From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org, Josh Berkus <josh@agliodbs.com>
Cc: Greg Smith <greg@2ndquadrant.com>
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
Date: Wed, 17 Nov 2010 02:12:29 +0100
Message-ID: <201011170212.30033.andres@anarazel.de> (raw)
In-Reply-To: <11113.1289955868@sss.pgh.pa.us>
References: <AANLkTi=n3zxiLNFhbpiN=JPQPwB=BhXf9iepw1KOEs8U@mail.gmail.com>
<201011170201.24782.andres@anarazel.de>
<11113.1289955868@sss.pgh.pa.us>
On Wednesday 17 November 2010 02:04:28 Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On Wednesday 17 November 2010 01:51:28 Tom Lane wrote:
> >> Well, there's a forced fsync after writing the last page of an xlog
> >> file, but I don't believe that proves that more than 16MB of xlog
> >> buffers is useless. Other processes could still be busy filling the
> >> buffers.
> >
> > Maybe I am missing something, but I think the relevant
> > AdvanceXLInsertBuffer() is currently called with WALInsertLock held?
>
> The fsync is associated with the write, which is not done with insert
> lock held. We're not quite that dumb.
Ah, I see. The XLogWrite in AdvanceXLInsertBuffer is only happening if the head
of the buffer gets to the tail - which is more likely if the wal buffers are
small...
Andres
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To: pgsql-performance@postgresql.org
Cc: andres@anarazel.de, tgl@sss.pgh.pa.us, josh@agliodbs.com, greg@2ndquadrant.com
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
In-Reply-To: <201011170212.30033.andres@anarazel.de>
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