Re: Patches for TODO item: Avoid truncating empty OCDR temp tables on COMMIT

On 15.01.2013 21:03, Tom Lane wrote:
> Robert Haas<robertmhaas(at)gmail(dot)com> writes:
>> On the third hand, the fact that a table is OCDR is recorded in
>> backend-local storage somewhere, and that storage (unlike the
>> relcache) had better be reliable. So maybe there's some way to
>> finesse it that way.
>
> Hm, keep a flag in that storage you mean? Yeah, that could possibly
> work.

Sounds reasonable.

Until someone gets around to write a patch along those lines, I'm
inclined to apply this one liner:

*** a/src/backend/commands/tablecmds.c
--- b/src/backend/commands/tablecmds.c
***************
*** 10124,10130 **** PreCommit_on_commit_actions(void)
/* Do nothing (there shouldn't be such entries, actually) */
break;
case ONCOMMIT_DELETE_ROWS:
! oids_to_truncate = lappend_oid(oids_to_truncate, oc->relid);
break;
case ONCOMMIT_DROP:
{
--- 10124,10136 ----
/* Do nothing (there shouldn't be such entries, actually) */
break;
case ONCOMMIT_DELETE_ROWS:
! /*
! * If this transaction hasn't accessed any temporary relations,
! * we can skip truncating ON COMMIT DELETE ROWS tables, as
! * they must still be empty.
! */
! if (MyXactAccessedTempRel)
! oids_to_truncate = lappend_oid(oids_to_truncate, oc->relid);
break;
case ONCOMMIT_DROP:
{

We already have that MyXactAccessedTempRel global flag. Just checking
that should cover many common cases.

- Heikki