Message-ID: <1367911165.32561.7.camel@matt-ultrabook>
Subject: Re: In progress INSERT wrecks plans on table
From: Matt Clarkson <mattc@catalyst.net.nz>
To: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
Cc: Simon Riggs <simon@2ndQuadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>, Gavin
	Flower <gavinflower@archidevsys.co.nz>, "pgsql-performance@postgresql.org"
	<pgsql-performance@postgresql.org>
Date: Tue, 07 May 2013 19:19:25 +1200
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On Tue, 2013-05-07 at 18:32 +1200, Mark Kirkwood wrote:
> On 07/05/13 18:10, Simon Riggs wrote:
> > On 7 May 2013 01:23,  <mark.kirkwood@catalyst.net.nz> wrote:
> >
> >> I'm thinking that a variant of (2) might be simpler to inplement:
> >>
> >> (I think Matt C essentially beat me to this suggestion - he originally
> >> discovered this issue). It is probably good enough for only *new* plans to
> >> react to the increased/increasing number of in progress rows. So this
> >> would require backends doing significant numbers of row changes to either
> >> directly update pg_statistic or report their in progress numbers to the
> >> stats collector. The key change here is the partial execution numbers
> >> would need to be sent. Clearly one would need to avoid doing this too
> >> often (!) - possibly only when number of changed rows >
> >> autovacuum_analyze_scale_factor proportion of the relation concerned or
> >> similar.
> >
> > Are you loading using COPY? Why not break down the load into chunks?
> >
> 
> INSERT - but we could maybe workaround by chunking the INSERT. However 
> that *really* breaks the idea that in SQL you just say what you want, 
> not how the database engine should do it! And more practically means 
> that the most obvious and clear way to add your new data has nasty side 
> effects, and you have to tip toe around muttering secret incantations to 
> make things work well :-)

We also had the same problem with an UPDATE altering the data
distribution in such a way that trivial but frequently executed queries
cause massive server load until auto analyze sorted out the stats.

-- 
Matt Clarkson
Catalyst.Net Limited


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