From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Michael McCarthy <michael(at)tcsi(dot)com> |
Cc: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: [SQL] problem with OR'ed AND queriess |
Date: | 1999-12-22 00:02:00 |
Message-ID: | 13399.945820920@sss.pgh.pa.us |
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Lists: | pgsql-sql |
Michael McCarthy <michael(at)tcsi(dot)com> writes:
> I have traced the backend server in a debugger; a stack trace is attached
> below. What I see in examining the code is a recursive normalization of
> the query; postgres is running out of memory trying to convert the OR'ed
> ANDs query to conjunctive normal form (CNF).
Yes, the CNF-conversion code is pretty awful. I have reduced its
badness somewhat in current sources, but really we need to rethink the
whole problem --- for queries that are naturally expressed as
OR-of-ANDs, forcing the condition into AND-of-ORs is a loser.
You could try folding prepqual.c from current sources (get the nightly
snapshot or use CVS) into 6.5. I'm not sure it would merge cleanly,
but it'd beat reinventing the fixes I made.
regards, tom lane
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