From: uwcssa <uwcssa@gmail.com>
To: pgsql-performance@postgresql.org
Subject: postgresql geqo optimization
Date: Fri, 10 Feb 2006 20:46:14 -0500
Message-ID: <f2f562510602101746g2542a08aod0bbb16787f4eb31@mail.gmail.com> (raw)
I have a question with regard to GEQO optimizer of Postgresql.
For complex queries with over 12 tables in a join, (12 is the
default value), the Postgresql optimizer by default will not use the dynamic
programming style optimizer. Instead, it uses genetic algorithm to compute a
sub-optimal query plan. The reason is that GEQO takes sub-seconds to find a
query plan while the DP style optimizer will take minutes or even hours to
optimize a complex query with large join degree.
I am wondering if anyone here ever had complex queries that the GEQO fails
to work properly, i.e., finds a terrible query plan as compared to one
found by DP optimizer (by forcing Postgresql always uses DP). This is
important to me since I am trying to see what type of queries will be worth
spending a lot of time doing a thorough DP optimization (if it is going to
be executed again and again).
thanks a lot!
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To: pgsql-performance@postgresql.org
Cc: uwcssa@gmail.com
Subject: Re: postgresql geqo optimization
In-Reply-To: <f2f562510602101746g2542a08aod0bbb16787f4eb31@mail.gmail.com>
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