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Re: autovacuum

From: Chris Browne <cbbrowne(at)acm(dot)org>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: autovacuum
Date: 2006-02-01 17:54:42
Message-ID: 60lkwvklr1.fsf@dba2.int.libertyrms.com (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-hackers
alvherre(at)alvh(dot)no-ip(dot)org (Alvaro Herrera) writes:

> Chris Browne wrote:
>
>> It strikes me as a slick idea for autovacuum to take on that
>> behaviour.  If the daily backup runs for 2h, then it is quite futile
>> to bother vacuuming a table multiple times during that 2h period when
>> none of the tuples obsoleted during the 2h period will be able to be
>> cleaned out until the end.
>
> Hmm, yeah, sounds useful.  There's one implementation issue to notice
> however, and it's that the autovacuum process dies and restarts for each
> iteration, so there's no way for it to remember previous state unless
> it's saved somewhere permanent, as the stats info is.

Hmm.  It restarts repeatedly???  Hmmm...

> However this seems at least slightly redundant with the "maintenance
> window" feature -- you could set a high barrier to vacuum during the
> daily backup period instead.  (Anybody up for doing this job?)

In effect, this would be an alternative to the "window" feature.  You
open the window by starting pg_dump; pg_autovacuum would automatically
notice that as the eldest XID, and stop work until the pg_dump
actually finished.

In a way, it strikes me as more elegant; it would automatically notice
"backup windows," noticing *exact* start and end times...
-- 
select 'cbbrowne' || '@' || 'ntlug.org';
http://www.ntlug.org/~cbbrowne/linuxxian.html
"I'm sorry,  Mr.   Kipling, but you  just  don't know how to   use the
English Language."  -- Editor of the San Francisco Examiner, informing
Rudyard Kipling, who had one  article published in the newspaper, that
he needn't bother submitting a second, 1889

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