From: Brad Nicholson <bnichols@ca.afilias.info>
To: pgsql-performance@postgresql.org
Subject: Re: Memory usage - indexes
Date: Fri, 24 Sep 2010 15:24:54 -0400
Message-ID: <4C9CFB06.8090403@ca.afilias.info> (raw)
In-Reply-To: <173228.29370.qm@web39701.mail.mud.yahoo.com>
References: <173228.29370.qm@web39701.mail.mud.yahoo.com>
On 10-09-24 03:06 PM, Bob Lunney wrote:
> The pertinent difference between pg_stat_user_indexes and pg_statio_user_indexes is the latter shows the number of blocks read from disk or found in the cache.
I have a minor, but very important correction involving this point. The
pg_statio tables show you what blocks are found in the Postgres buffer
cache, and what ones are not.
For the ones that are not, those blocks may come from the OS filesystem
cache, a battery backed cache, or on the actual disk. There is a big
difference in performance based on where you are actually getting those
blocks from (and you can't this info from Postgres).
--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.
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To: pgsql-performance@postgresql.org
Cc: bnichols@ca.afilias.info
Subject: Re: Memory usage - indexes
In-Reply-To: <4C9CFB06.8090403@ca.afilias.info>
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