Re: Cached plans and statement generalization

From: Andres Freund <andres(at)anarazel(dot)de>
To: Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Douglas Doole <dougdoole(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Cached plans and statement generalization
Date: 2017-05-11 19:52:26
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On 2017-05-11 22:48:26 +0300, Konstantin Knizhnik wrote:
> On 05/11/2017 09:31 PM, Tom Lane wrote:
> > Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > > Good point. I think we need to do some measurements to see if the
> > > parser-only stage is actually significant. I have a hunch that
> > > commercial databases have much heavier parsers than we do.
> > FWIW, gram.y does show up as significant in many of the profiles I take.
> > I speculate that this is not so much that it eats many CPU cycles, as that
> > the constant tables are so large as to incur lots of cache misses. scan.l
> > is not quite as big a deal for some reason, even though it's also large.
> >
> > regards, tom lane
> Yes, my results shows that pg_parse_query adds not so much overhead:
> 206k TPS for my first variant with string literal substitution and modified query text used as hash key vs.
> 181k. TPS for version with patching raw parse tree constructed by pg_parse_query.

Those numbers and your statement seem to contradict each other?

- Andres

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