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Re: High memory usage

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Ross J(dot) Reedstrom" <reedstrm(at)rice(dot)edu>
Cc: Rainer Mager <rmager(at)vgkk(dot)com>, PostgreSQL Admin <pgsql-admin(at)postgresql(dot)org>
Subject: Re: High memory usage
Date: 2001-06-21 02:52:28
Message-ID: 11773.993091948@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-jdbcpgsql-patches
"Ross J. Reedstrom" <reedstrm(at)rice(dot)edu> writes:
> My guess is it's an interaction of the optimizer with the plan for this
> query, which might have many, nearly identical cost plans, since 8 of
> the 9 tables are actually the same table.

Yes, I suspect the same.  A large fraction of the possible subplans
would have exactly identical costs, which would keep the planner from
discarding any of them (normally, it drops clearly-inferior subplans
instantly, which does a great deal to limit exponential search
behavior).  It doesn't help any that the WHERE conditions are all
so similar, either.

I have a strong suspicion that the database schema is poorly thought
out, but lacking any concrete info, it's hard to offer suggestions
for improvement.

			regards, tom lane

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