Horton

Re: Adjust Memoize hit_ratio calculation

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>, "David G. Johnston" <david.g.johnston@gmail.com>
Date: 2023-03-21T19:48:16Z
Lists: pgsql-hackers 
On Tue, 21 Mar 2023 at 09:41, David Rowley <dgrowleyml@gmail.com> wrote:
> Because that's being changed in v16, I think it might also be a good
> idea to fix the hit_ratio calculation problem reported by David
> Johnston in [1].  In the attached, I've adjusted David's calculation
> slightly so that we divide by Max(ndistinct, est_cache_entries)
> instead of ndistinct.  This saves from overestimating when ndistinct
> is smaller than est_cache_entries.  I'd rather fix this now for v16
> than wait until v17 and further adjust the Memoize costing.

I've now pushed this change.

David

Commits

  1. Correct Memoize's estimated cache hit ratio calculation