From: Tom Lane <tgl@sss.pgh.pa.us>
To: Heikki Linnakangas <hlinnaka@iki.fi>
cc: Alvaro Herrera <alvherre@alvh.no-ip.org>,
        Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>,
        Maxim Orlov <orlovmg@gmail.com>,
        Alexander Korotkov <aekorotkov@gmail.com>,
        wenhui qiu <qiuwenhuifx@gmail.com>,
        Postgres hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: POC: make mxidoff 64 bits
In-reply-to: <2d9282d3-7f24-4e1c-af5f-cd33316dead7@iki.fi>
References: <202512110804.hmukvd7jna34@alvherre.pgsql>
 <2d9282d3-7f24-4e1c-af5f-cd33316dead7@iki.fi>
Comments: In-reply-to Heikki Linnakangas <hlinnaka@iki.fi>
	message dated "Fri, 12 Dec 2025 10:51:25 +0200"
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Date: Sun, 14 Dec 2025 17:55:36 -0500
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Heikki Linnakangas <hlinnaka@iki.fi> writes:
> Ok, I have pushed this. Thanks!

Coverity is unhappy about this bit:

/srv/coverity/git/pgsql-git/postgresql/src/bin/pg_upgrade/multixact_read_v=
18.c: 282             in GetOldMultiXactIdSingleMember()
276             if (!TransactionIdIsValid(*xactptr))
277             {
278                 /*
279                  * Corner case 2: we are looking at unused slot zero
280                  */
281                 if (offset =3D=3D 0)
>>>     CID 1676077:         Control flow issues  (DEADCODE)
>>>     Execution cannot reach this statement: "continue;".
282                     continue;
283     =

284                 /*
285                  * Otherwise this is an invalid entry that should not =
be

It sees the earlier test for offset =3D=3D 0, and evidently is assuming
that the loop's "offset++" will not wrap around.  Now I think that
the point of this check is exactly that "offset++" could have wrapped
around, but the commentary is not so clear that I'm certain this is a
false positive.  If that is the intention, what do you think of
rephrasing this comment as "we have wrapped around to unused slot
zero"?

			regards, tom lane