Feedback-ID: ia2694551:Fastmail
Date: Sat, 18 Nov 2023 20:00:04 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: "Andrey M. Borodin" <x4mmm@yandex-team.ru>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: SLRU optimization - configurable buffer pool and partitioning
 the SLRU lock
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On 2023-Nov-18, Dilip Kumar wrote:

> On Fri, Nov 17, 2023 at 6:16 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:

> > I wonder what's the deal with false sharing in the new
> > bank_cur_lru_count array.  Maybe instead of using LWLockPadded for
> > bank_locks, we should have a new struct, with both the LWLock and the
> > LRU counter; then pad *that* to the cacheline size.  This way, both the
> > lwlock and the counter come to the CPU running this code together.
> 
> Actually, the array lengths of both LWLock and the LRU counter are
> different so I don't think we can move them to a common structure.
> The length of the *buffer_locks array is equal to the number of slots,
> the length of the *bank_locks array is Min (number_of_banks, 128), and
> the length of the *bank_cur_lru_count array is number_of_banks.

Oh.

> > Looking at the coverage for this code,
> > https://coverage.postgresql.org/src/backend/access/transam/clog.c.gcov.html#413
> > it seems in our test suites we never hit the case where there is
> > anything in the "nextidx" field for commit groups.  To be honest, I
> > don't understand this group stuff, and so I'm doubly hesitant to go
> > without any testing here.  Maybe it'd be possible to use Michael
> > Paquier's injection points somehow?
> 
> Sorry, but I am not aware of "Michael Paquier's injection" Is it
> something already in the repo? Can you redirect me to some of the
> example test cases if we already have them? Then I will try it out.

https://postgr.es/ZVWufO_YKzTJHEHW@paquier.xyz

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"Sallah, I said NO camels! That's FIVE camels; can't you count?"
(Indiana Jones)