Message-ID: <14a42b49-f733-41ba-9cde-8669984116e6@tantorlabs.com>
Date: Thu, 1 May 2025 22:10:56 +0300
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost
 adjustment
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>
References: <CAP53Pky29GWAVVk3oBgKBDqhND0BRBN6yTPeguV_qSivFL5N_g@mail.gmail.com>
 <81ef0f5a-b6a1-4417-ae3a-2bae9b8d419e@gmail.com>
 <67b5c84a-dedd-4103-af7e-0117046102fe@tantorlabs.com>
 <580fe72c-85be-45a8-9e00-6b5417690557@tantorlabs.com>
 <CAApHDvpT0Y1BfYgeWz+PkKaLBEff1izYOAjNSibhBTNFEdqLtg@mail.gmail.com>
 <CA+TgmobDHmaNTqi5yLPJoW6fTCuiWOgF9CSCSHX_OTLmGxYRUQ@mail.gmail.com>
 <CAApHDvqYL3OVvOsyvEPsDJ7h4zQh=LEygQgcQSN-TemRJLMb6Q@mail.gmail.com>
 <3ea66a50-e4b0-4f20-ae0c-4d9cbaf81cfb@tantorlabs.com>
 <CAApHDvpuM8jW-BGu7B=i6uv+jmndEo-2z_BYvj5JNmx=qV-uSQ@mail.gmail.com>
 <0e8dc4fa-3655-4e9f-9424-9b32a15e6acd@tantorlabs.com>
 <CAApHDvqmyHuEt7rdFLJr4cZecbhno5OZ6iL5EQNNu9Oi1f93sQ@mail.gmail.com>
 <7e995158-157e-4ec6-a7c8-266c1a6f7b43@tantorlabs.com>
 <CAApHDvq0Zz3+nh9hPRBP-oAocFZETfhdE_jcN8aG+Thc24Zk5g@mail.gmail.com>
 <06840539-e321-4930-9f89-cfc783c5b80a@tantorlabs.com>
 <15e0422a-31ec-4e82-b0cf-0839f636b185@tantorlabs.com>
 <8e9f46ce-e087-4dd5-b0c2-4459170da11f@gmail.com>
Content-Language: en-US
From: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
In-Reply-To: <8e9f46ce-e087-4dd5-b0c2-4459170da11f@gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: <https://www.postgresql.org/message-id/14a42b49-f733-41ba-9cde-8669984116e6%40tantorlabs.com>
Precedence: bulk


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.