Re: Slow Multi-joins performance [DEVELOPERS attn please] - Mailing list pgsql-sql

From Tom Lane
Subject Re: Slow Multi-joins performance [DEVELOPERS attn please]
Date
Msg-id 13474.1031603202@sss.pgh.pa.us
Whole thread Raw
In response to Re: Slow Multi-joins performance [DEVELOPERS attn please]  (Richard Huxton <dev@archonet.com>)
Responses Re: Slow Multi-joins performance [DEVELOPERS attn please]  (jlparkinson@bigpond.com <jlparkinson@bigpond.com>)
List pgsql-sql
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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