From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Huxton <dev@archonet.com>
Cc: jlparkinson@bigpond.com
Cc: pgsql-sql@postgresql.org
Subject: Re: Slow Multi-joins performance [DEVELOPERS attn please]
Date: Mon, 09 Sep 2002 16:26:42 -0400
Message-ID: <13474.1031603202@sss.pgh.pa.us> (raw)
In-Reply-To: <200209091624.08766.dev@archonet.com>
References: <02090620595601.02695@localhost>
<200209091624.08766.dev@archonet.com>
Richard Huxton <dev@archonet.com> writes:
> Which says to me that your form is fine. Testing says otherwise, so there must
> be some element of the query that is not being accounted for in EXPLAIN
> ANALYSE.
To wit, planning time. EXPLAIN ANALYZE only counts execution time.
And planning time on a 13-way join is going to be nontrivial ---
especially compared to execution against trivial-size tables.
You can turn on some query stats logging (I forget the SET-variable
names) to get a feeling for the relative costs of planning and
execution; but usually planning drops into the noise once you start
looking at production-sized cases.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, dev@archonet.com, jlparkinson@bigpond.com
Subject: Re: Slow Multi-joins performance [DEVELOPERS attn please]
In-Reply-To: <13474.1031603202@sss.pgh.pa.us>
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