| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Cc: | "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Subject: | Re: Fix bank selection logic in SLRU |
| Date: | 2024-12-10 14:00:07 |
| Message-ID: | CA+TgmobsdBxApp7EK61Y_81G3dYHN9-M+6PmKz+pU51y58TMpg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Dec 10, 2024 at 8:58 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>> Bank selection code assumes that number of buffers is power of 2.
>> If the number of buffers is not power of 2 - only subset of buffers will be used. In worst case, e.g. 65 buffers, everything will be buffered only in bank 64.
>
> But why that would be the case? the acceptable values for GUC to configure the slru buffers are in multiple of 16(bank size) we have that check to check the GUC values.
"Must be a multiple of 16" and "must be a power of 2" are different
criteria. For example, 48 is a multiple of 16 but it is not a power of
2. If the code assumes that we have an actual power of 2, the check
you quoted in your previous email is insufficient.
--
Robert Haas
EDB: http://www.enterprisedb.com
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