Feedback-ID: ia2694551:Fastmail
Date: Fri, 17 Nov 2023 14:58:32 +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-17, Dilip Kumar wrote:

> On Thu, Nov 16, 2023 at 3:11 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> >
> > I just noticed that 0003 does some changes to
> > TransactionGroupUpdateXidStatus() that haven't been adequately
> > explained AFAICS.  How do you know that these changes are safe?
> 
> IMHO this is safe as well as logical to do w.r.t. performance.  It's
> safe because whenever we are updating any page in a group we are
> acquiring the respective bank lock in exclusive mode and in extreme
> cases if there are pages from different banks then we do switch the
> lock as well before updating the pages from different groups.

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?


I think in the code comments where you use "w.r.t.", that acronym can be
replaced with "for", which improves readability.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"All rings of power are equal,
But some rings of power are more equal than others."
                                 (George Orwell's The Lord of the Rings)