From: Mladen Gogala <mladen.gogala@vmsinfo.com>
To: pgsql-performance@postgresql.org
Subject: Re: Slow count(*) again...
Date: Wed, 13 Oct 2010 04:44:09 -0400
Message-ID: <4CB57159.2090501@vmsinfo.com> (raw)
In-Reply-To: <4CB55D7E.8080902@catalyst.net.nz>
References: <201010091626.18636.neil.whelchel@gmail.com>
<4CB2410C.6010603@postnewspapers.com.au>
<201010102115.58729.neil.whelchel@gmail.com>
<201010122347.20542.neil.whelchel@gmail.com>
<4CB55D7E.8080902@catalyst.net.nz>
On 10/13/2010 3:19 AM, Mark Kirkwood wrote:
> I think that major effect you are seeing here is that the UPDATE has
> made the table twice as big on disk (even after VACUUM etc), and it has
> gone from fitting in ram to not fitting in ram - so cannot be
> effectively cached anymore.
>
In the real world, tables are larger than the available memory. I have
tables of several hundred gigabytes in size. Tables shouldn't be
"effectively cached", the next step would be to measure "buffer cache
hit ratio", tables should be effectively used.
--
Mladen Gogala
Sr. Oracle DBA
1500 Broadway
New York, NY 10036
(212) 329-5251
www.vmsinfo.com
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Subject: Re: Slow count(*) again...
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