Message-ID: <518DD007.4000006@catalyst.net.nz>
Date: Sat, 11 May 2013 16:58:47 +1200
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
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Subject: Re: In progress INSERT wrecks plans on table
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On 11/05/13 01:30, Tom Lane wrote:
> 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.

Yeah - true, I was focusing on the particular type of query illustrated 
in the test case - pretty much entirely needing updated selectivity 
stats for a column, which wouldn't change unfortunately.

Cheers

Mark


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