Re: Cached plans and statement generalization

On Tue, Apr 25, 2017 at 06:11:09PM +0300, Konstantin Knizhnik wrote:
> On 24.04.2017 21:43, Andres Freund wrote:
> > Hi,
> >
> > On 2017-04-24 11:46:02 +0300, Konstantin Knizhnik wrote:
> > > So what I am thinking now is implicit query caching. If the same query with
> > > different literal values is repeated many times, then we can try to
> > > generalize this query and replace it with prepared query with
> > > parameters.
> > That's not actuall all that easy:
> > - You pretty much do parse analysis to be able to do an accurate match.
> > How much overhead is parse analysis vs. planning in your cases?
> > - The invalidation infrastructure for this, if not tied to to fully
> > parse-analyzed statements, is going to be hell.
> > - Migrating to parameters can actually cause significant slowdowns, not
> > nice if that happens implicitly.
>
> Well, first of all I want to share results I already get: pgbench with
> default parameters, scale 10 and one connection:
>
> protocol
> TPS
> simple
> 3492
> extended
> 2927
> prepared
> 6865
> simple + autoprepare
> 6844

If this is string mashing on the unparsed query, as it appears to be,
it's going to be a perennial source of security issues.

Best,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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