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Re: [PERFORM] autovacuum on a -mostly- r/o table

From: Tobias Brox <tobias(at)nordicbet(dot)com>
To: "Matthew T(dot) O'Connor" <matthew(at)zeut(dot)net>
Cc: Tobias Brox <tobias(at)nordicbet(dot)com>,Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Edoardo Ceccarelli <eddy(at)axa(dot)it>,postgres performance list <pgsql-performance(at)postgresql(dot)org>,pgsql-admin(at)postgresql(dot)org
Subject: Re: [PERFORM] autovacuum on a -mostly- r/o table
Date: 2006-10-15 14:52:12
Message-ID: 20061015145212.GA13175@oppetid.no (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-performance
[Matthew T. O'Connor - Sun at 10:42:34AM -0400]
> Yeah, I think if the delay settings are too high it can cause problems, 
> that's part of the reason we have yet to turn these on be default since 
> we won't have enough data to suggest good values.  Can you tell us what 
> settings you finally settled on?

I'm still not yet settled, and the project manager is critical to
autovacuum (adds complexity, no obvious benefits from it, we see from
the CPU graphs that it's causing iowait, iowait is bad).  We're going to
run autovacuum biweekly now to see what effect it has on the server
load.

I've been using the cost/delay-setting of 200/200 for a week now, and
I'm going to continue with 100/150 for a while.  

Are there any known disadvantages of lowering both values to the extreme
- say, 20/20 instead of 200/200?  That would efficiently mean "sleep as
often as possible, and sleep for 1 ms for each cost unit spent" if
I've understood the system right.

Are there any logs that can help me, and eventually, are there any
ready-made scripts for checking when autovacuum is running, and
eventually for how long it keeps its transactions?  I'll probably write
up something myself if not.


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