Statement-level rollback

From 5201b4686c47ac37f53debe4ed3851d4ebc224b6 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Fri, 7 Dec 2018 15:50:45 -0300
Subject: [PATCH 1/2] Support statement-level rollback

---
 doc/src/sgml/ref/begin.sgml                |   5 +-
 doc/src/sgml/ref/set_transaction.sgml      |  22 +++++-
 src/backend/access/transam/xact.c          | 120 ++++++++++++++++++++++++++---
 src/backend/commands/variable.c            |  31 ++++++++
 src/backend/parser/gram.y                  |  12 ++-
 src/backend/tcop/utility.c                 |   4 +
 src/backend/utils/misc/guc.c               |  20 +++++
 src/include/access/xact.h                  |  11 +++
 src/include/commands/variable.h            |   1 +
 src/include/parser/kwlist.h                |   1 +
 src/test/regress/expected/transactions.out |  70 +++++++++++++++++
 src/test/regress/sql/transactions.sql      |  46 +++++++++++
 12 files changed, 328 insertions(+), 15 deletions(-)

diff --git a/doc/src/sgml/ref/begin.sgml b/doc/src/sgml/ref/begin.sgml
index c23bbfb4e7..a60a3abae3 100644
--- a/doc/src/sgml/ref/begin.sgml
+++ b/doc/src/sgml/ref/begin.sgml
@@ -26,6 +26,7 @@ BEGIN [ WORK | TRANSACTION ] [ <replaceable class="parameter">transaction_mode</
 <phrase>where <replaceable class="parameter">transaction_mode</replaceable> is one of:</phrase>
 
     ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
+    ROLLBACK SCOPE TRANSACTION
     READ WRITE | READ ONLY
     [ NOT ] DEFERRABLE
 </synopsis>
@@ -58,8 +59,8 @@ BEGIN [ WORK | TRANSACTION ] [ <replaceable class="parameter">transaction_mode</
   </para>
 
   <para>
-   If the isolation level, read/write mode, or deferrable mode is specified, the new
-   transaction has those characteristics, as if
+   If the isolation level, read/write mode, rollback scope, or deferrable mode
+   is specified, the new transaction has those characteristics, as if
    <xref linkend="sql-set-transaction"/>
    was executed.
   </para>
diff --git a/doc/src/sgml/ref/set_transaction.sgml b/doc/src/sgml/ref/set_transaction.sgml
index 43b1c6c892..e6aa4f46f6 100644
--- a/doc/src/sgml/ref/set_transaction.sgml
+++ b/doc/src/sgml/ref/set_transaction.sgml
@@ -10,6 +10,11 @@
  </indexterm>
 
  <indexterm>
+  <primary>transaction rollback scope</primary>
+  <secondary>setting</secondary>
+ </indexterm>
+
+ <indexterm>
   <primary>read-only transaction</primary>
   <secondary>setting</secondary>
  </indexterm>
@@ -39,6 +44,7 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
 <phrase>where <replaceable class="parameter">transaction_mode</replaceable> is one of:</phrase>
 
     ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
+    ROLLBACK SCOPE TRANSACTION
     READ WRITE | READ ONLY
     [ NOT ] DEFERRABLE
 </synopsis>
@@ -59,7 +65,8 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
 
   <para>
    The available transaction characteristics are the transaction
-   isolation level, the transaction access mode (read/write or
+   isolation level, the rollback scope,
+   the transaction access mode (read/write or
    read-only), and the deferrable mode.
    In addition, a snapshot can be selected, though only for the current
    transaction, not as a session default.
@@ -124,6 +131,19 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
   </para>
 
   <para>
+   The rollback scope of a transaction determines the range of operations
+   which roll back when an SQL statement fails.  The default value is
+   <literal>TRANSACTION</literal>, which causes the entire transaction or
+   current subtransaction to be rolled back.  This is the only mode that can
+   be selected with <command>SET TRANSACTION</command>.  The other possible
+   mode, <literal>STATEMENT</literal>, can only be specified during connection
+   establishment, <literal>ALTER USER</literal> or <literal>ALTER DATABASE</literal>;
+   in that mode, only the failed <acronym>SQL</acronym> statement is
+   rolled back, and the transaction is automatically put back in normal
+   mode.
+  </para>
+
+  <para>
    The transaction access mode determines whether the transaction is
    read/write or read-only.  Read/write is the default.  When a
    transaction is read-only, the following SQL commands are
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index d967400384..c6fd975b7b 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -73,6 +73,8 @@
 int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
 int			XactIsoLevel;
 
+int			XactRollbackScope = XACT_ROLLBACK_SCOPE_XACT;
+
 bool		DefaultXactReadOnly = false;
 bool		XactReadOnly;
 
@@ -176,6 +178,7 @@ typedef struct TransactionStateData
 	int			savepointLevel; /* savepoint level */
 	TransState	state;			/* low-level state */
 	TBlockState blockState;		/* high-level state */
+	XactRollbackScopeValues rollbackScope;	/* automatic abort behavior */
 	int			nestingLevel;	/* transaction nesting depth */
 	int			gucNestLevel;	/* GUC context nesting depth */
 	MemoryContext curTransactionContext;	/* my xact-lifetime context */
@@ -202,6 +205,7 @@ typedef TransactionStateData *TransactionState;
 static TransactionStateData TopTransactionStateData = {
 	.state = TRANS_DEFAULT,
 	.blockState = TBLOCK_DEFAULT,
+	.rollbackScope = XACT_ROLLBACK_SCOPE_XACT,
 };
 
 /*
@@ -1820,6 +1824,8 @@ StartTransaction(void)
 	 */
 	s->state = TRANS_START;
 	s->transactionId = InvalidTransactionId;	/* until assigned */
+	/* fixed later in CommitTransactionCommand: */
+	s->rollbackScope = XACT_ROLLBACK_SCOPE_XACT;
 
 	/*
 	 * initialize current transaction state fields
@@ -2705,6 +2711,7 @@ StartTransactionCommand(void)
 			 */
 		case TBLOCK_DEFAULT:
 			StartTransaction();
+			s = CurrentTransactionState;
 			s->blockState = TBLOCK_STARTED;
 			break;
 
@@ -2717,7 +2724,23 @@ StartTransactionCommand(void)
 			 */
 		case TBLOCK_INPROGRESS:
 		case TBLOCK_IMPLICIT_INPROGRESS:
+			break;
+
+			/*
+			 * Same as above in transaction rollback scope; but in statement
+			 * rollback scope, release the previous subtransaction and create
+			 * a new one.
+			 */
 		case TBLOCK_SUBINPROGRESS:
+			if (s->rollbackScope == XACT_ROLLBACK_SCOPE_STMT)
+			{
+				CommitSubTransaction();		/* what if there's an intervening subxact? */
+				PushTransaction();
+				s = CurrentTransactionState;
+				s->name = MemoryContextStrdup(TopTransactionContext, "pg internal");
+				StartSubTransaction();
+				s->blockState = TBLOCK_SUBINPROGRESS;
+			}
 			break;
 
 			/*
@@ -2792,13 +2815,25 @@ CommitTransactionCommand(void)
 			break;
 
 			/*
-			 * We are completing a "BEGIN TRANSACTION" command, so we change
-			 * to the "transaction block in progress" state and return.  (We
-			 * assume the BEGIN did nothing to the database, so we need no
-			 * CommandCounterIncrement.)
+			 * While completing a BEGIN transaction command, we mind the
+			 * prevailing transaction rollback scope.  In the normal case of
+			 * rolling back the entire transaction, just change to the
+			 * "transaction block in progress" state and return.  (We assume
+			 * the BEGIN did nothing to the database, so we need no
+			 * CommandCounterIncrement.)  If the rollback scope is statement,
+			 * however, here we start a subtransaction to serve it.
 			 */
 		case TBLOCK_BEGIN:
+			s->rollbackScope = XactRollbackScope;
 			s->blockState = TBLOCK_INPROGRESS;
+			if (s->rollbackScope == XACT_ROLLBACK_SCOPE_STMT)
+			{
+				PushTransaction();
+				s = CurrentTransactionState;	/* changed by push */
+				s->name = MemoryContextStrdup(TopTransactionContext, "pg internal");
+				StartSubTransaction();
+				s->blockState = TBLOCK_SUBINPROGRESS;
+			}
 			break;
 
 			/*
@@ -2985,6 +3020,7 @@ CommitTransactionCommand(void)
 				savepointLevel = s->savepointLevel;
 
 				CleanupSubTransaction();
+				s = CurrentTransactionState;
 
 				DefineSavepoint(NULL);
 				s = CurrentTransactionState;	/* changed by push */
@@ -3063,6 +3099,7 @@ AbortCurrentTransaction(void)
 			 */
 		case TBLOCK_INPROGRESS:
 		case TBLOCK_PARALLEL_INPROGRESS:
+			Assert(s->rollbackScope != XACT_ROLLBACK_SCOPE_STMT);
 			AbortTransaction();
 			s->blockState = TBLOCK_ABORT;
 			/* CleanupTransaction happens when we exit TBLOCK_ABORT_END */
@@ -3120,13 +3157,32 @@ AbortCurrentTransaction(void)
 			break;
 
 			/*
-			 * We got an error inside a subtransaction.  Abort just the
-			 * subtransaction, and go to the persistent SUBABORT state until
-			 * we get ROLLBACK.
+			 * We got an error inside a subtransaction.  In transaction-
+			 * rollback-scope mode, abort just the subtransaction, and go to
+			 * the persistent SUBABORT state until we get ROLLBACK; in
+			 * statement rollback-scope mode, abort and cleanup the current
+			 * subtransaction and automatically start a new one.
 			 */
 		case TBLOCK_SUBINPROGRESS:
 			AbortSubTransaction();
-			s->blockState = TBLOCK_SUBABORT;
+
+			if (s->rollbackScope == XACT_ROLLBACK_SCOPE_STMT)
+			{
+				char   *name = s->name;
+
+				s->name = NULL;
+				CleanupSubTransaction();
+
+				PushTransaction();
+				s = CurrentTransactionState;	/* changed by push */
+				s->name = name;
+
+				AssertState(s->blockState == TBLOCK_SUBBEGIN);
+				StartSubTransaction();
+				s->blockState = TBLOCK_SUBINPROGRESS;
+			}
+			else
+				s->blockState = TBLOCK_SUBABORT;
 			break;
 
 			/*
@@ -3863,9 +3919,8 @@ DefineSavepoint(const char *name)
 
 	switch (s->blockState)
 	{
-		case TBLOCK_INPROGRESS:
-		case TBLOCK_SUBINPROGRESS:
 			/* Normal subtransaction start */
+		case TBLOCK_INPROGRESS:
 			PushTransaction();
 			s = CurrentTransactionState;	/* changed by push */
 
@@ -3878,6 +3933,50 @@ DefineSavepoint(const char *name)
 			break;
 
 			/*
+			 * As above, with a subtransaction already in progress.
+			 *
+			 * In transaction-scope rollback, we want the user-defined
+			 * savepoint to appear *before* the automatic subtransaction.
+			 * Close the one we opened above, then open and start the user
+			 * invoked one, then start a new automatic savepoint, which is
+			 * the one that CommitTransactionCommand will act upon.
+			 *
+			 * In normal mode, act just like the INPROGRESS case.
+			 */
+		case TBLOCK_SUBINPROGRESS:
+			if (s->rollbackScope == XACT_ROLLBACK_SCOPE_STMT)
+			{
+				CommitSubTransaction();
+				PushTransaction();
+				s = CurrentTransactionState;	/* changed by push */
+				if (name)
+					s->name = MemoryContextStrdup(TopTransactionContext, name);
+				StartSubTransaction();
+				s->blockState = TBLOCK_SUBINPROGRESS;
+
+				/* same as StartTransactionCommand for SUBINPROGRESS */
+				PushTransaction();
+				s = CurrentTransactionState;
+				s->name = MemoryContextStrdup(TopTransactionContext, "pg internal");
+				StartSubTransaction();
+				s->blockState = TBLOCK_SUBINPROGRESS;
+
+			}
+			else
+			{
+				PushTransaction();
+				s = CurrentTransactionState;	/* changed by push */
+
+				/*
+				 * Savepoint names, like the TransactionState block itself, live
+				 * in TopTransactionContext.
+				 */
+				if (name)
+					s->name = MemoryContextStrdup(TopTransactionContext, name);
+			}
+			break;
+
+			/*
 			 * We disallow savepoint commands in implicit transaction blocks.
 			 * There would be no great difficulty in allowing them so far as
 			 * this module is concerned, but a savepoint seems inconsistent
@@ -4547,6 +4646,7 @@ StartSubTransaction(void)
 			 TransStateAsString(s->state));
 
 	s->state = TRANS_START;
+	s->rollbackScope = s->parent->rollbackScope;
 
 	/*
 	 * Initialize subsystems for new subtransaction
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index c7e5a9ca9f..c2af9b9795 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -555,6 +555,37 @@ check_XactIsoLevel(int *newval, void **extra, GucSource source)
 }
 
 /*
+ * SET TRANSACTION ROLLBACK SCOPE
+ */
+bool
+check_XactRollbackScope(int *newval, void **extra, GucSource source)
+{
+	/* idempotent changes are okay */
+	if (*newval == XactRollbackScope)
+		return true;
+
+	/*
+	 * if in statement mode, allow downgrade to transaction mode (no going
+	 * back from this one!)
+	 */
+	if ((*newval == XACT_ROLLBACK_SCOPE_XACT) &&
+		(XactRollbackScope == XACT_ROLLBACK_SCOPE_STMT))
+		return true;
+
+	/*
+	 * We want to reject the variable unless it comes from ALTER
+	 * USER/DATABASE or connection establishment.  We don't want to
+	 * accept it in postgresql.conf or in manual SET.
+	 */
+	if (source < PGC_S_SESSION && source > PGC_S_GLOBAL)
+		return true;
+
+	GUC_check_errmsg("the transaction rollback scope cannot be changed at this level");
+	GUC_check_errhint("You may set it in PGOPTIONS or via ALTER USER/DATABASE SET.");
+	return false;
+}
+
+/*
  * SET TRANSACTION [NOT] DEFERRABLE
  */
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 2c2208ffb7..1f924101fb 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -353,7 +353,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <node>	RowSecurityOptionalWithCheck RowSecurityOptionalExpr
 %type <list>	RowSecurityDefaultToRole RowSecurityOptionalToRole
 
-%type <str>		iso_level opt_encoding
+%type <str>		iso_level rollback_scope opt_encoding
 %type <rolespec> grantee
 %type <list>	grantee_list
 %type <accesspriv> privilege
@@ -673,7 +673,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
-	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
+	SAVEPOINT SCHEMA SCHEMAS SCOPE SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
 	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STRICT_P STRIP_P
@@ -1578,6 +1578,10 @@ iso_level:	READ UNCOMMITTED						{ $$ = "read uncommitted"; }
 			| SERIALIZABLE							{ $$ = "serializable"; }
 		;
 
+rollback_scope:	TRANSACTION						{ $$ = "transaction"; }
+			| STATEMENT							{ $$ = "statement"; }
+		;
+
 opt_boolean_or_string:
 			TRUE_P									{ $$ = "true"; }
 			| FALSE_P								{ $$ = "false"; }
@@ -9916,6 +9920,9 @@ transaction_mode_item:
 			ISOLATION LEVEL iso_level
 					{ $$ = makeDefElem("transaction_isolation",
 									   makeStringConst($3, @3), @1); }
+			| ROLLBACK SCOPE rollback_scope
+					{ $$ = makeDefElem("transaction_rollback_scope",
+									   makeStringConst($3, @3), @1); }
 			| READ ONLY
 					{ $$ = makeDefElem("transaction_read_only",
 									   makeIntConst(true, @1), @1); }
@@ -15184,6 +15191,7 @@ unreserved_keyword:
 			| SAVEPOINT
 			| SCHEMA
 			| SCHEMAS
+			| SCOPE
 			| SCROLL
 			| SEARCH
 			| SECOND_P
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 970c94ee80..3077a9adb5 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -427,6 +427,10 @@ standard_ProcessUtility(PlannedStmt *pstmt,
 									SetPGVariable("transaction_isolation",
 												  list_make1(item->arg),
 												  true);
+								if (strcmp(item->defname, "transaction_rollback_scope") == 0)
+									SetPGVariable("transaction_rollback_scope",
+												  list_make1(item->arg),
+												  true);
 								else if (strcmp(item->defname, "transaction_read_only") == 0)
 									SetPGVariable("transaction_read_only",
 												  list_make1(item->arg),
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6fe1939881..de614d5e05 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -295,6 +295,12 @@ static const struct config_enum_entry isolation_level_options[] = {
 	{NULL, 0}
 };
 
+static const struct config_enum_entry rollback_scope_options[] = {
+	{"transaction", XACT_ROLLBACK_SCOPE_XACT, false},
+	{"statement", XACT_ROLLBACK_SCOPE_STMT, false},
+	{NULL, 0}
+};
+
 static const struct config_enum_entry session_replication_role_options[] = {
 	{"origin", SESSION_REPLICATION_ROLE_ORIGIN, false},
 	{"replica", SESSION_REPLICATION_ROLE_REPLICA, false},
@@ -4151,6 +4157,17 @@ static struct config_enum ConfigureNamesEnum[] =
 	},
 
 	{
+		{"transaction_rollback_scope", PGC_USERSET, CLIENT_CONN_STATEMENT,
+			gettext_noop("Sets the scope of rollback when the current transaction aborts."),
+			NULL,
+			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+		},
+		&XactRollbackScope,
+		XACT_ROLLBACK_SCOPE_XACT, rollback_scope_options,
+		check_XactRollbackScope, NULL, NULL
+	},
+
+	{
 		{"IntervalStyle", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the display format for interval values."),
 			NULL,
@@ -7853,6 +7870,9 @@ ExecSetVariableStmt(VariableSetStmt *stmt, bool isTopLevel)
 					else if (strcmp(item->defname, "transaction_read_only") == 0)
 						SetPGVariable("transaction_read_only",
 									  list_make1(item->arg), stmt->is_local);
+					else if (strcmp(item->defname, "transaction_rollback_scope") == 0)
+						SetPGVariable("transaction_rollback_scope",
+									  list_make1(item->arg), stmt->is_local);
 					else if (strcmp(item->defname, "transaction_deferrable") == 0)
 						SetPGVariable("transaction_deferrable",
 									  list_make1(item->arg), stmt->is_local);
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index 689c57c592..dad8bb172d 100644
--- a/src/include/access/xact.h
+++ b/src/include/access/xact.h
@@ -50,6 +50,17 @@ extern PGDLLIMPORT int XactIsoLevel;
 #define IsolationUsesXactSnapshot() (XactIsoLevel >= XACT_REPEATABLE_READ)
 #define IsolationIsSerializable() (XactIsoLevel == XACT_SERIALIZABLE)
 
+/*
+ * Transaction rollback scope
+ */
+typedef enum
+{
+	XACT_ROLLBACK_SCOPE_XACT,
+	XACT_ROLLBACK_SCOPE_STMT
+} XactRollbackScopeValues;
+
+extern PGDLLIMPORT int XactRollbackScope;
+
 /* Xact read-only state */
 extern bool DefaultXactReadOnly;
 extern bool XactReadOnly;
diff --git a/src/include/commands/variable.h b/src/include/commands/variable.h
index 7373a3f99f..6239ee1788 100644
--- a/src/include/commands/variable.h
+++ b/src/include/commands/variable.h
@@ -23,6 +23,7 @@ extern void assign_log_timezone(const char *newval, void *extra);
 extern const char *show_log_timezone(void);
 extern bool check_transaction_read_only(bool *newval, void **extra, GucSource source);
 extern bool check_XactIsoLevel(int *newval, void **extra, GucSource source);
+extern bool check_XactRollbackScope(int *newval, void **extra, GucSource source);
 extern bool check_transaction_deferrable(bool *newval, void **extra, GucSource source);
 extern bool check_random_seed(double *newval, void **extra, GucSource source);
 extern void assign_random_seed(double newval, void *extra);
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 23db40147b..cd739e1149 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -353,6 +353,7 @@ PG_KEYWORD("rule", RULE, UNRESERVED_KEYWORD)
 PG_KEYWORD("savepoint", SAVEPOINT, UNRESERVED_KEYWORD)
 PG_KEYWORD("schema", SCHEMA, UNRESERVED_KEYWORD)
 PG_KEYWORD("schemas", SCHEMAS, UNRESERVED_KEYWORD)
+PG_KEYWORD("scope", SCOPE, UNRESERVED_KEYWORD)
 PG_KEYWORD("scroll", SCROLL, UNRESERVED_KEYWORD)
 PG_KEYWORD("search", SEARCH, UNRESERVED_KEYWORD)
 PG_KEYWORD("second", SECOND_P, UNRESERVED_KEYWORD)
diff --git a/src/test/regress/expected/transactions.out b/src/test/regress/expected/transactions.out
index 69e176c525..1a1a28be67 100644
--- a/src/test/regress/expected/transactions.out
+++ b/src/test/regress/expected/transactions.out
@@ -659,6 +659,76 @@ ERROR:  portal "ctt" cannot be run
 COMMIT;
 DROP FUNCTION create_temp_tab();
 DROP FUNCTION invert(x float8);
+-- tests for statement-scope rollback
+select current_user \gset
+CREATE USER regress_transactions_user;
+ALTER USER regress_transactions_user SET transaction_rollback_scope TO statement;
+\c - regress_transactions_user
+SHOW transaction_rollback_scope;
+ transaction_rollback_scope 
+----------------------------
+ statement
+(1 row)
+
+CREATE TABLE xact_rscope (a int);
+-- elementary test: three separate insertions in a transaction, an abort in the
+-- middle one.  We expect the other two to succeed.
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (0/0);
+ERROR:  division by zero
+INSERT INTO xact_rscope VALUES (2);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 2
+(2 rows)
+
+-- DO blocks don't have this behavior
+DO $$
+BEGIN
+	INSERT INTO xact_rscope VALUES (3);
+	INSERT INTO xact_rscope VALUES (4/0);
+	INSERT INTO xact_rscope VALUES (5);
+END; $$;
+ERROR:  division by zero
+CONTEXT:  SQL statement "INSERT INTO xact_rscope VALUES (4/0)"
+PL/pgSQL function inline_code_block line 4 at SQL statement
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 2
+(2 rows)
+
+-- implicit transaction blocks don't have this behavior
+INSERT INTO xact_rscope VALUES (6)\; INSERT INTO xact_rscope VALUES (7/0)\; INSERT INTO xact_rscope VALUES (8);
+ERROR:  division by zero
+-- test savepoints
+BEGIN;
+INSERT INTO xact_rscope VALUES (9);
+SAVEPOINT xact_svpt;
+INSERT INTO xact_rscope VALUES (10);
+INSERT INTO xact_rscope VALUES (11/0);
+ERROR:  division by zero
+ROLLBACK TO xact_svpt;
+INSERT INTO xact_rscope VALUES (12);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a  
+----
+  1
+  2
+  9
+ 12
+(4 rows)
+
+-- clean up
+\c - :current_user
+DROP OWNED BY regress_transactions_user;
+DROP USER regress_transactions_user;
 -- Test assorted behaviors around the implicit transaction block created
 -- when multiple SQL commands are sent in a single Query message.  These
 -- tests rely on the fact that psql will not break SQL commands apart at a
diff --git a/src/test/regress/sql/transactions.sql b/src/test/regress/sql/transactions.sql
index 2e3739fd6c..3ac3450545 100644
--- a/src/test/regress/sql/transactions.sql
+++ b/src/test/regress/sql/transactions.sql
@@ -418,6 +418,52 @@ COMMIT;
 DROP FUNCTION create_temp_tab();
 DROP FUNCTION invert(x float8);
 
+-- tests for statement-scope rollback
+select current_user \gset
+CREATE USER regress_transactions_user;
+ALTER USER regress_transactions_user SET transaction_rollback_scope TO statement;
+\c - regress_transactions_user
+SHOW transaction_rollback_scope;
+
+CREATE TABLE xact_rscope (a int);
+
+-- elementary test: three separate insertions in a transaction, an abort in the
+-- middle one.  We expect the other two to succeed.
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (0/0);
+INSERT INTO xact_rscope VALUES (2);
+COMMIT;
+SELECT * FROM xact_rscope;
+
+-- DO blocks don't have this behavior
+DO $$
+BEGIN
+	INSERT INTO xact_rscope VALUES (3);
+	INSERT INTO xact_rscope VALUES (4/0);
+	INSERT INTO xact_rscope VALUES (5);
+END; $$;
+SELECT * FROM xact_rscope;
+
+-- implicit transaction blocks don't have this behavior
+INSERT INTO xact_rscope VALUES (6)\; INSERT INTO xact_rscope VALUES (7/0)\; INSERT INTO xact_rscope VALUES (8);
+
+-- test savepoints
+BEGIN;
+INSERT INTO xact_rscope VALUES (9);
+SAVEPOINT xact_svpt;
+INSERT INTO xact_rscope VALUES (10);
+INSERT INTO xact_rscope VALUES (11/0);
+ROLLBACK TO xact_svpt;
+INSERT INTO xact_rscope VALUES (12);
+COMMIT;
+SELECT * FROM xact_rscope;
+
+-- clean up
+\c - :current_user
+DROP OWNED BY regress_transactions_user;
+DROP USER regress_transactions_user;
+
 
 -- Test assorted behaviors around the implicit transaction block created
 -- when multiple SQL commands are sent in a single Query message.  These
-- 
2.11.0

From 671de0c55ba20133b858933e02346327c65791a4 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Fri, 7 Dec 2018 15:57:28 -0300
Subject: [PATCH 2/2] Remove restrictions on setting rollback scope

---
 doc/src/sgml/ref/set_transaction.sgml      |  11 +-
 src/backend/access/transam/xact.c          |  39 ++++++-
 src/backend/commands/variable.c            |  31 ------
 src/backend/utils/misc/guc.c               |   2 +-
 src/include/commands/variable.h            |   4 +-
 src/test/regress/expected/transactions.out | 170 +++++++++++++++++++++++++++++
 src/test/regress/sql/transactions.sql      |  95 ++++++++++++++++
 7 files changed, 311 insertions(+), 41 deletions(-)

diff --git a/doc/src/sgml/ref/set_transaction.sgml b/doc/src/sgml/ref/set_transaction.sgml
index e6aa4f46f6..ef94e57ef6 100644
--- a/doc/src/sgml/ref/set_transaction.sgml
+++ b/doc/src/sgml/ref/set_transaction.sgml
@@ -134,13 +134,10 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
    The rollback scope of a transaction determines the range of operations
    which roll back when an SQL statement fails.  The default value is
    <literal>TRANSACTION</literal>, which causes the entire transaction or
-   current subtransaction to be rolled back.  This is the only mode that can
-   be selected with <command>SET TRANSACTION</command>.  The other possible
-   mode, <literal>STATEMENT</literal>, can only be specified during connection
-   establishment, <literal>ALTER USER</literal> or <literal>ALTER DATABASE</literal>;
-   in that mode, only the failed <acronym>SQL</acronym> statement is
-   rolled back, and the transaction is automatically put back in normal
-   mode.
+   current subtransaction to be rolled back.  The other possible mode is
+   <literal>STATEMENT</literal>, in which only the failed
+   <acronym>SQL</acronym> statement is rolled back, and the transaction
+   is automatically put back in normal mode.
   </para>
 
   <para>
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index c6fd975b7b..b30683eb9f 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -36,6 +36,7 @@
 #include "commands/async.h"
 #include "commands/tablecmds.h"
 #include "commands/trigger.h"
+#include "commands/variable.h"
 #include "executor/spi.h"
 #include "libpq/be-fsstubs.h"
 #include "libpq/pqsignal.h"
@@ -2722,10 +2723,26 @@ StartTransactionCommand(void)
 			 * that any needed CommandCounterIncrement was done by the
 			 * previous CommitTransactionCommand.)
 			 */
-		case TBLOCK_INPROGRESS:
 		case TBLOCK_IMPLICIT_INPROGRESS:
 			break;
 
+			/* Normally there's nothing to do for the in-progress case.  But in
+			 * statement-scoped rollback mode, we start a new subtransaction
+			 * here to which we can roll back.  This case is pretty rare: it
+			 * only occurs when the GUC is changed partway through a
+			 * transaction.
+			 */
+		case TBLOCK_INPROGRESS:
+			if (s->rollbackScope == XACT_ROLLBACK_SCOPE_STMT)
+			{
+				PushTransaction();
+				s = CurrentTransactionState;
+				s->name = MemoryContextStrdup(TopTransactionContext, "pg internal");
+				StartSubTransaction();
+				s->blockState = TBLOCK_SUBINPROGRESS;
+			}
+			break;
+
 			/*
 			 * Same as above in transaction rollback scope; but in statement
 			 * rollback scope, release the previous subtransaction and create
@@ -5243,6 +5260,26 @@ ShowTransactionStateRec(const char *str, TransactionState s)
 }
 
 /*
+ * GUC assign hook for SET TRANSACTION ROLLBACK SCOPE
+ */
+void
+assign_XactRollbackScope(int newval, void *extra)
+{
+	TransactionState s = CurrentTransactionState;
+
+	/*
+	 * Alter the GUC setting for future transactions ...
+	 */
+	XactRollbackScope = newval;
+
+	/* ... as well as update the current transaction's status */
+	if ((s->state == TRANS_INPROGRESS) && (newval != s->rollbackScope))
+		s->rollbackScope = newval;
+
+	/* Should we prepare transaction state here? */
+}
+
+/*
  * BlockStateAsString
  *		Debug support
  */
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index c2af9b9795..c7e5a9ca9f 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -555,37 +555,6 @@ check_XactIsoLevel(int *newval, void **extra, GucSource source)
 }
 
 /*
- * SET TRANSACTION ROLLBACK SCOPE
- */
-bool
-check_XactRollbackScope(int *newval, void **extra, GucSource source)
-{
-	/* idempotent changes are okay */
-	if (*newval == XactRollbackScope)
-		return true;
-
-	/*
-	 * if in statement mode, allow downgrade to transaction mode (no going
-	 * back from this one!)
-	 */
-	if ((*newval == XACT_ROLLBACK_SCOPE_XACT) &&
-		(XactRollbackScope == XACT_ROLLBACK_SCOPE_STMT))
-		return true;
-
-	/*
-	 * We want to reject the variable unless it comes from ALTER
-	 * USER/DATABASE or connection establishment.  We don't want to
-	 * accept it in postgresql.conf or in manual SET.
-	 */
-	if (source < PGC_S_SESSION && source > PGC_S_GLOBAL)
-		return true;
-
-	GUC_check_errmsg("the transaction rollback scope cannot be changed at this level");
-	GUC_check_errhint("You may set it in PGOPTIONS or via ALTER USER/DATABASE SET.");
-	return false;
-}
-
-/*
  * SET TRANSACTION [NOT] DEFERRABLE
  */
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index de614d5e05..a8da9decf9 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -4164,7 +4164,7 @@ static struct config_enum ConfigureNamesEnum[] =
 		},
 		&XactRollbackScope,
 		XACT_ROLLBACK_SCOPE_XACT, rollback_scope_options,
-		check_XactRollbackScope, NULL, NULL
+		NULL, assign_XactRollbackScope, NULL
 	},
 
 	{
diff --git a/src/include/commands/variable.h b/src/include/commands/variable.h
index 6239ee1788..9cd8131e5b 100644
--- a/src/include/commands/variable.h
+++ b/src/include/commands/variable.h
@@ -23,7 +23,6 @@ extern void assign_log_timezone(const char *newval, void *extra);
 extern const char *show_log_timezone(void);
 extern bool check_transaction_read_only(bool *newval, void **extra, GucSource source);
 extern bool check_XactIsoLevel(int *newval, void **extra, GucSource source);
-extern bool check_XactRollbackScope(int *newval, void **extra, GucSource source);
 extern bool check_transaction_deferrable(bool *newval, void **extra, GucSource source);
 extern bool check_random_seed(double *newval, void **extra, GucSource source);
 extern void assign_random_seed(double newval, void *extra);
@@ -36,4 +35,7 @@ extern bool check_role(char **newval, void **extra, GucSource source);
 extern void assign_role(const char *newval, void *extra);
 extern const char *show_role(void);
 
+/* in xact.c */
+extern void assign_XactRollbackScope(int newval, void *extra);
+
 #endif							/* VARIABLE_H */
diff --git a/src/test/regress/expected/transactions.out b/src/test/regress/expected/transactions.out
index 1a1a28be67..a259cd6121 100644
--- a/src/test/regress/expected/transactions.out
+++ b/src/test/regress/expected/transactions.out
@@ -725,10 +725,180 @@ SELECT * FROM xact_rscope;
  12
 (4 rows)
 
+-- test changing rollback scope to 'transaction' partway through
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+SHOW transaction_rollback_scope;
+ transaction_rollback_scope 
+----------------------------
+ statement
+(1 row)
+
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (2/0);
+ERROR:  division by zero
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (3);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 3
+(2 rows)
+
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (2/0);
+ERROR:  division by zero
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (3);
+INSERT INTO xact_rscope VALUES (4/0);
+ERROR:  division by zero
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+(0 rows)
+
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (2/0);
+ERROR:  division by zero
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (4/0);
+ERROR:  division by zero
+ROLLBACK TO foo;
+INSERT INTO xact_rscope VALUES (5);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 5
+(2 rows)
+
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (2/0);
+ERROR:  division by zero
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (4);
+RELEASE SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (5);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 4
+ 5
+(3 rows)
+
 -- clean up
 \c - :current_user
 DROP OWNED BY regress_transactions_user;
 DROP USER regress_transactions_user;
+-- We allow the GUC to be changed mid-session too
+CREATE TABLE xact_rscope (a int);
+SHOW transaction_rollback_scope;
+ transaction_rollback_scope 
+----------------------------
+ transaction
+(1 row)
+
+BEGIN TRANSACTION ROLLBACK SCOPE STATEMENT;
+SHOW transaction_rollback_scope;
+ transaction_rollback_scope 
+----------------------------
+ statement
+(1 row)
+
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (2/0);
+ERROR:  division by zero
+INSERT INTO xact_rscope VALUES (3), (4/0);
+ERROR:  division by zero
+INSERT INTO xact_rscope VALUES (5);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 5
+(2 rows)
+
+TRUNCATE TABLE xact_rscope;
+SET transaction_rollback_scope TO 'statement';
+BEGIN;
+INSERT INTO xact_rscope VALUES (5);
+INSERT INTO xact_rscope VALUES (6/0);
+ERROR:  division by zero
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 5
+(1 row)
+
+RESET transaction_rollback_scope;
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+SHOW transaction_rollback_scope;
+ transaction_rollback_scope 
+----------------------------
+ transaction
+(1 row)
+
+INSERT INTO xact_rscope VALUES (1);
+SET LOCAL transaction_rollback_scope TO 'statement';
+INSERT INTO xact_rscope VALUES (2/0);
+ERROR:  division by zero
+INSERT INTO xact_rscope VALUES (3);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 3
+(2 rows)
+
+SHOW transaction_rollback_scope;
+ transaction_rollback_scope 
+----------------------------
+ transaction
+(1 row)
+
+TRUNCATE TABLE xact_rscope;
+BEGIN ROLLBACK SCOPE STATEMENT;
+INSERT INTO xact_rscope VALUES (1);
+SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (2/0);
+ERROR:  division by zero
+INSERT INTO xact_rscope VALUES (3);
+RELEASE SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (4);
+SAVEPOINT bar;
+INSERT INTO xact_rscope VALUES (5);
+INSERT INTO xact_rscope VALUES (6/0);
+ERROR:  division by zero
+ROLLBACK TO bar;
+INSERT INTO xact_rscope VALUES (7);
+COMMIT;
+SELECT * FROM xact_rscope;
+ a 
+---
+ 1
+ 3
+ 4
+ 7
+(4 rows)
+
 -- Test assorted behaviors around the implicit transaction block created
 -- when multiple SQL commands are sent in a single Query message.  These
 -- tests rely on the fact that psql will not break SQL commands apart at a
diff --git a/src/test/regress/sql/transactions.sql b/src/test/regress/sql/transactions.sql
index 3ac3450545..4fa8246de7 100644
--- a/src/test/regress/sql/transactions.sql
+++ b/src/test/regress/sql/transactions.sql
@@ -459,11 +459,106 @@ INSERT INTO xact_rscope VALUES (12);
 COMMIT;
 SELECT * FROM xact_rscope;
 
+-- test changing rollback scope to 'transaction' partway through
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+SHOW transaction_rollback_scope;
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (2/0);
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (3);
+COMMIT;
+SELECT * FROM xact_rscope;
+
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (2/0);
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (3);
+INSERT INTO xact_rscope VALUES (4/0);
+COMMIT;
+SELECT * FROM xact_rscope;
+
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (2/0);
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (4/0);
+ROLLBACK TO foo;
+INSERT INTO xact_rscope VALUES (5);
+COMMIT;
+SELECT * FROM xact_rscope;
+
+
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+INSERT INTO xact_rscope VALUES (1);
+SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (2/0);
+SET LOCAL transaction_rollback_scope TO 'transaction';
+INSERT INTO xact_rscope VALUES (4);
+RELEASE SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (5);
+COMMIT;
+SELECT * FROM xact_rscope;
+
 -- clean up
 \c - :current_user
 DROP OWNED BY regress_transactions_user;
 DROP USER regress_transactions_user;
 
+-- We allow the GUC to be changed mid-session too
+CREATE TABLE xact_rscope (a int);
+SHOW transaction_rollback_scope;
+BEGIN TRANSACTION ROLLBACK SCOPE STATEMENT;
+SHOW transaction_rollback_scope;
+INSERT INTO xact_rscope VALUES (1);
+INSERT INTO xact_rscope VALUES (2/0);
+INSERT INTO xact_rscope VALUES (3), (4/0);
+INSERT INTO xact_rscope VALUES (5);
+COMMIT;
+SELECT * FROM xact_rscope;
+
+TRUNCATE TABLE xact_rscope;
+SET transaction_rollback_scope TO 'statement';
+BEGIN;
+INSERT INTO xact_rscope VALUES (5);
+INSERT INTO xact_rscope VALUES (6/0);
+COMMIT;
+SELECT * FROM xact_rscope;
+RESET transaction_rollback_scope;
+
+TRUNCATE TABLE xact_rscope;
+BEGIN;
+SHOW transaction_rollback_scope;
+INSERT INTO xact_rscope VALUES (1);
+SET LOCAL transaction_rollback_scope TO 'statement';
+INSERT INTO xact_rscope VALUES (2/0);
+INSERT INTO xact_rscope VALUES (3);
+COMMIT;
+SELECT * FROM xact_rscope;
+SHOW transaction_rollback_scope;
+
+TRUNCATE TABLE xact_rscope;
+BEGIN ROLLBACK SCOPE STATEMENT;
+INSERT INTO xact_rscope VALUES (1);
+SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (2/0);
+INSERT INTO xact_rscope VALUES (3);
+RELEASE SAVEPOINT foo;
+INSERT INTO xact_rscope VALUES (4);
+SAVEPOINT bar;
+INSERT INTO xact_rscope VALUES (5);
+INSERT INTO xact_rscope VALUES (6/0);
+ROLLBACK TO bar;
+INSERT INTO xact_rscope VALUES (7);
+COMMIT;
+SELECT * FROM xact_rscope;
+
+
 
 -- Test assorted behaviors around the implicit transaction block created
 -- when multiple SQL commands are sent in a single Query message.  These
-- 
2.11.0