From 895a94de6dffa71741586a2228275f66db03f8ca Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 30 Nov 2007 21:22:54 +0000 Subject: Avoid incrementing the CommandCounter when CommandCounterIncrement is called but no database changes have been made since the last CommandCounterIncrement. This should result in a significant improvement in the number of "commands" that can typically be performed within a transaction before hitting the 2^32 CommandId size limit. In particular this buys back (and more) the possible adverse consequences of my previous patch to fix plan caching behavior. The implementation requires tracking whether the current CommandCounter value has been "used" to mark any tuples. CommandCounter values stored into snapshots are presumed not to be used for this purpose. This requires some small executor changes, since the executor used to conflate the curcid of the snapshot it was using with the command ID to mark output tuples with. Separating these concepts allows some small simplifications in executor APIs. Something for the TODO list: look into having CommandCounterIncrement not do AcceptInvalidationMessages. It seems fairly bogus to be doing it there, but exactly where to do it instead isn't clear, and I'm disinclined to mess with asynchronous behavior during late beta. --- src/backend/commands/async.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'src/backend/commands/async.c') diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c index 55b99f8c922..c32dd2b19fc 100644 --- a/src/backend/commands/async.c +++ b/src/backend/commands/async.c @@ -7,7 +7,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.136 2007/04/12 06:53:46 neilc Exp $ + * $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.137 2007/11/30 21:22:53 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -562,7 +562,8 @@ AtCommit_Notify(void) */ result = heap_update(lRel, &lTuple->t_self, rTuple, &update_ctid, &update_xmax, - GetCurrentCommandId(), InvalidSnapshot, + GetCurrentCommandId(true), + InvalidSnapshot, false /* no wait for commit */ ); switch (result) { -- cgit v1.2.3