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[SPAM] Re: shared_buffers advice

From: Ben Chobot <bench(at)silentmedia(dot)com>
To: Konrad Garus <konrad(dot)garus(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: [SPAM] Re: shared_buffers advice
Date: 2010-05-24 15:27:43
Message-ID: A2662635-A15D-4B71-B551-DC4020561DF9@silentmedia.com (view raw or flat)
Thread:
Lists: pgsql-performance
On May 24, 2010, at 4:25 AM, Konrad Garus wrote:

> Do shared_buffers duplicate contents of OS page cache? If so, how do I
> know if 25% RAM is the right value for me? Actually it would not seem
> to be true - the less redundancy the better.

You can look into the pg_buffercache contrib module. 

> Another question - is there a tool or built-in statistic that tells
> when/how often/how much a table is read from disk? I mean physical
> read, not poll from OS cache to shared_buffers.

Well, the pg_stat_* tables tell you how much logical IO is going on, but postgres has no way of knowing how effective the OS or disk controller caches are.

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