;
+				else
+					displayed_host = conn->connhost[conn->whichhost].host;
+				displayed_port = conn->connhost[conn->whichhost].port;
+				if (displayed_port == NULL || displayed_port[0] == '\0')
+					displayed_port = DEF_PGPORT_STR;
+				appendPQExpBuffer(&conn->errorMessage,
+								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+												"on server \"%s:%s\"\n"),
+								  displayed_host, displayed_port);
+
+				/* Close connection politely. */
+				conn->status = CONNECTION_OK;
+				sendTerminateConn(conn);
+
+				/* Try next address */
+				conn->try_next_addr = true;
+				goto keep_going;
+			}
+
+		case CONNECTION_CHECK_RECOVERY:
+			{
+				const char *displayed_host;
+				const char *displayed_port;
+
+				if (!saveErrorMessage(conn, &savedMessage))
+					goto error_return;
+
+				conn->status = CONNECTION_OK;
+				if (!PQconsumeInput(conn))
+				{
+					restoreErrorMessage(conn, &savedMessage);
+					goto error_return;
+				}
 
+				if (PQisBusy(conn))
+				{
+					conn->status = CONNECTION_CHECK_RECOVERY;
+					restoreErrorMessage(conn, &savedMessage);
+					return PGRES_POLLING_READING;
+				}
+
+				res = PQgetResult(conn);
+				if (res && (PQresultStatus(res) == PGRES_TUPLES_OK) &&
+					PQntuples(res) == 1)
+				{
+					char	   *val;
+					bool		standby_server;
+
+					val = PQgetvalue(res, 0, 0);
+					standby_server = (strncmp(val, "t", 1) == 0);
+
+					/*
+					 * Server is in recovery mode and requested type is
+					 * primary, ignore it. Server is not in recovery mode and
+					 * requested type is prefer-standby, record it for the
+					 * first time and try to consume in the next scan (it
+					 * means no standby server was found in the first scan).
+					 */
+					if ((standby_server &&
+						 conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+						(!standby_server &&
+						 (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						  conn->requested_server_type == SERVER_TYPE_STANDBY)))
+					{
 						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
+						 * The following scenario is possible only for the
+						 * prefer-standby type for the next pass of the list
+						 * of connections, as it couldn't find any servers that
+						 * are in recovery.
 						 */
-						conn->try_next_host = true;
+						if (conn->which_rw_host == -2)
+							goto consume_checked_recovery_connection;
+
+						/* Not a requested type; fail this connection. */
+						PQclear(res);
+						restoreErrorMessage(conn, &savedMessage);
+
+						rejectCheckedRecoveryConnection(conn);
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+			consume_checked_recovery_connection:
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3738,7 +4080,7 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/*
-				 * Something went wrong with "SHOW transaction_read_only". We
+				 * Something went wrong with "SELECT pg_is_in_recovery()". We
 				 * should try next addresses.
 				 */
 				if (res)
@@ -3754,7 +4096,7 @@ keep_going:						/* We will come back to here until there is
 				if (displayed_port == NULL || displayed_port[0] == '\0')
 					displayed_port = DEF_PGPORT_STR;
 				appendPQExpBuffer(&conn->errorMessage,
-								  libpq_gettext("test \"SHOW transaction_read_only\" failed "
+								  libpq_gettext("test \"SELECT pg_is_in_recovery()\" failed "
 												"on server \"%s:%s\"\n"),
 								  displayed_host, displayed_port);
 
@@ -3907,6 +4249,9 @@ makeEmptyPGconn(void)
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
 
+	conn->requested_server_type = SERVER_TYPE_ANY;
+	conn->which_rw_host = -1;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index eea0237..be73aa7 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1058,7 +1058,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1112,6 +1112,10 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 3b6a9fb..9c59feb 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -68,7 +68,8 @@ typedef enum
 	CONNECTION_CONSUME,			/* Wait for any pending message and consume
 								 * them. */
 	CONNECTION_GSS_STARTUP,		/* Negotiating GSSAPI. */
-	CONNECTION_CHECK_TARGET		/* Check if we have a proper target connection */
+	CONNECTION_CHECK_TARGET,	/* Check if we have a proper target connection */
+	CONNECTION_CHECK_RECOVERY	/* Check whether server is in recovery */
 } ConnStatusType;
 
 typedef enum
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 1de91ae..8033fc0 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -317,6 +317,15 @@ typedef struct pg_conn_host
 								 * found in password file. */
 } pg_conn_host;
 
+/* Target server type to connect to */
+typedef enum
+{
+	SERVER_TYPE_ANY = 0,           /* Any server (default) */
+	SERVER_TYPE_PRIMARY,           /* Primary server */
+	SERVER_TYPE_PREFER_STANDBY,    /* Prefer Standby server */
+	SERVER_TYPE_STANDBY            /* Standby server */
+} TargetServerType;
+
 /*
  * PGconn stores all the state data associated with a single connection
  * to a backend.
@@ -370,9 +379,33 @@ struct pg_conn
 	char	   *ssl_min_protocol_version;	/* minimum TLS protocol version */
 	char	   *ssl_max_protocol_version;	/* maximum TLS protocol version */
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values:
+	 * 	"any"
+	 * 	"primary" (or "read-write")
+	 * 	"prefer-standby" (or "prefer-secondary")
+	 * 	"standby" (or "secondary").
+	 */
 	char	   *target_session_attrs;
 
+	/*
+	 * Type of server to connect to. Possible values:
+	 * 	"primary" (or "read-write")
+	 * 	"prefer-standby" (or "prefer-secondary")
+	 * 	"standby" (or "secondary").
+	 * This overrides any connection type specified by target_session_attrs.
+	 * This option is almost a synonym for the target_session_attrs option, except
+	 * its purpose is to closely reflect the similar PGJDBC targetServerType option.
+	 * Note also that this option only accepts single option values, whereas in
+	 * future, target_session_attrs may accept multiple session attribute values.
+	 */
+	char	   *target_server_type;
+
+	/*
+	 * The requested server type, derived from target_session_attrs / target_server_type.
+	 */
+	TargetServerType requested_server_type;
+
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
 
@@ -406,6 +439,17 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * Index of the first read-write host encountered (if any) in the connection string.
+	 *
+	 * The initial value is -1, indicating that no read-write host has yet been found.
+	 * It is then set to the index of the first read-write host, if one is found in the
+	 * connection string during processing. If a second connection attempt is later made
+	 * to that read-write host, which_rw_host is then set to -2 to avoid recursion during
+	 * processing (and whichhost is set to the read-write host index).
+	 */
+	int			which_rw_host;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
@@ -436,6 +480,7 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
@@ -540,7 +585,6 @@ struct pg_cancel
 	int			be_key;			/* key of backend --- needed for cancels */
 };
 
-
 /* String descriptions of the ExecStatusTypes.
  * direct use of this array is deprecated; call PQresStatus() instead.
  */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 9e31a53..707d4ab 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 36;
+use Test::More tests => 62;
 
 # Initialize primary node
 my $node_primary = get_new_node('primary');
@@ -121,6 +121,150 @@ test_target_session_attrs($node_primary, $node_standby_1, $node_primary, "any",
 test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
 	"any", 0);
 
+# Connect to primary in "primary" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_primary,
+	"primary", 0);
+
+# Connect to primary in "primary" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_primary,
+	"primary", 0);
+
+# Connect to primary in "prefer-standby" mode with primary,primary list.
+test_target_session_attrs($node_primary, $node_primary, $node_primary,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to primary in "prefer-secondary" mode with primary,primary list.
+test_target_session_attrs($node_primary, $node_primary, $node_primary,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-ssecondary" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "standby" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "standby" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "secondary" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"secondary", 0);
+
+# Tests for connection parameter target_server_type
+note "testing connection parameter \"target_server_type\"";
+
+# Routine designed to run tests on the connection parameter
+# target_server_type with multiple nodes.
+sub test_target_server_type
+{
+	my $node1       = shift;
+	my $node2       = shift;
+	my $target_node = shift;
+	my $mode        = shift;
+	my $status      = shift;
+
+	my $node1_host = $node1->host;
+	my $node1_port = $node1->port;
+	my $node1_name = $node1->name;
+	my $node2_host = $node2->host;
+	my $node2_port = $node2->port;
+	my $node2_name = $node2->name;
+
+	my $target_name = $target_node->name;
+
+	# Build connection string for connection attempt.
+	my $connstr = "host=$node1_host,$node2_host ";
+	$connstr .= "port=$node1_port,$node2_port ";
+	$connstr .= "target_server_type=$mode";
+
+	# The client used for the connection does not matter, only the backend
+	# point does.
+	my ($ret, $stdout, $stderr) =
+	  $node1->psql('postgres', 'SHOW port;',
+		extra_params => [ '-d', $connstr ]);
+	is( $status == $ret && $stdout eq $target_node->port,
+		1,
+		"connect to node $target_name if mode \"$mode\" and $node1_name,$node2_name listed"
+	);
+
+	return;
+}
+
+# Connect to primary in "read-write" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_primary,
+	"read-write", 0);
+
+# Connect to primary in "read-write" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_primary,
+	"read-write", 0);
+
+# Connect to primary in "primary" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_primary,
+	"primary", 0);
+
+# Connect to primary in "primary" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_primary,
+	"primary", 0);
+
+# Connect to primary in "prefer-standby" mode with primary,primary list.
+test_target_server_type($node_primary, $node_primary, $node_primary,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to primary in "prefer-secondary" mode with primary,primary list.
+test_target_server_type($node_primary, $node_primary, $node_primary,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "standby" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "standby" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "secondary" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_standby_1,
+	"secondary", 0);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1

From c9da78a38611d1b3ac5d259d8c1d4ca01ac01658 Mon Sep 17 00:00:00 2001
From: Greg Nancarrow <gregn4422@gmail.com>
Date: Tue, 18 Aug 2020 20:48:43 +1000
Subject: [PATCH v18] Enhance libpq target_session_attrs and add
 target_server_type.

Enhance the connection parameter "target_session_attrs" to support new values
read-only/primary/standby/prefer-standby. To provide closer alignment with
similar functionality in the PGJDBC driver, add a new connection parameter
"target_server_type".

Add "in_recovery" as a GUC_REPORT variable, to update clients when the server
is in recovery mode. This improves the speed of client connections to a standby
server, by avoiding the need to execute a command to determine if the server is
in recovery mode. Similarly, enhance "transaction_read_only" to be a GUC_REPORT
variable, for client connections to read-only/read-write servers.

Add new SIGUSR1 handling interrupt to support reporting of recovery mode exit
to all backends and their respective clients.

Some parts of the code are taken from earlier development by
Elvis Pranskevichus and Tsunakawa Takayuki.

Discussion: https://www.postgresql.org/message-id/flat/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 contrib/postgres_fdw/expected/postgres_fdw.out |   2 +-
 doc/src/sgml/high-availability.sgml            |   5 +-
 doc/src/sgml/libpq.sgml                        | 105 +++++-
 doc/src/sgml/protocol.sgml                     |   9 +-
 src/backend/access/transam/xlog.c              |   3 +
 src/backend/storage/ipc/procarray.c            |  28 ++
 src/backend/storage/ipc/procsignal.c           |   3 +
 src/backend/storage/ipc/standby.c              |   9 +
 src/backend/tcop/postgres.c                    |  60 ++++
 src/backend/utils/init/postinit.c              |   9 +-
 src/backend/utils/misc/check_guc               |   2 +-
 src/backend/utils/misc/guc.c                   |  18 +-
 src/include/storage/procarray.h                |   1 +
 src/include/storage/procsignal.h               |   2 +
 src/include/storage/standby.h                  |   1 +
 src/include/tcop/tcopprot.h                    |   2 +
 src/interfaces/libpq/fe-connect.c              | 464 ++++++++++++++++++++++---
 src/interfaces/libpq/fe-exec.c                 |  10 +-
 src/interfaces/libpq/libpq-int.h               |  55 ++-
 src/test/recovery/t/001_stream_rep.pl          | 202 ++++++++++-
 20 files changed, 900 insertions(+), 90 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 90db550..ba0ba6e 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8898,7 +8898,7 @@ DO $d$
     END;
 $d$;
 ERROR:  invalid option "password"
-HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
+HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, target_server_type, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
 CONTEXT:  SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
 PL/pgSQL function inline_code_block line 3 at EXECUTE
 -- If we add a password for our user mapping instead, we should get a different
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index d6f79fc..afb80e6 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -1885,8 +1885,9 @@ if (!triggered)
    </para>
 
    <para>
-    During hot standby, the parameter <varname>transaction_read_only</varname> is always
-    true and may not be changed.  But as long as no attempt is made to modify
+    During hot standby, the parameters <varname>in_recovery</varname> and
+    <varname>transaction_read_only</varname> are always true and may not be
+    changed. But as long as no attempt is made to modify
     the database, connections during hot standby will act much like any other
     database connection.  If failover or switchover occurs, the database will
     switch to normal processing mode.  Sessions will remain connected while the
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index f7b765f..de31b34 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1811,18 +1811,81 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>target_session_attrs</literal></term>
       <listitem>
        <para>
-        If this parameter is set to <literal>read-write</literal>, only a
-        connection in which read-write transactions are accepted by default
-        is considered acceptable.  The query
-        <literal>SHOW transaction_read_only</literal> will be sent upon any
-        successful connection; if it returns <literal>on</literal>, the connection
-        will be closed.  If multiple hosts were specified in the connection
-        string, any remaining servers will be tried just as if the connection
-        attempt had failed.  The default value of this parameter,
-        <literal>any</literal>, regards all connections as acceptable.
-      </para>
+        The supported options for this parameter are <literal>any</literal>,
+        <literal>read-write</literal>, <literal>read-only</literal>,
+        <literal>primary</literal>, <literal>standby</literal> and
+        <literal>prefer-standby</literal>.
+        <literal>standby</literal> may alternatively be specified as <literal>secondary</literal>.
+        <literal>prefer-standby</literal> may alternatively be specified as
+        <literal>prefer-secondary</literal>.
+        The default value of this parameter, <literal>any</literal>, regards
+        all connections as acceptable. If multiple hosts are specified in the
+        connection string, each host is tried in the order given until a connection
+        is successful.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>read-write</literal>, only a connection in which
+        read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions, then if the server is version 14
+        or greater, the support of read-write transactions is determined by the value of the
+        <varname>transaction_read_only</varname> configuration parameter that is reported by
+        the server upon successful connection. Otherwise if the server is prior to version 14,
+        the query <literal>SHOW transaction_read_only</literal> will be sent upon any successful
+        connection; if it returns <literal>on</literal>, it means the server doesn't support
+        read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>read-only</literal>, only a connection
+        in which read-only transactions are accepted by default is considered acceptable.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>primary</literal>, then if the server is version 14
+        or greater, only a connection in which the server is not in recovery mode is considered
+        acceptable. The recovery mode state is determined by the value of the
+        <varname>in_recovery</varname> configuration parameter that is reported by the server upon
+        successful connection. Otherwise, if the server is prior to version 14, only a connection in
+        which read-write transactions are accepted by default is considered acceptable. To determine
+        whether the server supports read-write transactions (or only read-only transactions), the
+        query <literal>SHOW transaction_read_only</literal> will be sent upon any successful
+        connection; if it returns <literal>on</literal>, it means the server doesn't support
+        read-write transactions.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>standby</literal>, then if the server is version 14 or
+        greater, only a connection in which the server is in recovery mode is considered acceptable.
+        Otherwise, if the server is prior to version 14, only a connection for which the server only
+        supports read-only transactions is considered acceptable.
+       </para>
+
+       <para>
+        If this parameter is set to <literal>prefer-standby</literal>, then if the server is version
+        14 or greater, a connection in which the server is in recovery mode is preferred. Otherwise,
+        if the server is prior to version 14, a connection for which the server only supports
+        read-only transactions is preferred. If no such connections can be found, then a connection
+        in which the server is not in recovery mode (server is version 14 or greater) or a
+        connection for which the server supports read-write transactions (server is prior to version
+        14) will be considered.
+       </para>
+
       </listitem>
-    </varlistentry>
+     </varlistentry>
+
+     <varlistentry id="libpq-connect-target-server-type" xreflabel="target_server_type">
+      <term><literal>target_server_type</literal></term>
+      <listitem>
+       <para>
+        The purpose of this parameter is to reflect the similar PGJDBC <literal>targetServerType</literal>.
+        The supported options are a subset of those for <literal>target_session_attrs</literal>, namely
+        <literal>any</literal>, <literal>primary</literal>, <literal>secondary</literal> and
+        <literal>prefer-secondary</literal>. This parameter overrides any connection type specified by
+        <literal>target_session_attrs</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
   </sect2>
@@ -2130,14 +2193,18 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>DateStyle</varname>,
        <varname>IntervalStyle</varname>,
        <varname>TimeZone</varname>,
-       <varname>integer_datetimes</varname>, and
-       <varname>standard_conforming_strings</varname>.
+       <varname>integer_datetimes</varname>,
+       <varname>standard_conforming_strings</varname>,
+       <varname>transaction_read_only</varname>, and
+       <varname>in_recovery</varname>.
        (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
        <varname>integer_datetimes</varname> were not reported by releases before 8.0;
        <varname>standard_conforming_strings</varname> was not reported by releases
        before 8.1;
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-       <varname>application_name</varname> was not reported by releases before 9.0.)
+       <varname>application_name</varname> was not reported by releases before 9.0;
+       <varname>transaction_read_only</varname> and <varname>in_recovery</varname>
+       were not reported by releases before 14.0.)
        Note that
        <varname>server_version</varname>,
        <varname>server_encoding</varname> and
@@ -7237,6 +7304,16 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
       linkend="libpq-connect-target-session-attrs"/> connection parameter.
      </para>
     </listitem>
+
+    <listitem>
+     <para>
+      <indexterm>
+       <primary><envar>PGTARGETSERVERTYPE</envar></primary>
+      </indexterm>
+      <envar>PGTARGETSERVERTYPE</envar> behaves the same as the <xref
+      linkend="libpq-connect-target-server-type"/> connection parameter.
+     </para>
+    </listitem>
    </itemizedlist>
   </para>
 
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 8b00235..643d171 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1283,14 +1283,17 @@ SELCT 1/0;<!-- this typo is intentional -->
     <varname>DateStyle</varname>,
     <varname>IntervalStyle</varname>,
     <varname>TimeZone</varname>,
-    <varname>integer_datetimes</varname>, and
-    <varname>standard_conforming_strings</varname>.
+    <varname>integer_datetimes</varname>,
+    <varname>standard_conforming_strings</varname>,
+    <varname>transaction_read_only</varname>, and
+    <varname>in_recovery</varname>.
     (<varname>server_encoding</varname>, <varname>TimeZone</varname>, and
     <varname>integer_datetimes</varname> were not reported by releases before 8.0;
     <varname>standard_conforming_strings</varname> was not reported by releases
     before 8.1;
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
-    <varname>application_name</varname> was not reported by releases before 9.0.)
+    <varname>application_name</varname> was not reported by releases before 9.0;
+    <varname>transaction_read_only</varname> and <varname>in_recovery</varname> were not reported by releases before 14.0.)
     Note that
     <varname>server_version</varname>,
     <varname>server_encoding</varname> and
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 09c01ed..4129069 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7940,6 +7940,9 @@ StartupXLOG(void)
 	XLogCtl->SharedRecoveryState = RECOVERY_STATE_DONE;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	if (standbyState != STANDBY_DISABLED)
+		SendRecoveryExitSignal();
+
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index e687cde..0af2e30 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -3682,6 +3682,34 @@ TerminateOtherDBBackends(Oid databaseId)
 }
 
 /*
+ * SendSignalToAllBackends --- send a signal to all backends.
+ */
+void
+SendSignalToAllBackends(ProcSignalReason reason)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+	pid_t		pid = 0;
+
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		int			pgprocno = arrayP->pgprocnos[index];
+		volatile PGPROC *proc = &allProcs[pgprocno];
+		VirtualTransactionId procvxid;
+
+		GET_VXID_FROM_PGPROC(procvxid, *proc);
+
+		pid = proc->pid;
+		if (pid != 0)
+			(void) SendProcSignal(pid, reason, procvxid.backendId);
+	}
+
+	LWLockRelease(ProcArrayLock);
+}
+
+/*
  * ProcArraySetReplicationSlotXmin
  *
  * Install limits to future computations of the xmin horizon to prevent vacuum
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 4fa385b..957df0d 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -585,6 +585,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_RECOVERY_EXIT))
+		HandleRecoveryExitInterrupt();
+
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 52b2809..347b32d 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -140,6 +140,15 @@ ShutdownRecoveryTransactionEnvironment(void)
 	VirtualXactLockTableCleanup();
 }
 
+/*
+ * SendRecoveryExitSignal
+ *		Signal backends that the server has exited recovery mode.
+ */
+void
+SendRecoveryExitSignal(void)
+{
+	SendSignalToAllBackends(PROCSIG_RECOVERY_EXIT);
+}
 
 /*
  * -----------------------------------------------------
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index c9424f1..9fa16ec 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -163,6 +163,15 @@ static bool RecoveryConflictPending = false;
 static bool RecoveryConflictRetryable = true;
 static ProcSignalReason RecoveryConflictReason;
 
+/*
+ * Inbound recovery exit are initially processed by
+ * HandleRecoveryExitInterrupt(), called from inside a signal handler.
+ * That just sets the recoveryExitInterruptPending flag and sets the process
+ * latch. ProcessRecoveryExitInterrupt() will then be called whenever it's
+ * safe to actually deal with the interrupt.
+ */
+volatile sig_atomic_t recoveryExitInterruptPending = false;
+
 /* reused buffer to pass to SendRowDescriptionMessage() */
 static MemoryContext row_description_context = NULL;
 static StringInfoData row_description_buf;
@@ -191,6 +200,7 @@ static void drop_unnamed_stmt(void);
 static void log_disconnections(int code, Datum arg);
 static void enable_statement_timeout(void);
 static void disable_statement_timeout(void);
+static void ProcessRecoveryExitInterrupt(void);
 
 
 /* ----------------------------------------------------------------
@@ -539,6 +549,10 @@ ProcessClientReadInterrupt(bool blocked)
 		/* Process notify interrupts, if any */
 		if (notifyInterruptPending)
 			ProcessNotifyInterrupt();
+
+		/* Process recovery exit interrupts that happened while reading */
+		if (recoveryExitInterruptPending)
+			ProcessRecoveryExitInterrupt();
 	}
 	else if (ProcDiePending)
 	{
@@ -3009,6 +3023,52 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 }
 
 /*
+ * HandleRecoveryExitInterrupt
+ *
+ *		Signal handler portion of interrupt handling. Let the backend know
+ *		that the server has exited the recovery mode.
+ */
+void
+HandleRecoveryExitInterrupt(void)
+{
+	/*
+	 * Note: this is called by a SIGNAL HANDLER. You must be very wary what
+	 * you do here.
+	 */
+
+	/* flag that work needs to be done */
+	recoveryExitInterruptPending = true;
+
+	/* make sure the event is processed in due course */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ProcessRecoveryExitInterrupt
+ *
+ *		This is called just after waiting for a frontend command.  If a
+ *		interrupt arrives (via HandleRecoveryExitInterrupt()) while reading,
+ *		the read will be interrupted via the process's latch, and this routine
+ *		will get called.
+*/
+static void
+ProcessRecoveryExitInterrupt(void)
+{
+	recoveryExitInterruptPending = false;
+
+	SetConfigOption("in_recovery",
+					"off",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
+
+	/*
+	 * Flush output buffer so that clients receive the ParameterStatus message
+	 * as soon as possible.
+	 */
+	pq_flush();
+}
+
+
+/*
  * ProcessInterrupts: out-of-line portion of CHECK_FOR_INTERRUPTS() macro
  *
  * If an interrupt condition is pending, and it's safe to service it,
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index d4ab4c7..ce2d0b9 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -646,10 +646,13 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		/*
 		 * The postmaster already started the XLOG machinery, but we need to
 		 * call InitXLOGAccess(), if the system isn't in hot-standby mode.
-		 * This is handled by calling RecoveryInProgress and ignoring the
-		 * result.
+		 * This is handled by calling RecoveryInProgress.
 		 */
-		(void) RecoveryInProgress();
+		if (RecoveryInProgress())
+			SetConfigOption("in_recovery",
+							"on",
+							PGC_INTERNAL, PGC_S_OVERRIDE);
+
 	}
 	else
 	{
diff --git a/src/backend/utils/misc/check_guc b/src/backend/utils/misc/check_guc
index 416a087..a4ebcef 100755
--- a/src/backend/utils/misc/check_guc
+++ b/src/backend/utils/misc/check_guc
@@ -21,7 +21,7 @@ is_superuser lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time \
 pre_auth_delay role seed server_encoding server_version server_version_num \
 session_authorization trace_lock_oidmin trace_lock_table trace_locks trace_lwlocks \
 trace_notify trace_userlocks transaction_isolation transaction_read_only \
-zero_damaged_pages"
+zero_damaged_pages in_recovery"
 
 ### What options are listed in postgresql.conf.sample, but don't appear
 ### in guc.c?
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index de87ad6..f33cb68 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -615,6 +615,7 @@ static char *recovery_target_string;
 static char *recovery_target_xid_string;
 static char *recovery_target_name_string;
 static char *recovery_target_lsn_string;
+static bool in_recovery;
 
 
 /* should be static, but commands/variable.c needs to get at this */
@@ -1618,7 +1619,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_REPORT, GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
@@ -1845,6 +1846,21 @@ static struct config_bool ConfigureNamesBool[] =
 	},
 
 	{
+		/*
+		 * Not for general use --- used to indicate whether the instance is
+		 * recovery mode
+		 */
+		{"in_recovery", PGC_INTERNAL, UNGROUPED,
+			gettext_noop("Shows whether the instance is in recovery mode."),
+			NULL,
+			GUC_REPORT | GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&in_recovery,
+		false,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"allow_system_table_mods", PGC_SUSET, DEVELOPER_OPTIONS,
 			gettext_noop("Allows modifications of the structure of system tables."),
 			NULL,
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index ea8a876..d75db13 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -80,6 +80,7 @@ extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conf
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 								 int *nbackends, int *nprepared);
+extern void SendSignalToAllBackends(ProcSignalReason reason);
 extern void TerminateOtherDBBackends(Oid databaseId);
 
 extern void XidCacheRemoveRunningXids(TransactionId xid,
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 5cb3969..6c243d4 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -43,6 +43,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_RECOVERY_EXIT,		/* recovery exit interrupt */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index faaf1d3..d5c822d 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -26,6 +26,7 @@ extern int	max_standby_streaming_delay;
 
 extern void InitRecoveryTransactionEnvironment(void);
 extern void ShutdownRecoveryTransactionEnvironment(void);
+extern void SendRecoveryExitSignal(void);
 
 extern void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid,
 												RelFileNode node);
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index bd30607..d29dd1f 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -68,6 +68,8 @@ extern void StatementCancelHandler(SIGNAL_ARGS);
 extern void FloatExceptionHandler(SIGNAL_ARGS) pg_attribute_noreturn();
 extern void RecoveryConflictInterrupt(ProcSignalReason reason); /* called from SIGUSR1
 																 * handler */
+/* recovery exit interrupt handling function */
+extern void HandleRecoveryExitInterrupt(void);
 extern void ProcessClientReadInterrupt(bool blocked);
 extern void ProcessClientWriteInterrupt(bool blocked);
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7bee9dd..4326580 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -351,9 +351,14 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 
 	{"target_session_attrs", "PGTARGETSESSIONATTRS",
 		DefaultTargetSessionAttrs, NULL,
-		"Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */
+		"Target-Session-Attrs", "", 15, /* sizeof("prefer-standby") = 15 */
 	offsetof(struct pg_conn, target_session_attrs)},
 
+	{"target_server_type", "PGTARGETSERVERTYPE",
+		NULL, NULL,
+		"Target-Server-Type", "", 17,	/* sizeof("prefer-secondary") = 17 */
+	offsetof(struct pg_conn, target_server_type)},
+
 	/* Terminating entry --- MUST BE LAST */
 	{NULL, NULL, NULL, NULL,
 	NULL, NULL, 0}
@@ -1001,6 +1006,58 @@ parse_comma_separated_list(char **startptr, bool *more)
 }
 
 /*
+ *		validateAndGetTargetServerType
+ *
+ * Validate a given target_server_type option value and get the requested server type.
+ *
+ * Returns true if OK, false if the specified option value is invalid.
+ */
+static bool
+validateAndGetTargetServerType(const char *optionValue, TargetServerType *requestedServerType)
+{
+	if (strcmp(optionValue, "any") == 0)
+		*requestedServerType = SERVER_TYPE_ANY;
+	else if (strcmp(optionValue, "primary") == 0)
+		*requestedServerType = SERVER_TYPE_PRIMARY;
+	else if (strcmp(optionValue, "prefer-secondary") == 0)
+		*requestedServerType = SERVER_TYPE_PREFER_STANDBY;
+	else if (strcmp(optionValue, "secondary") == 0)
+		*requestedServerType = SERVER_TYPE_STANDBY;
+	else
+		return false;
+
+	return true;
+}
+
+/*
+ *		validateAndGetTargetServerTypeFromSessionAttrs
+ *
+ * Validate a given target_session_attrs value and get the requested server type.
+ * All valid target_server_type option values are also allowed in target_session_attrs
+ * (as a single option value).
+ *
+ * Returns true if OK, false if the specified option value is invalid.
+ */
+static bool
+validateAndGetTargetServerTypeFromSessionAttrs(const char *optionValue, TargetServerType *requestedServerType)
+{
+	if (!validateAndGetTargetServerType(optionValue, requestedServerType))
+	{
+		if (strcmp(optionValue, "read-write") == 0)
+			*requestedServerType = SERVER_TYPE_READ_WRITE;
+		else if (strcmp(optionValue, "read-only") == 0)
+			*requestedServerType = SERVER_TYPE_READ_ONLY;
+		else if (strcmp(optionValue, "prefer-standby") == 0)
+			*requestedServerType = SERVER_TYPE_PREFER_STANDBY;
+		else if (strcmp(optionValue, "standby") == 0)
+			*requestedServerType = SERVER_TYPE_STANDBY;
+		else
+			return false;
+	}
+	return true;
+}
+
+/*
  *		connectOptions2
  *
  * Compute derived connection options after absorbing all user-supplied info.
@@ -1396,19 +1453,36 @@ connectOptions2(PGconn *conn)
 	 */
 	if (conn->target_session_attrs)
 	{
-		if (strcmp(conn->target_session_attrs, "any") != 0
-			&& strcmp(conn->target_session_attrs, "read-write") != 0)
+		if (!validateAndGetTargetServerTypeFromSessionAttrs(conn->target_session_attrs, &conn->requested_server_type))
 		{
 			conn->status = CONNECTION_BAD;
 			printfPQExpBuffer(&conn->errorMessage,
 							  libpq_gettext("invalid %s value: \"%s\"\n"),
-							  "target_settion_attrs",
+							  "target_session_attrs",
 							  conn->target_session_attrs);
 			return false;
 		}
 	}
 
 	/*
+	 * Validate target_server_type option. If a target_server_type is
+	 * specified, it overrides any target server type specified in
+	 * target_session_attrs.
+	 */
+	if (conn->target_server_type)
+	{
+		if (!validateAndGetTargetServerType(conn->target_server_type, &conn->requested_server_type))
+		{
+			conn->status = CONNECTION_BAD;
+			printfPQExpBuffer(&conn->errorMessage,
+							  libpq_gettext("invalid %s value: \"%s\"\n"),
+							  "target_server_type",
+							  conn->target_server_type);
+			return false;
+		}
+	}
+
+	/*
 	 * Only if we get this far is it appropriate to try to connect. (We need a
 	 * state flag, rather than just the boolean result of this function, in
 	 * case someone tries to PQreset() the PGconn.)
@@ -2228,6 +2302,116 @@ restoreErrorMessage(PGconn *conn, PQExpBuffer savedMessage)
 	termPQExpBuffer(savedMessage);
 }
 
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type (read-write/read-only).
+ * The connection state is set to try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the read-write host-index
+ * hasn't been set, then it is set to the index of this connection's host, so
+ * that a connection to this host can be made again in the event that no
+ * connection to a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedReadOrWriteConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a writable "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("could not make a readonly "
+										"connection to server "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record read-write host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_primary_or_rw_host == -1)
+	{
+		/*
+		 * This can only happen if server version < 14 (for which standby
+		 * is regarded as read-only)
+		 */
+		conn->which_primary_or_rw_host = conn->whichhost;
+	}
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
+/*
+ * Internal helper function used for rejecting (and closing) a connection that
+ * doesn't satisfy the requested server type (for recovery). The connection state
+ * is set to try the next host (if any).
+ * In the case of SERVER_TYPE_PREFER_STANDBY, if the primary host-index hasn't
+ * been set, then it is set to the index of this connection's host, so that a
+ * connection to this host can be made again in the event that no connection to
+ * a standby host could be made after the first host scan.
+ */
+static void
+rejectCheckedRecoveryConnection(PGconn *conn)
+{
+	/* Not a requested type; fail this connection. */
+	const char *displayed_host;
+	const char *displayed_port;
+
+	/* Append error report to conn->errorMessage. */
+	if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
+		displayed_host = conn->connhost[conn->whichhost].hostaddr;
+	else
+		displayed_host = conn->connhost[conn->whichhost].host;
+	displayed_port = conn->connhost[conn->whichhost].port;
+	if (displayed_port == NULL || displayed_port[0] == '\0')
+		displayed_port = DEF_PGPORT_STR;
+
+	if (conn->requested_server_type == SERVER_TYPE_PRIMARY)
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+	else
+		appendPQExpBuffer(&conn->errorMessage,
+						  libpq_gettext("server is not in recovery mode "
+										"\"%s:%s\"\n"),
+						  displayed_host, displayed_port);
+
+	/* Close connection politely. */
+	conn->status = CONNECTION_OK;
+	sendTerminateConn(conn);
+
+	/* Record primary host index */
+	if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY && conn->which_primary_or_rw_host == -1)
+		conn->which_primary_or_rw_host = conn->whichhost;
+
+	/*
+	 * Try next host if any, but we don't want to consider additional
+	 * addresses for this host.
+	 */
+	conn->try_next_host = true;
+}
+
 /* ----------------
  *		PQconnectPoll
  *
@@ -2346,13 +2530,34 @@ keep_going:						/* We will come back to here until there is
 
 		if (conn->whichhost + 1 >= conn->nconnhost)
 		{
-			/*
-			 * Oops, no more hosts.  An appropriate error message is already
-			 * set up, so just set the right status.
-			 */
-			goto error_return;
+			if (conn->which_primary_or_rw_host >= 0)
+			{
+				/*
+				 * Getting here means we failed to connect to standby servers
+				 * (or to read-only servers for server verson < 14) and should
+				 * now try to re-connect to a previously-connected-to primary
+				 * server (or read-write server for server version < 14),
+				 * whose host index is recorded in which_primary_or_rw_host.
+				 */
+				conn->whichhost = conn->which_primary_or_rw_host;
+
+				/*
+				 * Reset the host index value to avoid recursion during the
+				 * second connection attempt.
+				 */
+				conn->which_primary_or_rw_host = -2;
+			}
+			else
+			{
+				/*
+				 * Oops, no more hosts.  An appropriate error message is
+				 * already set up, so just set the right status.
+				 */
+				goto error_return;
+			}
 		}
-		conn->whichhost++;
+		else
+			conn->whichhost++;
 
 		/* Drop any address info for previous host */
 		release_conn_addrinfo(conn);
@@ -3560,38 +3765,169 @@ keep_going:						/* We will come back to here until there is
 		case CONNECTION_CHECK_TARGET:
 			{
 				/*
-				 * If a read-write connection is required, see if we have one.
-				 *
 				 * Servers before 7.4 lack the transaction_read_only GUC, but
 				 * by the same token they don't have any read-only mode, so we
 				 * may just skip the test in that case.
 				 */
-				if (conn->sversion >= 70400 &&
-					conn->target_session_attrs != NULL &&
-					strcmp(conn->target_session_attrs, "read-write") == 0)
+				if (conn->sversion >= 70400)
 				{
 					/*
-					 * Save existing error messages across the PQsendQuery
-					 * attempt.  This is necessary because PQsendQuery is
-					 * going to reset conn->errorMessage, so we would lose
-					 * error messages related to previous hosts we have tried
-					 * and failed to connect to.
+					 * If a read-write or read-only connection is required,
+					 * see if we have one.
 					 */
-					if (!saveErrorMessage(conn, &savedMessage))
-						goto error_return;
+					if (conn->requested_server_type == SERVER_TYPE_READ_WRITE ||
+						conn->requested_server_type == SERVER_TYPE_READ_ONLY)
+					{
+						if (conn->sversion < 140000)
+						{
+							/*
+							 * Save existing error messages across the
+							 * PQsendQuery attempt.  This is necessary because
+							 * PQsendQuery is going to reset
+							 * conn->errorMessage, so we would lose error
+							 * messages related to previous hosts we have
+							 * tried and failed to connect to.
+							 */
+							if (!saveErrorMessage(conn, &savedMessage))
+								goto error_return;
+
+							conn->status = CONNECTION_OK;
+							if (!PQsendQuery(conn, "SHOW transaction_read_only"))
+							{
+								restoreErrorMessage(conn, &savedMessage);
+								goto error_return;
+							}
+							conn->status = CONNECTION_CHECK_WRITABLE;
+							restoreErrorMessage(conn, &savedMessage);
+							return PGRES_POLLING_READING;
+						}
+						else if ((conn->transaction_read_only &&
+								  conn->requested_server_type == SERVER_TYPE_READ_WRITE) ||
+								 (!conn->transaction_read_only &&
+								  conn->requested_server_type == SERVER_TYPE_READ_ONLY))
+						{
+							/*
+							 * Server is read-only but requested read-write,
+							 * or server is read-write but requested
+							 * read-only, reject and continue to process any
+							 * further hosts ...
+							 */
+
+							rejectCheckedReadOrWriteConnection(conn);
+							goto keep_going;
+						}
+
+						/* obtained the requested type, consume it */
+						goto consume_checked_target_connection;
+					}
+					else if (conn->requested_server_type == SERVER_TYPE_PRIMARY ||
+							 conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+							 conn->requested_server_type == SERVER_TYPE_STANDBY)
+					{
+						if (conn->sversion < 140000)
+						{
+							/*
+							 * Save existing error messages across the
+							 * PQsendQuery attempt.  This is necessary because
+							 * PQsendQuery is going to reset
+							 * conn->errorMessage, so we would lose error
+							 * messages related to previous hosts we have
+							 * tried and failed to connect to.
+							 */
+							if (!saveErrorMessage(conn, &savedMessage))
+								goto error_return;
+
+							conn->status = CONNECTION_OK;
+							if (!PQsendQuery(conn, "SHOW transaction_read_only"))
+							{
+								restoreErrorMessage(conn, &savedMessage);
+								goto error_return;
+							}
+							conn->status = CONNECTION_CHECK_WRITABLE;
+							restoreErrorMessage(conn, &savedMessage);
+							return PGRES_POLLING_READING;
+						}
+						else if ((conn->in_recovery &&
+								  conn->requested_server_type == SERVER_TYPE_PRIMARY) ||
+								 (!conn->in_recovery &&
+								  (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+								   conn->requested_server_type == SERVER_TYPE_STANDBY)))
+						{
+							/*
+							 * Server is in recovery but requested primary, or
+							 * server is not in recovery but requested
+							 * prefer-standby/standby.
+							 */
+
+							if (conn->which_primary_or_rw_host == -2)
+							{
+								/*
+								 * This scenario is possible only for the
+								 * prefer-standby type for the next pass of
+								 * the list of connections as it couldn't find
+								 * any servers that are in recovery.
+								 */
+								goto consume_checked_target_connection;
+							}
+
+							/*
+							 * Reject and continue to process any further
+							 * hosts ...
+							 */
 
+							rejectCheckedRecoveryConnection(conn);
+							goto keep_going;
+						}
+
+						/* obtained the requested type, consume it */
+						goto consume_checked_target_connection;
+					}
+				}
+
+				/*
+				 * For servers before 7.4 (which don't support read-only), if
+				 * the requested type of connection is prefer-standby, then
+				 * record this host index and try other specified hosts before
+				 * considering it later. If the requested type of connection
+				 * is read-only or standby, ignore this connection.
+				 */
+
+				if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+					conn->requested_server_type == SERVER_TYPE_READ_ONLY ||
+					conn->requested_server_type == SERVER_TYPE_STANDBY)
+				{
+					if (conn->which_primary_or_rw_host == -2)
+					{
+						/*
+						 * This scenario is possible only for the
+						 * prefer-standby type for the next pass of the list
+						 * of connections as it couldn't find any servers that
+						 * are read-only.
+						 */
+						goto consume_checked_target_connection;
+					}
+
+					/* Close connection politely. */
 					conn->status = CONNECTION_OK;
-					if (!PQsendQuery(conn,
-									 "SHOW transaction_read_only"))
+					sendTerminateConn(conn);
+
+					/* Record host index */
+					if (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY)
 					{
-						restoreErrorMessage(conn, &savedMessage);
-						goto error_return;
+						if (conn->which_primary_or_rw_host == -1)
+							conn->which_primary_or_rw_host = conn->whichhost;
 					}
-					conn->status = CONNECTION_CHECK_WRITABLE;
-					restoreErrorMessage(conn, &savedMessage);
-					return PGRES_POLLING_READING;
+
+					/*
+					 * Try next host if any, but we don't want to consider
+					 * additional addresses for this host.
+					 */
+					conn->try_next_host = true;
+					goto keep_going;
 				}
 
+		consume_checked_target_connection:
+
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
@@ -3663,6 +3999,7 @@ keep_going:						/* We will come back to here until there is
 				conn->status = CONNECTION_OK;
 				return PGRES_POLLING_OK;
 			}
+
 		case CONNECTION_CHECK_WRITABLE:
 			{
 				const char *displayed_host;
@@ -3690,42 +4027,51 @@ keep_going:						/* We will come back to here until there is
 					PQntuples(res) == 1)
 				{
 					char	   *val;
+					bool		readonly_server;
 
 					val = PQgetvalue(res, 0, 0);
-					if (strncmp(val, "on", 2) == 0)
+					readonly_server = (strncmp(val, "on", 2) == 0);
+
+					/*
+					 * Server is read-only and requested server type is
+					 * read-write (or requested server type is primary and
+					 * server version < 14), ignore this connection. Server is
+					 * read-write and requested type is read-only (or
+					 * requested server type is standby and server version <
+					 * 14), ignore this connection. Server is read-write
+					 * (version < 14) and requested type is prefer-standby,
+					 * record it for the first time and try to consume in the
+					 * next scan (it means no read-only server is found in the
+					 * first scan).
+					 */
+					if ((readonly_server &&
+						 (conn->requested_server_type == SERVER_TYPE_READ_WRITE ||
+						  conn->requested_server_type == SERVER_TYPE_PRIMARY)) ||
+						(!readonly_server &&
+						 (conn->requested_server_type == SERVER_TYPE_PREFER_STANDBY ||
+						  conn->requested_server_type == SERVER_TYPE_READ_ONLY ||
+						  conn->requested_server_type == SERVER_TYPE_STANDBY)))
 					{
-						/* Not writable; fail this connection. */
+						if (conn->which_primary_or_rw_host == -2)
+						{
+							/*
+							 * This scenario is possible only for the
+							 * prefer-standby type for the next pass of the
+							 * list of connections as it couldn't find any
+							 * servers that are read-only.
+							 */
+							goto consume_checked_target_connection;
+						}
+
+						/* Not a requested type; fail this connection. */
 						PQclear(res);
 						restoreErrorMessage(conn, &savedMessage);
 
-						/* Append error report to conn->errorMessage. */
-						if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS)
-							displayed_host = conn->connhost[conn->whichhost].hostaddr;
-						else
-							displayed_host = conn->connhost[conn->whichhost].host;
-						displayed_port = conn->connhost[conn->whichhost].port;
-						if (displayed_port == NULL || displayed_port[0] == '\0')
-							displayed_port = DEF_PGPORT_STR;
-
-						appendPQExpBuffer(&conn->errorMessage,
-										  libpq_gettext("could not make a writable "
-														"connection to server "
-														"\"%s:%s\"\n"),
-										  displayed_host, displayed_port);
-
-						/* Close connection politely. */
-						conn->status = CONNECTION_OK;
-						sendTerminateConn(conn);
-
-						/*
-						 * Try next host if any, but we don't want to consider
-						 * additional addresses for this host.
-						 */
-						conn->try_next_host = true;
+						rejectCheckedReadOrWriteConnection(conn);
 						goto keep_going;
 					}
 
-					/* Session is read-write, so we're good. */
+					/* Session is requested type, so we're good. */
 					PQclear(res);
 					termPQExpBuffer(&savedMessage);
 
@@ -3903,10 +4249,14 @@ makeEmptyPGconn(void)
 	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
+	conn->transaction_read_only = false;
 	conn->verbosity = PQERRORS_DEFAULT;
 	conn->show_context = PQSHOW_CONTEXT_ERRORS;
 	conn->sock = PGINVALID_SOCKET;
 
+	conn->requested_server_type = SERVER_TYPE_ANY;
+	conn->which_primary_or_rw_host = -1;
+
 	/*
 	 * We try to send at least 8K at a time, which is the usual size of pipe
 	 * buffers on Unix systems.  That way, when we are sending a large amount
@@ -4075,6 +4425,8 @@ freePGconn(PGconn *conn)
 		free(conn->rowBuf);
 	if (conn->target_session_attrs)
 		free(conn->target_session_attrs);
+	if (conn->target_server_type)
+		free(conn->target_server_type);
 	termPQExpBuffer(&conn->errorMessage);
 	termPQExpBuffer(&conn->workBuffer);
 
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index eea0237..0605b23 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1058,7 +1058,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 	}
 
 	/*
-	 * Special hacks: remember client_encoding and
+	 * Special hacks: remember client_encoding, transaction_read_only and
 	 * standard_conforming_strings, and convert server version to a numeric
 	 * form.  We keep the first two of these in static variables as well, so
 	 * that PQescapeString and PQescapeBytea can behave somewhat sanely (at
@@ -1112,6 +1112,14 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
 		else
 			conn->sversion = 0; /* unknown */
 	}
+	else if (strcmp(name, "transaction_read_only") == 0)
+	{
+		conn->transaction_read_only = (strcmp(value, "on") == 0);
+	}
+	else if (strcmp(name, "in_recovery") == 0)
+	{
+		conn->in_recovery = (strcmp(value, "on") == 0);
+	}
 }
 
 
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 1de91ae..13376ee 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -317,6 +317,17 @@ typedef struct pg_conn_host
 								 * found in password file. */
 } pg_conn_host;
 
+/* Target server type to connect to */
+typedef enum
+{
+	SERVER_TYPE_ANY = 0,		/* Any server (default) */
+	SERVER_TYPE_READ_WRITE,		/* Read-write server */
+	SERVER_TYPE_READ_ONLY,		/* Read-only server */
+	SERVER_TYPE_PRIMARY,		/* Primary server */
+	SERVER_TYPE_PREFER_STANDBY,	/* Prefer Standby server */
+	SERVER_TYPE_STANDBY		/* Standby server */
+} TargetServerType;
+
 /*
  * PGconn stores all the state data associated with a single connection
  * to a backend.
@@ -370,9 +381,30 @@ struct pg_conn
 	char	   *ssl_min_protocol_version;	/* minimum TLS protocol version */
 	char	   *ssl_max_protocol_version;	/* maximum TLS protocol version */
 
-	/* Type of connection to make.  Possible values: any, read-write. */
+	/*
+	 * Type of connection to make.  Possible values: "any", "read-write",
+	 * "read-only", "primary", "prefer-standby" (or "prefer-secondary"),
+	 * "standby" (or "secondary").
+	 */
 	char	   *target_session_attrs;
 
+	/*
+	 * Type of server to connect to. Possible values: "any", "primary",
+	 * "prefer-secondary", "secondary" This overrides any connection type
+	 * specified by target_session_attrs. This option supports a subset of the
+	 * target_session_attrs option values, and its purpose is to closely
+	 * reflect the similar PGJDBC targetServerType option. Note also that this
+	 * option only accepts single option values, whereas in future,
+	 * target_session_attrs may accept multiple session attribute values.
+	 */
+	char	   *target_server_type;
+
+	/*
+	 * The requested server type, derived from target_session_attrs /
+	 * target_server_type.
+	 */
+	TargetServerType requested_server_type;
+
 	/* Optional file to write trace info to */
 	FILE	   *Pfdebug;
 
@@ -406,6 +438,24 @@ struct pg_conn
 	pg_conn_host *connhost;		/* details about each named host */
 	char	   *connip;			/* IP address for current network connection */
 
+	/*
+	 * Index of the first primary host (or read-write host if server version
+	 * < 14) encountered (if any) in the connection string. This is used
+	 * during processing of requested server connection type
+	 * SERVER_TYPE_PREFER_STANDBY.
+	 *
+	 * The initial value is -1, indicating that no primary host has yet been
+	 * found. It is then set to the index of the first primary host, if one is
+	 * found in the connection string during processing. If a second
+	 * connection attempt is later made to that primary host (because no
+	 * connection to a standby server could be made), which_primary_or_rw_host
+	 * is then set to -2 to avoid recursion during subsequent processing (and
+	 * whichhost is set to the primary host index). Note that for server
+	 * versions < 14, a requested type of "primary" is regarded as
+	 * "read-write" and "standby" is regarded as "read-only".
+	 */
+	int		which_primary_or_rw_host;
+
 	/* Connection data */
 	pgsocket	sock;			/* FD for socket, PGINVALID_SOCKET if
 								 * unconnected */
@@ -436,6 +486,8 @@ struct pg_conn
 	pgParameterStatus *pstatus; /* ParameterStatus data */
 	int			client_encoding;	/* encoding id */
 	bool		std_strings;	/* standard_conforming_strings */
+	bool		transaction_read_only;	/* transaction_read_only */
+	bool		in_recovery;	/* in_recovery */
 	PGVerbosity verbosity;		/* error/notice message verbosity */
 	PGContextVisibility show_context;	/* whether to show CONTEXT field */
 	PGlobjfuncs *lobjfuncs;		/* private state for large-object access fns */
@@ -540,7 +592,6 @@ struct pg_cancel
 	int			be_key;			/* key of backend --- needed for cancels */
 };
 
-
 /* String descriptions of the ExecStatusTypes.
  * direct use of this array is deprecated; call PQresStatus() instead.
  */
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 9e31a53..a1e59c4 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 36;
+use Test::More tests => 66;
 
 # Initialize primary node
 my $node_primary = get_new_node('primary');
@@ -85,7 +85,7 @@ sub test_target_session_attrs
 	my $node2_port = $node2->port;
 	my $node2_name = $node2->name;
 
-	my $target_name = $target_node->name;
+	my $target_name = $target_node->name if (defined $target_node);
 
 	# Build connection string for connection attempt.
 	my $connstr = "host=$node1_host,$node2_host ";
@@ -97,10 +97,25 @@ sub test_target_session_attrs
 	my ($ret, $stdout, $stderr) =
 	  $node1->psql('postgres', 'SHOW port;',
 		extra_params => [ '-d', $connstr ]);
-	is( $status == $ret && $stdout eq $target_node->port,
-		1,
-		"connect to node $target_name if mode \"$mode\" and $node1_name,$node2_name listed"
-	);
+	if ($status == 0)
+	{
+		is( $status == $ret && $stdout eq $target_node->port,
+			1,
+			"connect to node $target_name if mode \"$mode\" and $node1_name,$node2_name listed"
+		);
+	}
+	else
+	{
+		print "status = $status\n";
+		print "ret = $ret\n";
+		print "stdout = $stdout\n";
+		print "stderr = $stderr\n";
+
+		is( $status == $ret,
+			1,
+			"fail to connect to any nodes if mode \"$mode\" and $node1_name,$node2_name listed"
+		);
+	}
 
 	return;
 }
@@ -121,6 +136,181 @@ test_target_session_attrs($node_primary, $node_standby_1, $node_primary, "any",
 test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
 	"any", 0);
 
+# Connect to primary in "primary" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_primary,
+	"primary", 0);
+
+# Connect to primary in "primary" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_primary,
+	"primary", 0);
+
+# Connect to standby1 in "read-only" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"read-only", 0);
+
+# Connect to standby1 in "read-only" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"read-only", 0);
+
+# Connect to primary in "prefer-standby" mode with primary,primary list.
+test_target_session_attrs($node_primary, $node_primary, $node_primary,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to standby1 in "prefer-standby" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"prefer-standby", 0);
+
+# Connect to primary in "prefer-secondary" mode with primary,primary list.
+test_target_session_attrs($node_primary, $node_primary, $node_primary,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-ssecondary" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "standby" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "standby" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"standby", 0);
+
+# Connect to standby1 in "secondary" mode with primary,standby1 list.
+test_target_session_attrs($node_primary, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,primary list.
+test_target_session_attrs($node_standby_1, $node_primary, $node_standby_1,
+	"secondary", 0);
+
+# Fail to connect in "read-write" mode with standby1,standby2 list.
+test_target_session_attrs($node_standby_1, $node_standby_2, undef,
+	"read-write", 2);
+
+# Fail to connect in "primary" mode with standby1,standby2 list.
+test_target_session_attrs($node_standby_1, $node_standby_2, undef,
+	"primary", 2);
+
+# Fail to connect in "read-only" mode with primary,primary list.
+test_target_session_attrs($node_primary, $node_primary, undef,
+	"read-only", 2);
+
+# Fail to connect in "standby" mode with primary,primary list.
+test_target_session_attrs($node_primary, $node_primary, undef,
+	"standby", 2);
+
+# Fail to connect in "secondary" mode with primary,primary list.
+test_target_session_attrs($node_primary, $node_primary, undef,
+	"secondary", 2);
+
+# Tests for connection parameter target_server_type
+note "testing connection parameter \"target_server_type\"";
+
+# Routine designed to run tests on the connection parameter
+# target_server_type with multiple nodes.
+sub test_target_server_type
+{
+	my $node1       = shift;
+	my $node2       = shift;
+	my $target_node = shift;
+	my $mode        = shift;
+	my $status      = shift;
+
+	my $node1_host = $node1->host;
+	my $node1_port = $node1->port;
+	my $node1_name = $node1->name;
+	my $node2_host = $node2->host;
+	my $node2_port = $node2->port;
+	my $node2_name = $node2->name;
+
+	my $target_name = $target_node->name if (defined $target_node);
+
+	# Build connection string for connection attempt.
+	my $connstr = "host=$node1_host,$node2_host ";
+	$connstr .= "port=$node1_port,$node2_port ";
+	$connstr .= "target_server_type=$mode";
+
+	# The client used for the connection does not matter, only the backend
+	# point does.
+	my ($ret, $stdout, $stderr) =
+	  $node1->psql('postgres', 'SHOW port;',
+		extra_params => [ '-d', $connstr ]);
+	if ($status == 0)
+	{
+		is( $status == $ret && $stdout eq $target_node->port,
+			1,
+			"connect to node $target_name if mode \"$mode\" and $node1_name,$node2_name listed"
+		);
+	}
+	else
+	{
+		print "status = $status\n";
+		print "ret = $ret\n";
+		print "stdout = $stdout\n";
+		print "stderr = $stderr\n";
+
+		is( $status == $ret,
+			1,
+			"fail to connect to any nodes if mode \"$mode\" and $node1_name,$node2_name listed"
+		);
+	}
+
+	return;
+}
+
+# Connect to primary in "any" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_primary, "any",
+	0);
+
+# Connect to standby1 in "any" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_standby_1,
+	"any", 0);
+
+# Connect to primary in "primary" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_primary,
+	"primary", 0);
+
+# Connect to primary in "primary" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_primary,
+	"primary", 0);
+
+# Connect to primary in "prefer-secondary" mode with primary,primary list.
+test_target_server_type($node_primary, $node_primary, $node_primary,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "prefer-secondary" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_standby_1,
+	"prefer-secondary", 0);
+
+# Connect to standby1 in "secondary" mode with primary,standby1 list.
+test_target_server_type($node_primary, $node_standby_1, $node_standby_1,
+	"secondary", 0);
+
+# Connect to standby1 in "secondary" mode with standby1,primary list.
+test_target_server_type($node_standby_1, $node_primary, $node_standby_1,
+	"secondary", 0);
+
+# Fail to connect in "primary" mode with standby1,standby2 list.
+test_target_server_type($node_standby_1, $node_standby_2, undef,
+	"primary", 2);
+
+# Fail to connect in "secondary" mode with primary,primary list.
+test_target_server_type($node_primary, $node_primary, undef,
+	"secondary", 2);
+
 # Test for SHOW commands using a WAL sender connection with a replication
 # role.
 note "testing SHOW commands for replication connection";
-- 
1.8.3.1