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From: Tom Lane <[email protected]>
To: Alvaro Herrera <[email protected]>
Cc: [email protected]
Cc: Dilip Kumar <[email protected]>
Subject: Re: pgsql: Improve performance of subsystems on top of SLRU
Date: Sun, 03 Mar 2024 16:14:49 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Alvaro Herrera <[email protected]> writes:
> And I think it's correct that this is somewhat bogus, or at least
> confusing: the only way to have control back here on line 1371 after
> having executed once is via the "goto retry" line below; and there we
> release "prevlock" and set it to NULL beforehand, so it's impossible for
> prevlock to be NULL.  Looking closer I think this code is all confused,
> so I suggest to rework it as shown in the attached patch.

This is certainly simpler, but I notice that it holds the current
LWLock across the line

 	ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember));

where the old code did not.  Could the palloc take long enough that
holding the lock is bad?

Also, with this coding the "lock = NULL;" assignment just before
"goto retry" is a dead store.  Not sure if Coverity or other static
analyzers would whine about that.

			regards, tom lane

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