From: Jeff Davis <pgsql@j-davis.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Is this a problem in GenericXLogFinish()?
Date: Wed, 27 Sep 2023 08:03:45 -0700
Message-ID: <08b4f1f7dcf321d38373f06acc65a8d62cc2f017.camel@j-davis.com> (raw)
In-Reply-To: <CA+TgmobvdZMWj5=fextXP_Q81eS9g0sbVbVE4qiKAtJs8dMjyA@mail.gmail.com>
References: <d2c31606e6bb9b83a02ed4835d65191b38d4ba12.camel@j-davis.com>
<25104133-7df8-cae3-b9a2-1c0aaa1c094a@iki.fi>
<399492009193fa2c37a61b630e4449546a550039.camel@j-davis.com>
<c84114f8-c7f1-5b57-f85a-3adc31e1a904@iki.fi>
<146426fc662f88604c700a72a3833b1919922f9e.camel@j-davis.com>
<CA+TgmobvdZMWj5=fextXP_Q81eS9g0sbVbVE4qiKAtJs8dMjyA@mail.gmail.com>
On Wed, 2023-09-27 at 10:36 -0400, Robert Haas wrote:
> On Tue, Sep 26, 2023 at 9:36 PM Jeff Davis <pgsql@j-davis.com> wrote:
> > That site is pretty trivial to fix, but there are also a couple
> > places
> > in hash.c and hashovfl.c that are registering a clean page and it's
> > not
> > clear to me exactly what's going on.
>
> Huh, I wonder if that's just a bug. Do you know where exactly?
hashovfl.c:665 and hash.c:831
In both cases it's registering the bucket_buf, and has a comment like:
/*
* bucket buffer needs to be registered to ensure that we can
* acquire a cleanup lock on it during replay.
*/
And various redo routines have comments like:
/*
* Ensure we have a cleanup lock on primary bucket page before we
start
* with the actual replay operation. This is to ensure that neither a
* scan can start nor a scan can be already-in-progress during the
replay
* of this operation. If we allow scans during this operation, then
they
* can miss some records or show the same record multiple times.
*/
So it looks like it's intentionally registering a clean buffer so that
it can take a cleanup lock for reasons other than cleaning (or even
modiying) the page. I would think that there's a better way of
accomplishing that goal, so perhaps we can fix that?
Regards,
Jeff Davis
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To: pgsql-hackers@postgresql.org
Cc: pgsql@j-davis.com, robertmhaas@gmail.com, hlinnaka@iki.fi
Subject: Re: Is this a problem in GenericXLogFinish()?
In-Reply-To: <08b4f1f7dcf321d38373f06acc65a8d62cc2f017.camel@j-davis.com>
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