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Re: Problems with autovacuum

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
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 18:41:15
Message-ID: 20090526184115.GI32650@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-performance
Tom Lane escribió:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > Tom Lane escribi:
> >> I believe the interpretation of autovacuum_naptime is that it should
> >> examine each database that often, ie once a minute by default.  So
> >> it's got more than 30 databases per second to look through.
> 
> > Note that this is correct in 8.1 and 8.2 but not 8.3 onwards.
> 
> Oh?  The current documentation still defines the variable thusly:
> 
> 	Specifies the minimum delay between autovacuum runs on any given
> 	database. In each round the daemon examines the database and
> 	issues VACUUM and ANALYZE commands as needed for tables in that
> 	database.

Sorry, it's the other way around actually -- correct for 8.3 onwards,
wrong for 8.1 and 8.2.  In the earlier versions, it would do one run in
a chosen database, sleep during "naptime", then do another run.

> I suppose the use of "minimum" means that this is not technically
> incorrect, but it's sure not very helpful if there is some other
> rule involved that causes it to not behave as I said.  (And if there
> is some other rule, what is that?)

The word "minimum" is there because it's possible that all workers are
busy with some other database(s).

> Please improve the docs.

I'll see about that.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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