Message-ID: <501C50FE.80905@agliodbs.com>
Date: Fri, 03 Aug 2012 15:30:22 -0700
From: Josh Berkus <josh@agliodbs.com>
Organization: PostgreSQL Experts Inc.
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To: pgsql-performance@postgresql.org
Subject: Re: Linux memory zone reclaim
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On 7/30/12 10:09 AM, Scott Marlowe wrote:
> I think the zone_reclaim gets turned on with a high ratio.  If the
> inter node costs were the same, and the intranode costs dropped in
> half, zone reclaim would likely get turned on at boot time.

We've been seeing a major problem with zone_reclaim and Linux, in that
Linux won't use the FS cache on the "distant" RAM *at all* if it thinks
that RAM is distant enough.  Thus, you get instances of seeing only half
of RAM used for FS cache, even though the database is 5X larger than RAM.

This is poor design on Linux's part, since even the distant RAM is
faster than disk.  For now, we've been disabling zone_reclaim entirely.

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