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Re: Problems with autovacuum

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Łukasz Jagiełło <lukasz(dot)jagiello(at)gforces(dot)pl>, Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Problems with autovacuum
Date: 2009-05-26 23:59:19
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> However I think there's a bigger problem here, which is that if the user
> has set naptime too low, i.e. to a value lower than
> number-of-databases * 100ms, we'll be running the (expensive)
> rebuild_database_list function on each iteration ... maybe we oughta put
> a lower bound on naptime based on the number of databases to avoid this
> problem.

Bingo, that's surely exactly what was happening to the OP.  He had 2000
databases and naptime at (I assume) the default; so he was rerunning
rebuild_database_list every 100ms.

So that recovery code path needs some more thought.  Maybe a lower bound
on how often to do rebuild_database_list?  And/or don't set adl_next_worker
to less than 100ms in the future to begin with?

			regards, tom lane

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