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Re: Postgres bug (working with iserverd)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Vadim Mikheev <vmikheev(at)sectorbase(dot)com>
Cc: Alexandr <AVShutko(at)mail(dot)khstu(dot)ru>, pgsql-bugs(at)postgreSQL(dot)org, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Postgres bug (working with iserverd)
Date: 2001-05-15 00:49:22
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugspgsql-hackers
I wrote:
> The direct cause of the problem is that EvalPlanQual isn't completely
> initializing the estate that it sets up for re-evaluating the plan.
> In particular it's not filling in es_result_relations and
> es_num_result_relations, which need to be set up if the top plan node
> is an Append.  (That's probably my fault.)  But there are a bunch of
> other fields that it's failing to copy, too.

I believe I have fixed this problem in CVS sources for current and
REL7_1, at least to the extent that EvalPlanQual processing produces
the right answers for updates/deletes in inheritance trees.

However, EvalPlanQual still leaks more memory than suits me ---
auxiliary memory allocated by the plan nodes is not recovered.
I think the correct way to implement it would be to create a new
memory context for each level of EvalPlanQual execution and use
that context as the "per-query context" for the sub-query.  The
whole context (including the copied plan) would be freed at the
end of the sub-query.  The notion of a stack of currently-unused
epqstate nodes would go away.

This would mean a few more cycles per tuple to copy the plan tree over
again each time, but I think that's pretty trivial compared to the plan
startup/shutdown costs that we incur anyway.  Besides, I have hopes of
making plan trees read-only whenever we do the fabled querytree
redesign, so the cost will someday go away.

Comments, objections?

			regards, tom lane

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