From: | Andres Freund <andres(at)anarazel(dot)de> |
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To: | pgsql-hackers(at)postgresql(dot)org |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Marti Raudsepp <marti(at)juffo(dot)org> |
Subject: | Re: [PATCH] Revert default wal_sync_method to fdatasync on Linux 2.6.33+ |
Date: | 2010-11-05 20:54:57 |
Message-ID: | 201011052154.57775.andres@anarazel.de |
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Lists: | pgsql-hackers |
On Friday 05 November 2010 19:13:47 Tom Lane wrote:
> Marti Raudsepp <marti(at)juffo(dot)org> writes:
> > PostgreSQL's default settings change when built with Linux kernel
> > headers 2.6.33 or newer. As discussed on the pgsql-performance list,
> > this causes a significant performance regression:
> > http://archives.postgresql.org/pgsql-performance/2010-10/msg00602.php
> >
> > NB! I am not proposing to change the default -- to the contrary --
> > this patch restores old behavior.
>
> I'm less than convinced this is the right approach ...
>
> If open_dsync is so bad for performance on Linux, maybe it's bad
> everywhere? Should we be rethinking the default preference order?
I fail to see how it could be beneficial on *any* non-buggy platform.
Especially with small wal_buffers and larger commits (but also otherwise) it
increases the amount of synchronous writes the os has to do tremendously.
* It removes about all benefits of XLogBackgroundFlush()
* It removes any chances of reordering after writing.
* It makes AdvanceXLInsertBuffer synchronous if it has to write outy
Whats the theory about placing it so high in the preferences list?
Andres
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