From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@lists.postgresql.org, Jaime Casanova <jaime.casanova@2ndQuadrant.com>
Subject: Re: LogwrtResult contended spinlock
Date: Mon, 31 Aug 2020 14:34:45 -0400
Message-ID: <20200831183445.GA23447@alvherre.pgsql> (raw)
In-Reply-To: <CE5FB7B4-BD5B-40C1-A915-0AE770812C3D@anarazel.de>
On 2020-Aug-31, Andres Freund wrote:
> Hi,
>
> On August 31, 2020 11:21:56 AM PDT, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> >At first I wanted to make the new LWLock cover only LogwrtResult
> >proper,
> >and leave LogwrtRqst alone. However on doing it, it seemed that that
> >might change the locking protocol in a nontrivial way. So I decided to
> >make it cover both and call it a day. We did verify that the patch
> >solves the reported problem, at any rate.
>
> Wouldn't the better fix here be to allow reading of individual members
> without a lock? E.g. by wrapping each in a 64bit atomic.
Heh, Simon said the same. It's not clear to me due to the lack of
general availability of 64-bit atomics. If they are spinlock-protected
when emulated, I think that would make the problem worse.
IIRC Thomas wanted to start relying on atomic 64-bit vars in some patch,
but I don't remember what it was.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: alvherre@2ndquadrant.com, andres@anarazel.de, jaime.casanova@2ndQuadrant.com
Subject: Re: LogwrtResult contended spinlock
In-Reply-To: <20200831183445.GA23447@alvherre.pgsql>
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