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help / color / mirror / Atom feedFrom: David Rowley <[email protected]>
To: Ilia Evdokimov <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Lukas Fittl <[email protected]>
Cc: Daniel Gustafsson <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Nikolay Samokhvalov <[email protected]>
Cc: Andrei Lepikhov <[email protected]>
Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost adjustment
Date: Fri, 18 Apr 2025 09:29:37 +1200
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On Wed, 16 Apr 2025 at 10:09, Ilia Evdokimov
<[email protected]> 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
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Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost adjustment
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