Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance

From: Kevin Grittner <kgrittn(at)ymail(dot)com>
To: Dave Chinner <david(at)fromorbit(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Jan Kara <jack(at)suse(dot)cz>, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Trond Myklebust <trondmy(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Joshua Drake <jd(at)commandprompt(dot)com>, James Bottomley <James(dot)Bottomley(at)hansenpartnership(dot)com>, Mel Gorman <mgorman(at)suse(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "lsf-pc(at)lists(dot)linux-foundation(dot)org" <lsf-pc(at)lists(dot)linux-foundation(dot)org>, Magnus Hagander <magnus(at)hagander(dot)net>
Subject: Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance
Date: 2014-01-14 23:03:39
Message-ID: 1389740619.41277.YahooMailNeo@web122305.mail.ne1.yahoo.com
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Dave Chinner <david(at)fromorbit(dot)com> write:

> Essentially, changing dirty_background_bytes, dirty_bytes and
> dirty_expire_centiseconds to be much smaller should make the
> kernel start writeback much sooner and so you shouldn't have to
> limit the amount of buffers the application has to prevent major
> fsync triggered stalls...

Is there any "rule of thumb" about where to start with these?  For
example, should a database server maybe have dirty_background_bytes
set to 75% of the non-volatile write cache present on the
controller, in an attempt to make sure that there is always some
"slack" space for writes?

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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