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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@2ndquadrant.com>
cc: KONDO Mitsumasa <kondo.mitsumasa@lab.ntt.co.jp>,
 Robert Haas <robertmhaas@gmail.com>,
 Heikki Linnakangas <hlinnakangas@vmware.com>,
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Subject: Re: Improvement of checkpoint IO scheduler for stable transaction
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Comments: In-reply-to Andres Freund <andres@2ndquadrant.com>
 message dated "Thu, 04 Jul 2013 15:05:55 +0200"
Date: Thu, 04 Jul 2013 11:21:05 -0400
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Andres Freund <andres@2ndquadrant.com> writes:
> I don't like going in this direction at all:
> 1) it breaks pg_upgrade. Which means many of the bigger users won't be
>    able to migrate to this and most packagers would carry the old
>    segsize around forever.
>    Even if we could get pg_upgrade to split files accordingly link mode
>    would still be broken.

TBH, I think *any* rearrangement of the on-disk storage files is going
to be rejected.  It seems very unlikely to me that you could demonstrate
a checkpoint performance improvement from that that occurs consistently
across different platforms and filesystems.  And as Andres points out,
the pain associated with it is going to be bad enough that a very high
bar will be set on whether you've proven the change is worthwhile.

			regards, tom lane


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