On 02/04/2014 11:58 PM, Andres Freund wrote:
On February 4, 2014 10:50:10 PM CET, Peter Geoghegan <p...@heroku.com> wrote:
On Tue, Feb 4, 2014 at 11:11 AM, Andres Freund <and...@2ndquadrant.com>
wrote:
Does this feature relate to compression of WAL page images at all?
No.
So the obvious question is: where, if anywhere, do the two efforts
(this patch, and Fujii's patch) overlap? Does Fujii have any concerns
about this patch as it relates to his effort to compress FPIs?
I think there's zero overlap. They're completely complimentary features. It's
not like normal WAL records have an irrelevant volume.
Correct. Compressing a full-page image happens on the first update after
a checkpoint, and the diff between old and new tuple is not used in that
case.
Compressing full page images makes a difference if you're doing random
updates across a large table, so that you only update each buffer 1-2
times. This patch will have no effect in that case. And when you update
the same page many times between checkpoints, the full-page image is
insignificant, and this patch has a big effect.
- Heikki
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