From: Alvaro Herrera <alvherre@commandprompt.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Greg Stark <gsstark@mit.edu>
Cc: Pierre C <lists@peufeu.com>
Cc: Greg Smith <greg@2ndquadrant.com>
Cc: Dave Crooke <dcrooke@gmail.com>
Cc: Paul McGarry <paul@paulmcgarry.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: shared_buffers advice
Date: Tue, 16 Mar 2010 19:20:58 -0300
Message-ID: <20100316222058.GI3037@alvh.no-ip.org> (raw)
In-Reply-To: <15417.1268776714@sss.pgh.pa.us>
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<4B9F3302.4020900@2ndquadrant.com>
<op.u9nrbeeteorkce@localhost>
<8285.1268749832@sss.pgh.pa.us>
<407d949e1003160753o6e5faa48rabaa42f7548029b7@mail.gmail.com>
<20100316213054.GG3037@alvh.no-ip.org>
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<15417.1268776714@sss.pgh.pa.us>
Tom Lane escribió:
> Alvaro Herrera <alvherre@commandprompt.com> writes:
> > Tom Lane escribió:
> >> Reorder to what, though? You still have the problem that we don't know
> >> much about the physical layout on-disk.
>
> > Well, to block numbers as a first step.
>
> fsync is a file-based operation, and we know exactly zip about the
> relative positions of different files on the disk.
Doh, right, I was thinking in the sync-file-range kind of API.
> > We had a customer that had a
> > performance problem because they were inserting lots of data to TOAST
> > tables, causing very frequent extensions. I kept wondering whether an
> > allocation policy that allocated several new blocks at a time could be
> > useful (but I didn't try it). This would also alleviate fragmentation,
> > thus helping the physical layout be more similar to logical block
> > numbers.
>
> That's not going to do anything towards reducing the actual I/O volume.
> Although I suppose it might be useful if it just cuts the number of
> seeks.
Oh, they had no problems with I/O volume. It was relation extension
lock that was heavily contended for them.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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Cc: alvherre@commandprompt.com, tgl@sss.pgh.pa.us, gsstark@mit.edu, lists@peufeu.com, greg@2ndquadrant.com, dcrooke@gmail.com, paul@paulmcgarry.com
Subject: Re: shared_buffers advice
In-Reply-To: <20100316222058.GI3037@alvh.no-ip.org>
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