Remove unnecessary PG_TRY overhead for CurrentResourceOwner changes.

resowner/README contained advice to use a PG_TRY block to restore the
old CurrentResourceOwner value anywhere that that variable is transiently
changed.  That advice was only inconsistently followed, however, and
on reflection it seems like unnecessary overhead.  We don't bother
with such a convention for transient CurrentMemoryContext changes,
on the grounds that any (sub)transaction abort will start out by
resetting CurrentMemoryContext to what it wants.  But the same is
true of CurrentResourceOwner, so there seems no need to treat it
differently.

Hence, remove PG_TRY blocks that exist only to restore CurrentResourceOwner
before re-throwing the error.  There are a couple of places that restore
it along with some other actions, and I left those alone; the restore is
probably unnecessary but no noticeable gain will result from removing it.

Discussion: https://postgr.es/m/5236.1507583529@sss.pgh.pa.us

src/backend/access/transam/xact.c

@@ -575,18 +575,10 @@ AssignTransactionId(TransactionState s)
 	 * ResourceOwner.
 	 */
 	currentOwner = CurrentResourceOwner;
-	PG_TRY();
-	{
 	CurrentResourceOwner = s->curTransactionOwner;
+
 	XactLockTableInsert(s->transactionId);
-	}
-	PG_CATCH();
-	{
-		/* Ensure CurrentResourceOwner is restored on error */
-		CurrentResourceOwner = currentOwner;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
+
 	CurrentResourceOwner = currentOwner;
 
 	/*

src/backend/commands/portalcmds.c

@@ -294,21 +294,13 @@ PortalCleanup(Portal portal)
 
 			/* We must make the portal's resource owner current */
 			saveResourceOwner = CurrentResourceOwner;
-			PG_TRY();
-			{
 			if (portal->resowner)
 				CurrentResourceOwner = portal->resowner;
+
 			ExecutorFinish(queryDesc);
 			ExecutorEnd(queryDesc);
 			FreeQueryDesc(queryDesc);
-			}
-			PG_CATCH();
-			{
-				/* Ensure CurrentResourceOwner is restored on error */
-				CurrentResourceOwner = saveResourceOwner;
-				PG_RE_THROW();
-			}
-			PG_END_TRY();
+
 			CurrentResourceOwner = saveResourceOwner;
 		}
 	}

src/backend/commands/sequence.c

@@ -1055,18 +1055,10 @@ lock_and_open_sequence(SeqTable seq)
 		ResourceOwner currentOwner;
 
 		currentOwner = CurrentResourceOwner;
-		PG_TRY();
-		{
 		CurrentResourceOwner = TopTransactionResourceOwner;
+
 		LockRelationOid(seq->relid, RowExclusiveLock);
-		}
-		PG_CATCH();
-		{
-			/* Ensure CurrentResourceOwner is restored on error */
-			CurrentResourceOwner = currentOwner;
-			PG_RE_THROW();
-		}
-		PG_END_TRY();
+
 		CurrentResourceOwner = currentOwner;
 
 		/* Flag that we have a lock in the current xact */

src/backend/commands/trigger.c

@@ -3639,17 +3639,10 @@ GetCurrentFDWTuplestore(void)
 		 */
 		oldcxt = MemoryContextSwitchTo(CurTransactionContext);
 		saveResourceOwner = CurrentResourceOwner;
-		PG_TRY();
-		{
 		CurrentResourceOwner = CurTransactionResourceOwner;
+
 		ret = tuplestore_begin_heap(false, false, work_mem);
-		}
-		PG_CATCH();
-		{
-			CurrentResourceOwner = saveResourceOwner;
-			PG_RE_THROW();
-		}
-		PG_END_TRY();
+
 		CurrentResourceOwner = saveResourceOwner;
 		MemoryContextSwitchTo(oldcxt);
 
@@ -4468,20 +4461,13 @@ MakeTransitionCaptureState(TriggerDesc *trigdesc, Oid relid, CmdType cmdType)
 	/* Now create required tuplestore(s), if we don't have them already. */
 	oldcxt = MemoryContextSwitchTo(CurTransactionContext);
 	saveResourceOwner = CurrentResourceOwner;
-	PG_TRY();
-	{
 	CurrentResourceOwner = CurTransactionResourceOwner;
+
 	if (need_old && table->old_tuplestore == NULL)
 		table->old_tuplestore = tuplestore_begin_heap(false, false, work_mem);
 	if (need_new && table->new_tuplestore == NULL)
 		table->new_tuplestore = tuplestore_begin_heap(false, false, work_mem);
-	}
-	PG_CATCH();
-	{
-		CurrentResourceOwner = saveResourceOwner;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
+
 	CurrentResourceOwner = saveResourceOwner;
 	MemoryContextSwitchTo(oldcxt);
 

src/backend/storage/large_object/inv_api.c

@@ -75,8 +75,6 @@ open_lo_relation(void)
 
 	/* Arrange for the top xact to own these relation references */
 	currentOwner = CurrentResourceOwner;
-	PG_TRY();
-	{
 	CurrentResourceOwner = TopTransactionResourceOwner;
 
 	/* Use RowExclusiveLock since we might either read or write */
@@ -84,14 +82,7 @@ open_lo_relation(void)
 		lo_heap_r = heap_open(LargeObjectRelationId, RowExclusiveLock);
 	if (lo_index_r == NULL)
 		lo_index_r = index_open(LargeObjectLOidPNIndexId, RowExclusiveLock);
-	}
-	PG_CATCH();
-	{
-		/* Ensure CurrentResourceOwner is restored on error */
-		CurrentResourceOwner = currentOwner;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
+
 	CurrentResourceOwner = currentOwner;
 }
 
@@ -112,22 +103,13 @@ close_lo_relation(bool isCommit)
 			ResourceOwner currentOwner;
 
 			currentOwner = CurrentResourceOwner;
-			PG_TRY();
-			{
 			CurrentResourceOwner = TopTransactionResourceOwner;
 
 			if (lo_index_r)
 				index_close(lo_index_r, NoLock);
 			if (lo_heap_r)
 				heap_close(lo_heap_r, NoLock);
-			}
-			PG_CATCH();
-			{
-				/* Ensure CurrentResourceOwner is restored on error */
-				CurrentResourceOwner = currentOwner;
-				PG_RE_THROW();
-			}
-			PG_END_TRY();
+
 			CurrentResourceOwner = currentOwner;
 		}
 		lo_heap_r = NULL;

src/backend/utils/resowner/README

@@ -80,7 +80,3 @@ CurrentResourceOwner must point to the same resource owner that was current
 when the buffer, lock, or cache reference was acquired.  It would be possible
 to relax this restriction given additional bookkeeping effort, but at present
 there seems no need.
-
-Code that transiently changes CurrentResourceOwner should generally use a
-PG_TRY construct to ensure that the previous value of CurrentResourceOwner
-is restored if control is lost during an error exit.

src/backend/utils/resowner/resowner.c

@@ -473,21 +473,8 @@ ResourceOwnerRelease(ResourceOwner owner,
 					 bool isCommit,
 					 bool isTopLevel)
 {
-	/* Rather than PG_TRY at every level of recursion, set it up once */
-	ResourceOwner save;
-
-	save = CurrentResourceOwner;
-	PG_TRY();
-	{
+	/* There's not currently any setup needed before recursing */
 	ResourceOwnerReleaseInternal(owner, phase, isCommit, isTopLevel);
-	}
-	PG_CATCH();
-	{
-		CurrentResourceOwner = save;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
-	CurrentResourceOwner = save;
 }
 
 static void
@@ -507,8 +494,7 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
 
 	/*
 	 * Make CurrentResourceOwner point to me, so that ReleaseBuffer etc don't
-	 * get confused.  We needn't PG_TRY here because the outermost level will
-	 * fix it on error abort.
+	 * get confused.
 	 */
 	save = CurrentResourceOwner;
 	CurrentResourceOwner = owner;