Transaction chaining

Add command variants COMMIT AND CHAIN and ROLLBACK AND CHAIN, which
start new transactions with the same transaction characteristics as the
just finished one, per SQL standard.

Support for transaction chaining in PL/pgSQL is also added.  This
functionality is especially useful when running COMMIT in a loop in
PL/pgSQL.

Reviewed-by: Fabien COELHO <coelho@cri.ensmp.fr>
Discussion: https://www.postgresql.org/message-id/flat/28536681-324b-10dc-ade8-ab46f7645a5a@2ndquadrant.com

1 files changed, 47 insertions, 3 deletions

diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index d898f4ca78d..6e262d1a3ad 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -217,8 +217,8 @@ SPI_start_transaction(void)
 	MemoryContextSwitchTo(oldcontext);
 }
 
-void
-SPI_commit(void)
+static void
+_SPI_commit(bool chain)
 {
 	MemoryContext oldcontext = CurrentMemoryContext;
 
@@ -250,14 +250,36 @@ SPI_commit(void)
 	while (ActiveSnapshotSet())
 		PopActiveSnapshot();
 
+	if (chain)
+		SaveTransactionCharacteristics();
+
 	CommitTransactionCommand();
+
+	if (chain)
+	{
+		StartTransactionCommand();
+		RestoreTransactionCharacteristics();
+	}
+
 	MemoryContextSwitchTo(oldcontext);
 
 	_SPI_current->internal_xact = false;
 }
 
 void
-SPI_rollback(void)
+SPI_commit(void)
+{
+	_SPI_commit(false);
+}
+
+void
+SPI_commit_and_chain(void)
+{
+	_SPI_commit(true);
+}
+
+static void
+_SPI_rollback(bool chain)
 {
 	MemoryContext oldcontext = CurrentMemoryContext;
 
@@ -274,12 +296,34 @@ SPI_rollback(void)
 
 	_SPI_current->internal_xact = true;
 
+	if (chain)
+		SaveTransactionCharacteristics();
+
 	AbortCurrentTransaction();
+
+	if (chain)
+	{
+		StartTransactionCommand();
+		RestoreTransactionCharacteristics();
+	}
+
 	MemoryContextSwitchTo(oldcontext);
 
 	_SPI_current->internal_xact = false;
 }
 
+void
+SPI_rollback(void)
+{
+	_SPI_rollback(false);
+}
+
+void
+SPI_rollback_and_chain(void)
+{
+	_SPI_rollback(true);
+}
+
 /*
  * Clean up SPI state.  Called on transaction end (of non-SPI-internal
  * transactions) and when returning to the main loop on error.