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Re: We probably need autovacuum_max_wraparound_workers

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: PgHacker <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: We probably need autovacuum_max_wraparound_workers
Date: 2012-06-29 02:15:19
Message-ID: 20120629021519.GR1267@tamriel.snowman.net (view raw or flat)
Thread:
Lists: pgsql-hackers
* Josh Berkus (josh(at)agliodbs(dot)com) wrote:
> I don't find Stephen's proposal of goal-based solutions to be practical.
>  A goal-based approach makes the assumption that database activity is
> predictable, and IME most databases are anything but.

We're talking about over the entire transaction space, and we can be
pretty liberal, in my view, with our estimates.  If we get it right, we
might risk doing more autovac's for wraparound than strictly necessary,
but they should happen over a sufficient time that it doesn't cause
performance issues.

One definite problem with this, of course, is that the wraparound
autovac can't be stopped and restarted, and anything that increases the
amount of wall-clock time required to complete the autovac will
necessairly increase the risk that we'll lose a bunch of work due to a
database restart.

	Thanks,

		Stephen

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