Re: Caching query plan costs

On Mon, Sep  3, 2018 at 01:30:33PM -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.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@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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