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Re: pg_upgrade and statistics

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Bruce Momjian" <bruce(at)momjian(dot)us>
Cc: "Peter Eisentraut" <peter_e(at)gmx(dot)net>, "Daniel Farina" <daniel(at)heroku(dot)com>,"Greg Stark" <stark(at)mit(dot)edu>, "pgsql-hackers" <pgsql-hackers(at)postgresql(dot)org>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: pg_upgrade and statistics
Date: 2012-03-13 22:33:29
Message-ID: 4F5F84E90200002500046273@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-hackers
Bruce Momjian <bruce(at)momjian(dot)us> wrote:
 
> What is the target=10 duration?  I think 10 is as low as we can
> acceptably recommend.  Should we recommend they run vacuumdb
> twice, once with default_statistics_target = 4, and another with
> the default?
 
Here are the results at various settings.
 
1   :  172198.892 ms
2   :  295536.814 ms
4   :  474319.826 ms
10  :  750458.312 ms
100 :  3433794.609 ms
 
I'm not sure what's best for a general approach to the problem.  For
my own part, I'd be inclined to cherry-pick tables if I were in a
hurry.
 
I hope we at least bring over relpages and reltuples, to give the
optimizer *some* clue what it's looking at.  I wouldn't thing those
would be changing semantics or format very often.
 
-Kevin

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