MIME-Version: 1.0
References: <CAP53Pky29GWAVVk3oBgKBDqhND0BRBN6yTPeguV_qSivFL5N_g@mail.gmail.com>
 <1161645.1742854534@sss.pgh.pa.us> <CAP53Pky44MuEYPDFcqR+ogffnifbuXkAWi5TvjhHmpSdj88o8w@mail.gmail.com>
 <1164845.1742856354@sss.pgh.pa.us> <CA+TgmoZ8qXiZmmn4P9Mk1cf2mjMMLFPOjSasCjuKSiHFcm-ncw@mail.gmail.com>
 <3ba16aa7-3cb2-4289-b773-522ae2f03a77@tantorlabs.com> <81ef0f5a-b6a1-4417-ae3a-2bae9b8d419e@gmail.com>
 <67b5c84a-dedd-4103-af7e-0117046102fe@tantorlabs.com> <580fe72c-85be-45a8-9e00-6b5417690557@tantorlabs.com>
 <CAApHDvpT0Y1BfYgeWz+PkKaLBEff1izYOAjNSibhBTNFEdqLtg@mail.gmail.com>
 <CA+TgmobDHmaNTqi5yLPJoW6fTCuiWOgF9CSCSHX_OTLmGxYRUQ@mail.gmail.com>
 <CAApHDvqYL3OVvOsyvEPsDJ7h4zQh=LEygQgcQSN-TemRJLMb6Q@mail.gmail.com>
 <3ea66a50-e4b0-4f20-ae0c-4d9cbaf81cfb@tantorlabs.com> <CAApHDvpuM8jW-BGu7B=i6uv+jmndEo-2z_BYvj5JNmx=qV-uSQ@mail.gmail.com>
 <0e8dc4fa-3655-4e9f-9424-9b32a15e6acd@tantorlabs.com> <CAApHDvqmyHuEt7rdFLJr4cZecbhno5OZ6iL5EQNNu9Oi1f93sQ@mail.gmail.com>
 <7e995158-157e-4ec6-a7c8-266c1a6f7b43@tantorlabs.com>
In-Reply-To: <7e995158-157e-4ec6-a7c8-266c1a6f7b43@tantorlabs.com>
From: David Rowley <dgrowleyml@gmail.com>
Date: Fri, 18 Apr 2025 09:29:37 +1200
Message-ID: <CAApHDvq0Zz3+nh9hPRBP-oAocFZETfhdE_jcN8aG+Thc24Zk5g@mail.gmail.com>
Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost adjustment
To: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, 
	Lukas Fittl <lukas@fittl.com>, Daniel Gustafsson <daniel@yesql.se>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, 
	Nikolay Samokhvalov <samokhvalov@gmail.com>, Andrei Lepikhov <lepihov@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Archived-At: <https://www.postgresql.org/message-id/CAApHDvq0Zz3%2Bnh9hPRBP-oAocFZETfhdE_jcN8aG%2BThc24Zk5g%40mail.gmail.com>
Precedence: bulk

On Wed, 16 Apr 2025 at 10:09, Ilia Evdokimov
<ilya.evdokimov@tantorlabs.com> wrote:
> I've prepared the updated patches as discussed, including the addition
> of estimated lookups in the EXPLAIN output for Memoize. Please let me
> know if you have any feedback or further suggestions.

While this is fresh, as I might forget before the July CF...

I know I did suggest that the hit_ratio should be a percent and it
should be multiplied by 100.0.  This seems fine for the text format as
you can have the % unit there. However, looking at
ExplainPropertyFloat(), we don't print the unit for non-text formats.
I wonder if printing a number between 0 and 100 there will be
confusing. I don't believe we have anything else in EXPLAIN that shows
a percentage. I don't quite know what to do about this. One thought I
had was to only * 100 for text format, but that might be more
confusing.

Aside from that, I'd prefer the new fields in struct Memoize to be
prefixed with "est_" the same as the existing "est_entries" field. I'm
unsure why MemoizePath.calls becomes Memoize.lookups. Seems
unnecessary and just means more brain space being used to maintain a
mental model.

David