| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
| Subject: | Re: Adjust Memoize hit_ratio calculation |
| Date: | 2023-03-21 19:48:16 |
| Message-ID: | CAApHDvqOm_ANNwXdJQFSA2g_tszgDeWGJ+_M3FiyUzN9XnEutw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, 21 Mar 2023 at 09:41, David Rowley <dgrowleyml(at)gmail(dot)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
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