From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: Andrew Dunstan <andrew@dunslane.net>, Richard Guo <guofenglinux@gmail.com>,
        jian he <jian.universality@gmail.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Revert: Remove useless self-joins *and* -DREALLOCATE_BITMAPSETS make server crash, regress test fail.
In-reply-to: <CAApHDvqRgYq8yL3GUj-1z2xPv6cLy7D4tjxhhijWnsHLOSukLg@mail.gmail.com>
References: <CACJufxFVQmr4=JWHAOSLuKA5Zy9H26nY6tVrRFBOekHoALyCkQ@mail.gmail.com> <CAApHDvpBMSGhXVeFdw_qmjPqU5yHvJJ7k0z7kD069EC4di2Pag@mail.gmail.com> <CAMbWs4-iYKxrMs8kj+49gVA4X1_=PYAaw5HL_3g_yVXpAHzYww@mail.gmail.com> <1e6ca7b3-98e6-46b2-9982-97f92c7523d8@dunslane.net> <76910.1715106055@sss.pgh.pa.us> <CAApHDvoR9cXHb_+j7j8=zBty35B8z22SX51cZN7ZRf+QTPJ1fA@mail.gmail.com> <276516.1715121616@sss.pgh.pa.us> <CAApHDvrvcJd2DCAV0vDKmRxp5tvXq3=+RwhRns4OjoHQ1UbDEg@mail.gmail.com> <279607.1715122556@sss.pgh.pa.us> <CAApHDvqRgYq8yL3GUj-1z2xPv6cLy7D4tjxhhijWnsHLOSukLg@mail.gmail.com>
Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Wed, 08 May 2024 11:03:16 +1200"
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Date: Tue, 07 May 2024 19:18:09 -0400
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David Rowley <dgrowleyml@gmail.com> writes:
> On Wed, 8 May 2024 at 10:55, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Not in a way that gives me any confidence that we found *all* the
>> problems.

> Here are some statements I believe to be true:
> 1. If REALLOCATE_BITMAPSETS is defined then modifications to a
> Bitmapset will make a copy and free the original.
> 2. If a query runs successfully without REALLOCATE_BITMAPSETS and
> Assert fails due to an invalid Bitmapset when REALLOCATE_BITMAPSETS is
> defined, then we have > 1 pointer pointing to the same set and not all
> of them are being updated when the members are added/removed.

> Given the above, I can't see what Bitmapset sharing problems we won't
> find with REALLOCATE_BITMAPSETS.

Anything where the trouble spots are in a code path we fail to
exercise with our available test suites.  If you think there are
no such code paths, I'm sorry to disillusion you.

I spent a little bit of time wondering if we could find problems in a
more static way by marking bitmapset fields as "const", but I fear
that would create a huge number of false positives.

			regards, tom lane