| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Caching query plan costs |
| Date: | 2018-09-03 18:33:35 |
| Message-ID: | 20180903183335.GE25700@momjian.us |
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| Lists: | pgsql-hackers |
On Mon, Sep 3, 2018 at 01:30:33PM -0400, Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > What if we globally or locally cache the _cost_ of plans, so we can
> > consult that cache before planning and enable certain optimizations?
>
> But what would you use as cache key? And how's this help if we haven't
Uh, I assume we would do what pg_stat_statements does and remove the
constants an hash that.
> seen a similar query before in the session?
Well, if it was global we could use output from another session.
I guess my point is that this only used to turn on micro-optimizations
and maybe parallelism and JIT, so it doesn't have to be 100% accurate.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
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