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In-Reply-To: <11c709e1-9b17-4c00-9ead-93609a09b9db@gmail.com>
From: David Rowley <dgrowleyml@gmail.com>
Date: Tue, 25 Mar 2025 11:05:16 +1300
Message-ID: 
 <CAApHDvr9kjuo0rX03Qm0cDP_tFNJ8crOtpRzbyS0Zwtg2BorRw@mail.gmail.com>
Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost
 adjustment
To: Andrei Lepikhov <lepihov@gmail.com>
Cc: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>,
 Lukas Fittl <lukas@fittl.com>,
	Daniel Gustafsson <daniel@yesql.se>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Nikolay Samokhvalov <samokhvalov@gmail.com>
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On Tue, 25 Mar 2025 at 10:23, Andrei Lepikhov <lepihov@gmail.com> wrote:
>
> On 3/23/25 22:16, David Rowley wrote:
> > Once again, I'm not necessarily objecting to hit and evict ratios
> > being shown, I just want to know they're actually useful enough to
> > show and don't just bloat the EXPLAIN output needlessly. So far your
> > arguments aren't convincing me that they are.

> I'm -1 for this redundancy.

I'm not following what the -1 is for. Is it for showing both hit and
evict ratios?  And your vote is only for adding hit ratio?

Just to make it clear, the evict ratio isn't redundant because we show
hit ratio. If you have 1000 calls and 1000 distinct values and enough
memory to store those, then that's a 0% hit ratio since the first
lookup is a miss. If you change the calls to 2000 then that's a 50%
hit ratio and still 0% evict.

David