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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: AJ Weber <aweber@comcast.net>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: autovacuum fringe case?
Date: Wed, 23 Jan 2013 23:03:04 -0300
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AJ Weber escribió:

> On 1/23/2013 2:13 PM, Jeff Janes wrote:

> >Scheduling a manual vacuum should be fine (but keep in mind that
> >vacuum has very different default cost_delay settings than autovacuum
> >does.  If the server is completely idle that shouldn't matter, but if
> >it is only mostly idle, you might want to throttle the IO a bit).  But
> >I certainly would not disable autovacuum without further evidence.  If
> >a table only needs to be vacuumed once a day and you preemptively do
> >it at 3a.m., then autovac won't bother to do it itself during the day.
> >  So there is no point, but much risk, in also turning autovac off.
> If I set autovacuum_max_workers = 1, will that effectively
> single-thread it so I don't have two running at once?  Maybe that'll
> mitigate disk contention a little at least?

If you have a single one, it will go three times as fast.  If you want
to make the whole thing go slower (i.e. cause less impact on your I/O
system when running), crank up autovacuum_vacuum_cost_delay.

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services


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