From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
cc: Vitalii Tymchyshyn <tivv00@gmail.com>, pgsql-performance@postgresql.org,
	Gavin Flower <gavinflower@archidevsys.co.nz>,
	Simon Riggs <simon@2ndquadrant.com>
Subject: Re: In progress INSERT wrecks plans on table
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Comments: In-reply-to Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
	message dated "Sat, 11 May 2013 00:51:20 +1200"
Date: Fri, 10 May 2013 09:30:58 -0400
Message-ID: <3833.1368192658@sss.pgh.pa.us>
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Sender: pgsql-performance-owner@postgresql.org

Mark Kirkwood <mark.kirkwood@catalyst.net.nz> writes:
> Unfortunately a trigger will not really do the job - analyze ignores in 
> progress rows (unless they were added by the current transaction), and 
> then the changes made by analyze are not seen by any other sessions. So 
> no changes to plans until the entire INSERT is complete and COMMIT 
> happens (which could be a while - too long in our case).

I'm not sure I believe the thesis that plans won't change at all.
The planner will notice that the physical size of the table is growing.
That may not be enough, if the table-contents statistics are missing
or completely unreflective of reality, but it's something.

It is true that *already cached* plans won't change until after an
ANALYZE is done (the key point there being that ANALYZE sends out a
shared-inval message to force replanning of plans for the table).
Conceivably you could issue concurrent ANALYZEs occasionally while
the INSERT is running, not so much to update the stats --- because
they wouldn't --- as to force cached-plan invalidation.

			regards, tom lane


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