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: Andrei Lepikhov <lepihov@gmail.com>, 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>
Date: 2025-05-01T19:10:56Z
Lists: pgsql-hackers 
On 01.05.2025 16:37, Andrei Lepikhov wrote:
> I still think that two meaningful digits are enough for an EXPLAIN. We 
> usually need to estimate the tuple set's size, not a precise number of 
> tuples or groups. And definitely, not an arbitrarily chosen two digits 
> after the point. So, IMO, good examples may look like the following:
> 50%, 5.0%, 0.00051%.
>

The idea is not bad. But I think it might be better to raise this in a 
new thread, because this is not the only place [0] where we might want 
to output numbers like that. We could also discuss there what else might 
benefit from such formatting.

[0]: 
https://www.postgresql.org/message-id/3365160.1739385615%40sss.pgh.pa.us

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