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Re: auto-sizing wal_buffers

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: auto-sizing wal_buffers
Date: 2011-01-17 01:15:46
Message-ID: AANLkTi=Dgn-3jRj+QUMCunMgicwifZENHXKnKMuTQWA5@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sun, Jan 16, 2011 at 7:34 AM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
> I think we can be more specific on that last sentence; is there even any
> *theoretical* benefit to settings above 16MB, the size of a WAL segment?
>  Certainly there have been no test results to show any.

If the workload generates 16MB or more WAL for wal_writer_delay,
16MB or more of wal_buffers would be effective. In that case,
wal_buffers is likely to be filled up with unwritten WAL, then you have
to write buffers while holding WALInsert lock. This is obviously not
good.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

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