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Re: Database size Vs performance degradation

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Dave North" <DNorth(at)signiant(dot)com>
Cc: "Richard Huxton" <dev(at)archonet(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Database size Vs performance degradation
Date: 2008-07-30 15:05:16
Message-ID: 25537.1217430316@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
"Dave North" <DNorth(at)signiant(dot)com> writes:
> From: Richard Huxton [mailto:dev(at)archonet(dot)com] 
>> Well, that's pretty much the definition of bloat. Are you sure you're
>> vacuuming enough?

> DN: Well, the auto-vac is kicking off pretty darn frequently...around
> once every 2 minutes.  However, you just made me think of the obvious -
> is it actually doing anything?!  The app is pretty darn write intensive
> so I wonder if it's actually able to vacuum the tables?

IIRC, the default autovac parameters in 8.1 were pretty darn
unaggressive.  You should also check for long-running transactions
that might be preventing vacuum from removing recently-dead rows.

One of the reasons for updating off 8.1 is that finding out what autovac
is really doing is hard :-(.  I think it does log, but at level DEBUG2
or so, which means that the only way to find out is to accept a huge
amount of useless chatter in the postmaster log.  Newer releases have
a saner logging scheme.

			regards, tom lane

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