Re: Optimizing Multiply Joins ???

From: Meszaros Attila <tilla(at)draconis(dot)elte(dot)hu>
To: pgsql-sql(at)hub(dot)org
Subject: Re: Optimizing Multiply Joins ???
Date: 2000-09-13 19:22:45
Message-ID: Pine.LNX.3.96.1000913211618.18199T-100000@draconis.csoma.elte.hu
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Hi,

> That's interesting; apparently the regular optimizer is faster than the
> GEQO optimizer for your style of query. Try increasing the GEQO
> threshold (pg_option "geqo_rels") to more than 11.
Changing this option in a psql session with 'set' has really helped
Thanks.
the results have changed this way:
nr tables plain(s): more indices(2): geqo off(s):
10: 0.2 0.3 0.3
11: 4.8 5.9 0.8
12: 5.2 7.0 1.8

But it seems, geqo_rels option is not parsed from the pg_option
file.

> Actually, as the 7.1 code currently stands, a query that uses explicit
> JOIN operators like yours does will always be implemented in exactly
> the given join order, with no searching. I haven't quite decided if
> that's a bug or a feature ...
Great !!
If possible, it should be left in the codebase at least as an
option later...
Because we could have dozens(hundreds) of preoptimized queries.

Attila

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