Re: performance regression in 9.2/9.3 - Mailing list pgsql-hackers

From Merlin Moncure
Subject Re: performance regression in 9.2/9.3
Date
Msg-id CAHyXU0xH8SC+KfaNd69vFh=S3=puSvD75KNKJXisknA6JiB17Q@mail.gmail.com
Whole thread Raw
In response to Re: performance regression in 9.2/9.3  (Linos <info@linos.es>)
Responses Re: performance regression in 9.2/9.3  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
On Thu, Jun 5, 2014 at 9:54 AM, Linos <info@linos.es> wrote:
> What I don't understand is why the statistics have this bad information, all my tests are done on a database just
restoredand analyzed. Can I do something to improve the quality of my database statistics and let the planner do better
choices?Maybe increase the statistics target of the columns involved? 

By that I meant row count estimates coming out of the joins are way
off.  This is pushing the planner into making bad choices.  The most
pervasive problem I see is that the row count estimate boils down to
'1' at some juncture causing the server to favor nestloop/index scan
when something like a hash join would likely be more appropriate.

merlin



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