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: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Cached plans and statement generalization
Date: 2017-04-24 18:43:53
Message-ID: 20170424184353.u2krt2eiw2l6e2af@alap3.anarazel.de
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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.

Greetings,

Andres Freund

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