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Re: Clarification Needed: When does autovacuum daemon run?

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Narasimha Murthy-VRFX87 <vrfx87(at)motorola(dot)com>
Cc: Ian Lea <ian(dot)lea(at)gmail(dot)com>, Devrim GÜNDÜZ <devrim(at)gunduz(dot)org>, pgsql-admin <pgsql-admin(at)postgresql(dot)org>
Subject: Re: Clarification Needed: When does autovacuum daemon run?
Date: 2010-05-20 17:20:04
Message-ID: 1274375829-sup-7935@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-admin
Excerpts from Narasimha Murthy-VRFX87's message of jue may 20 02:47:21 -0400 2010:
> Hi Alvaro Herrera,
> 
> Since, my original plan was to run the auto-vacuum daily EXACTLY at 5 am, I wanted to know which seconds of a minute. My query in other word was, if I set autovacuum_naptime to 1 hr, which minute of an hour the auto-vacuum runs (oth min, 15th min or something else).

Yeah, you have no way to be know.  I guess you could turn autovacuum off
in postgresql.conf all day, and exactly at 5am you have a cron job that
edits postgresql.conf and reloads Postgres.  This would start up
autovacuum, which would then continue with the regular schedule.
This is hardly ideal; there were plans to improve on this by having an
autovacuum schedule, but I think the demand for this feature has
decreased considerable, so I haven't given it any minute's thought.

> From the clarification given by the you and other community members, I now understood that autovacuum is designed to run frequently in the background, not designed to run once a day at a specific time. Due to this design intent, autovacuum_naptime is set to 1 min by default and autovacuum runs lazy/plain/standard vacuum commands (so that Vacuum can run concurrently with other normal DB operations).

Correct.
-- 

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