From: Andres Freund <andres@anarazel.de>
To: pgsql-performance@postgresql.org
Cc: Greg Smith <greg@2ndquadrant.com>
Cc: Marti Raudsepp <marti@juffo.org>
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
Date: Mon, 1 Nov 2010 00:10:28 +0100
Message-ID: <201011010010.28724.andres@anarazel.de> (raw)
In-Reply-To: <4CCDCAA3.4050805@2ndquadrant.com>
References: <AANLkTi=n3zxiLNFhbpiN=JPQPwB=BhXf9iepw1KOEs8U@mail.gmail.com>
<4CCDCAA3.4050805@2ndquadrant.com>
On Sunday 31 October 2010 20:59:31 Greg Smith wrote:
> Writes only are sync'd out when you do a commit, or the database does a
> checkpoint.
Hm? WAL is written out to disk after an the space provided by wal_buffers(def
8) * XLOG_BLCKSZ (def 8192) is used. The default is 64kb which you reach
pretty quickly - especially after a checkpoint. With O_D?SYNC that will
synchronously get written out during a normal XLogInsert if hits a page
boundary.
*Additionally* its gets written out at a commit if sync commit is not on.
Not having a real O_DSYNC on linux until recently makes it even more dubious
to have it as a default...
Andres
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To: pgsql-performance@postgresql.org
Cc: andres@anarazel.de, greg@2ndquadrant.com, marti@juffo.org
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
In-Reply-To: <201011010010.28724.andres@anarazel.de>
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