savepoint_commit_performance.v1.patch

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 18e9ce1..07c84b4 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -269,7 +269,7 @@ static TransactionId RecordTransactionAbort(bool isSubXact);
 static void StartTransaction(void);
 
 static void StartSubTransaction(void);
-static void CommitSubTransaction(void);
+static void CommitSubTransaction(bool isTopLevel);
 static void AbortSubTransaction(void);
 static void CleanupSubTransaction(void);
 static void PushTransaction(void);
@@ -2518,7 +2518,7 @@ CommitTransactionCommand(void)
 		case TBLOCK_SUBEND:
 			do
 			{
-				CommitSubTransaction();
+				CommitSubTransaction(true);
 				s = CurrentTransactionState;	/* changed by pop */
 			} while (s->blockState == TBLOCK_SUBEND);
 			/* If we had a COMMIT command, finish off the main xact too */
@@ -3664,7 +3664,7 @@ ReleaseCurrentSubTransaction(void)
 			 BlockStateAsString(s->blockState));
 	Assert(s->state == TRANS_INPROGRESS);
 	MemoryContextSwitchTo(CurTransactionContext);
-	CommitSubTransaction();
+	CommitSubTransaction(false);
 	s = CurrentTransactionState;	/* changed by pop */
 	Assert(s->state == TRANS_INPROGRESS);
 }
@@ -3925,9 +3925,13 @@ StartSubTransaction(void)
  *
  *	The caller has to make sure to always reassign CurrentTransactionState
  *	if it has a local pointer to it after calling this function.
+ *
+ *	isTopLevel means that this CommitSubTransaction() is being issued as a
+ *	sequence of actions leading directly to a main transaction commit
+ *	allowing some actions to be optimised.
  */
 static void
-CommitSubTransaction(void)
+CommitSubTransaction(bool isTopLevel)
 {
 	TransactionState s = CurrentTransactionState;
 
@@ -3974,15 +3978,21 @@ CommitSubTransaction(void)
 
 	/*
 	 * The only lock we actually release here is the subtransaction XID lock.
-	 * The rest just get transferred to the parent resource owner.
 	 */
 	CurrentResourceOwner = s->curTransactionOwner;
 	if (TransactionIdIsValid(s->transactionId))
 		XactLockTableDelete(s->transactionId);
 
+	/*
+	 * Other locks should get transferred to their parent resource owner.
+	 * Doing that is an O(N^2) operation, so if isTopLevel then we can just
+	 * leave the lock records as they are, knowing they will all get released
+	 * by the top level commit using ProcReleaseLocks(). We only optimize
+	 * this for commit; aborts may need to do other cleanup.
+	 */
 	ResourceOwnerRelease(s->curTransactionOwner,
 						 RESOURCE_RELEASE_LOCKS,
-						 true, false);
+						 true, isTopLevel);
 	ResourceOwnerRelease(s->curTransactionOwner,
 						 RESOURCE_RELEASE_AFTER_LOCKS,
 						 true, false);