Re: pg_upgrade and statistics

Kevin Grittner <kevin.grittner@wicourts.gov>

From: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>

To: "Bruce Momjian" <bruce@momjian.us>

Cc: "Peter Eisentraut" <peter_e@gmx.net>, "Daniel Farina" <daniel@heroku.com>,"Greg Stark" <stark@mit.edu>, "pgsql-hackers" <pgsql-hackers@postgresql.org>, "Tom Lane" <tgl@sss.pgh.pa.us>

Date: 2012-03-13T22:33:29Z

Lists: pgsql-hackers

Bruce Momjian <bruce@momjian.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