From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
cc: Matthias van de Meent <boekewurm+postgres@gmail.com>,
        David Rowley <dgrowleyml@gmail.com>,
        PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Add bump memory context type and use it for tuplesorts
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Comments: In-reply-to Tomas Vondra <tomas.vondra@enterprisedb.com>
	message dated "Sat, 17 Feb 2024 01:31:07 +0100"
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Date: Fri, 16 Feb 2024 20:10:48 -0500
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Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> On 2/17/24 00:14, Tom Lane wrote:
>> The conclusion was that the specific invalid values didn't matter as
>> much on the other platforms as they do with glibc.  But right now you
>> have a fifty-fifty chance that a pointer to garbage will look valid.
>> Do we want to increase those odds?

> Not sure. The ability to detect bogus pointers seems valuable, but is
> the difference between 4/8 and 3/8 really qualitatively different? If it
> is, maybe we should try to increase it by simply adding a bit.

I think it'd be worth taking a fresh look at the bit allocation in the
header word to see if we can squeeze another bit without too much
pain.  There's basically no remaining headroom in the current design,
and it starts to seem like we want some.  (I'm also wondering whether
the palloc_aligned stuff should have been done some other way than
by consuming a context type ID.)

			regards, tom lane