Horton

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

Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>

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From: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
To: David Rowley <dgrowleyml@gmail.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>
Date: 2025-05-01T12:22:34Z
Lists: pgsql-hackers

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On 27.04.2025 22:58, Ilia Evdokimov wrote:
> Therefore, I think it is better to report percentages directly. Since 
> non-text EXPLAIN formats do not display units, I propose to rename the 
> field to "hit_percent" in all formats, including the text format. This 
> way, the meaning of the value remains clear without needing additional 
> context. What do you think about this approach?


I attached updated v9 patch with the suggested changes. The updated line 
in the EXPLAIN looks like this:

Text format:
     Estimates: capacity=1 distinct keys=1 lookups=2 hit percent=50.00%

Non-text format:
     Estimated Capacity: 1
     Estimated Distinct Lookup Keys: 1
     Estimated Lookups: 2
     Estimated Hit Percent: 50.00

Any suggestions?

--
Best regards,
Ilia Evdokimov,
Tantor Labs LLC.