From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Subject: Re: Linux memory zone reclaim
Date: Fri, 03 Aug 2012 15:30:22 -0700
Message-ID: <501C50FE.80905@agliodbs.com> (raw)
In-Reply-To: <CAOR=d=2R5VKL2nEff3KpTWrLoZStyfOnAOwfeNC3b67ecSFJnw@mail.gmail.com>
References: <500616CB.3070408@2ndQuadrant.com>
<501673680200002500049227@gw.wicourts.gov>
<CAOR=d=2R5VKL2nEff3KpTWrLoZStyfOnAOwfeNC3b67ecSFJnw@mail.gmail.com>
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: josh@agliodbs.com
Subject: Re: Linux memory zone reclaim
In-Reply-To: <501C50FE.80905@agliodbs.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox