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

From: Andrei Lepikhov <lepihov(at)gmail(dot)com>
To: Ilia Evdokimov <ilya(dot)evdokimov(at)tantorlabs(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Lukas Fittl <lukas(at)fittl(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Nikolay Samokhvalov <samokhvalov(at)gmail(dot)com>
Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost adjustment
Date: 2025-05-01 13:37:52
Message-ID: 8e9f46ce-e087-4dd5-b0c2-4459170da11f@gmail.com
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On 5/1/25 14:22, Ilia Evdokimov wrote:
>     Estimated Hit Percent: 50.00
>
> Any suggestions?
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%.

--
regards, Andrei Lepikhov

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