Add DBState to pg_control_system function

From b23f134363d33040249ca3c09b3d5de23aae5792 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Tue, 1 Feb 2022 04:16:52 +0000
Subject: [PATCH v1] Add DBState to pg_control_system function

Add DBState as a column to the pg_control_system function which
would help know the database state, especially during PITR/archive
recovery. During archive recovery, the server can open up for
read-only connections even before the archive recovery finishes.
Having, pg_control_system emit database state would help the
users/service layers know it and so they can take some actions
based on it.
---
 doc/src/sgml/func.sgml                  |  5 +++++
 src/backend/utils/misc/pg_controldata.c | 11 +++++++---
 src/bin/pg_controldata/pg_controldata.c | 26 +----------------------
 src/common/controldata_utils.c          | 28 +++++++++++++++++++++++++
 src/include/catalog/pg_proc.dat         |  6 +++---
 src/include/common/controldata_utils.h  |  1 +
 6 files changed, 46 insertions(+), 31 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 8754f2f89b..0d2bd44f49 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -25166,6 +25166,11 @@ SELECT collation for ('foo' COLLATE "de_DE");
        <entry><type>timestamp with time zone</type></entry>
       </row>
 
+      <row>
+       <entry><structfield>database_cluster_state</structfield></entry>
+       <entry><type>text</type></entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/src/backend/utils/misc/pg_controldata.c b/src/backend/utils/misc/pg_controldata.c
index 781f8b8758..09bda4b9d6 100644
--- a/src/backend/utils/misc/pg_controldata.c
+++ b/src/backend/utils/misc/pg_controldata.c
@@ -31,8 +31,8 @@
 Datum
 pg_control_system(PG_FUNCTION_ARGS)
 {
-	Datum		values[4];
-	bool		nulls[4];
+	Datum		values[5];
+	bool		nulls[5];
 	TupleDesc	tupdesc;
 	HeapTuple	htup;
 	ControlFileData *ControlFile;
@@ -42,7 +42,7 @@ pg_control_system(PG_FUNCTION_ARGS)
 	 * Construct a tuple descriptor for the result row.  This must match this
 	 * function's pg_proc entry!
 	 */
-	tupdesc = CreateTemplateTupleDesc(4);
+	tupdesc = CreateTemplateTupleDesc(5);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "pg_control_version",
 					   INT4OID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "catalog_version_no",
@@ -51,6 +51,8 @@ pg_control_system(PG_FUNCTION_ARGS)
 					   INT8OID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "pg_control_last_modified",
 					   TIMESTAMPTZOID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "database_cluster_state",
+					   TEXTOID, -1, 0);
 	tupdesc = BlessTupleDesc(tupdesc);
 
 	/* read the control file */
@@ -71,6 +73,9 @@ pg_control_system(PG_FUNCTION_ARGS)
 	values[3] = TimestampTzGetDatum(time_t_to_timestamptz(ControlFile->time));
 	nulls[3] = false;
 
+	values[4] = CStringGetTextDatum(get_dbstate(ControlFile->state));
+	nulls[4] = false;
+
 	htup = heap_form_tuple(tupdesc, values, nulls);
 
 	PG_RETURN_DATUM(HeapTupleGetDatum(htup));
diff --git a/src/bin/pg_controldata/pg_controldata.c b/src/bin/pg_controldata/pg_controldata.c
index f911f98d94..1d20843391 100644
--- a/src/bin/pg_controldata/pg_controldata.c
+++ b/src/bin/pg_controldata/pg_controldata.c
@@ -45,30 +45,6 @@ usage(const char *progname)
 	printf(_("%s home page: <%s>\n"), PACKAGE_NAME, PACKAGE_URL);
 }
 
-
-static const char *
-dbState(DBState state)
-{
-	switch (state)
-	{
-		case DB_STARTUP:
-			return _("starting up");
-		case DB_SHUTDOWNED:
-			return _("shut down");
-		case DB_SHUTDOWNED_IN_RECOVERY:
-			return _("shut down in recovery");
-		case DB_SHUTDOWNING:
-			return _("shutting down");
-		case DB_IN_CRASH_RECOVERY:
-			return _("in crash recovery");
-		case DB_IN_ARCHIVE_RECOVERY:
-			return _("in archive recovery");
-		case DB_IN_PRODUCTION:
-			return _("in production");
-	}
-	return _("unrecognized status code");
-}
-
 static const char *
 wal_level_str(WalLevel wal_level)
 {
@@ -232,7 +208,7 @@ main(int argc, char *argv[])
 	printf(_("Database system identifier:           %llu\n"),
 		   (unsigned long long) ControlFile->system_identifier);
 	printf(_("Database cluster state:               %s\n"),
-		   dbState(ControlFile->state));
+		   get_dbstate(ControlFile->state));
 	printf(_("pg_control last modified:             %s\n"),
 		   pgctime_str);
 	printf(_("Latest checkpoint location:           %X/%X\n"),
diff --git a/src/common/controldata_utils.c b/src/common/controldata_utils.c
index 348f046a44..b51b693965 100644
--- a/src/common/controldata_utils.c
+++ b/src/common/controldata_utils.c
@@ -265,3 +265,31 @@ update_controlfile(const char *DataDir,
 #endif
 	}
 }
+
+/*
+ * get_dbstate()
+ *
+ * Get the database cluster state.
+ */
+const char *
+get_dbstate(DBState state)
+{
+	switch (state)
+	{
+		case DB_STARTUP:
+			return _("starting up");
+		case DB_SHUTDOWNED:
+			return _("shut down");
+		case DB_SHUTDOWNED_IN_RECOVERY:
+			return _("shut down in recovery");
+		case DB_SHUTDOWNING:
+			return _("shutting down");
+		case DB_IN_CRASH_RECOVERY:
+			return _("in crash recovery");
+		case DB_IN_ARCHIVE_RECOVERY:
+			return _("in archive recovery");
+		case DB_IN_PRODUCTION:
+			return _("in production");
+	}
+	return _("unrecognized status code");
+}
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 7024dbe10a..159421ce0e 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -11561,9 +11561,9 @@
 { oid => '3441',
   descr => 'pg_controldata general state information as a function',
   proname => 'pg_control_system', provolatile => 'v', prorettype => 'record',
-  proargtypes => '', proallargtypes => '{int4,int4,int8,timestamptz}',
-  proargmodes => '{o,o,o,o}',
-  proargnames => '{pg_control_version,catalog_version_no,system_identifier,pg_control_last_modified}',
+  proargtypes => '', proallargtypes => '{int4,int4,int8,timestamptz,text}',
+  proargmodes => '{o,o,o,o,o}',
+  proargnames => '{pg_control_version,catalog_version_no,system_identifier,pg_control_last_modified,database_cluster_state}',
   prosrc => 'pg_control_system' },
 
 { oid => '3442',
diff --git a/src/include/common/controldata_utils.h b/src/include/common/controldata_utils.h
index b1dab7547c..1ac0147724 100644
--- a/src/include/common/controldata_utils.h
+++ b/src/include/common/controldata_utils.h
@@ -15,5 +15,6 @@
 extern ControlFileData *get_controlfile(const char *DataDir, bool *crc_ok_p);
 extern void update_controlfile(const char *DataDir,
 							   ControlFileData *ControlFile, bool do_sync);
+extern const char *get_dbstate(DBState state);
 
 #endif							/* COMMON_CONTROLDATA_UTILS_H */
-- 
2.25.1