From: Neil Conway <neilc@samurai.com>
To: pryscila.lista@gmail.com
Cc: pgsql-performance@postgresql.org
Subject: Re: About method of PostgreSQL's Optimizer
Date: Tue, 13 Sep 2005 19:16:26 -0400
Message-ID: <43275DCA.7040006@samurai.com> (raw)
In-Reply-To: <cf0868bd05091315503024742@mail.gmail.com>
References: <cf0868bd05091315503024742@mail.gmail.com>
Pryscila B Guttoski wrote:
> On my master course, I'm studying the PostgreSQL's optimizer.
> I don't know if anyone in this list have been participated from the
> PostgreSQL's Optimizer development, but maybe someone can help me on this
> question.
pgsql-hackers might be more appropriate.
> PostgreSQL generates all possible plans of executing the query (using an
> almost exhaustive search), then gives a cost to each plan and finally the
> cheapest one is selected for execution.
> There are other methods for query optimization, one of them is based on plan
> transformations (for example, using A-Star algorithm) instead of plan
> constructions used by PostgreSQL.
Right, the main query planner uses a nearly-exhaustive search. For
queries with many joins (when the cost of an exhaustive search would be
prohibitive), "GEQO" is used, which uses a genetic algorithm to avoid an
exhaustive search of the solution space.
> Does anyone know why this method was choosen?
As far as I know, the main planner algorithm is fairly standard and is
mainly different from System R's canonical algorithm in the details,
like whether non-left-deep plans are pruned.
> Are there any papers or researches about it?
There are many papers on the System R algorithm and similar techniques,
which should explain the basic motivations for the design. I'm not aware
of any papers specifically on the PostgreSQL query optimizer, although
there have been a few presentations on it:
http://neilc.treehou.se/optimizer.pdfhttp://conferences.oreillynet.com/presentations/os2003/lane_tom.pdf
-Neil
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To: pgsql-performance@postgresql.org
Cc: neilc@samurai.com, pryscila.lista@gmail.com
Subject: Re: About method of PostgreSQL's Optimizer
In-Reply-To: <43275DCA.7040006@samurai.com>
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