Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost adjustment

On Wed, 16 Apr 2025 at 10:09, Ilia Evdokimov
<ilya(dot)evdokimov(at)tantorlabs(dot)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