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Re: pg_upgrade and statistics

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, 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>
Subject: Re: pg_upgrade and statistics
Date: 2012-03-15 00:26:06
Message-ID: 9684.1331771166@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Bruce Momjian <bruce(at)momjian(dot)us> writes:
> Does anyone know how bad the queries will be with only one target?

Bad.  That cycle seems like largely a waste of time.  About the only
thing it would do for you is ensure that relpages/reltuples are up to
date, which seems like something we could possibly arrange for during
the data import.

> I did see if vacuumdb --analyze-only was somehow being throttled by the
> vacuum settings, but saw the drive at 100% utilization analying a 36GB
> table on a 24GB RAM server, so it seems I/O bound.

I think it'd be good to explicitly set vacuum_cost_delay to 0 in the
first pass, in the same way as you are forcing
default_statistics_target, just in case somebody has a nondefault
setting for that.  The second pass could probably be allowed to use some
higher delay setting.

			regards, tom lane

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