From: Tom Lane <tgl@sss.pgh.pa.us>
To: John Naylor <john.naylor@enterprisedb.com>
cc: Robert Haas <robertmhaas@gmail.com>,
        Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
        Justin Pryzby <pryzby@telsasoft.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
        Thomas Munro <thomas.munro@gmail.com>
Subject: Re: pg15b1: FailedAssertion("val > base",
 File: "...src/include/utils/relptr.h", Line: 67, PID: 30485)
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Comments: In-reply-to John Naylor <john.naylor@enterprisedb.com>
	message dated "Wed, 22 Jun 2022 09:49:50 +0700"
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Date: Tue, 21 Jun 2022 22:54:47 -0400
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John Naylor <john.naylor@enterprisedb.com> writes:
> On Wed, Jun 1, 2022 at 2:57 AM Robert Haas <robertmhaas@gmail.com> wrote:
>> ... So we can fix this by:
>> 1. Using a relative pointer value other than 0 to represent a null
>> pointer. Andres suggested (Size) -1.
>> 2. Not storing the free page manager for the DSM in the main shared
>> memory segment at byte offset 0.

> For this open item, the above two ideas were discussed as a short-term
> fix, and my reading of the thread is that the other proposals are too
> invasive at this point in the cycle. Both of them have a draft patch
> in the thread. #2, i.e. wasting MAXALIGN of space, seems the simplest
> and most localized. Any thoughts on pulling the trigger on either of
> these two approaches?

I'm still of the opinion that 0 == NULL is a good property to have,
so I vote for #2.

			regards, tom lane