Message-ID: <4BB197B3.3050306@agliodbs.com>
Date: Mon, 29 Mar 2010 23:18:27 -0700
From: Josh Berkus <josh@agliodbs.com>
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To: Richard Yen <dba@richyen.com>
CC: pgsql-performance@postgresql.org
Subject: Re: why does swap not recover?
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On 3/26/10 4:57 PM, Richard Yen wrote:
> I'm planning on lowering the shared_buffers to a more sane value, like 25GB (pgtune recommends this for a Mixed-purpose machine) or less (pgtune recommends 14GB for an OLTP machine).  However, before I do this (and possibly resolve the issue), I was hoping to see if anyone would have an explanation for the constant reading from swap, but never writing back.

Postgres does not control how swap is used.  This would be an operating
system issue.  Leaving aside the distict possibility of a bug in
handling swap (nobody seems to do it well), there's the distinct
possibility that you're actually pinning more memory on the system than
it has (through various processes) and it's wisely shifted some
read-only files to the swap (as opposed to read-write ones).  But that's
a fairly handwavy guess.

-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com