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.
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Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Wed, 08 May 2024 10:35:42 +1200"
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Date: Tue, 07 May 2024 18:40:16 -0400
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David Rowley <dgrowleyml@gmail.com> writes:
> On Wed, 8 May 2024 at 06:20, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I find that Richard's proposed fix makes the core regression tests
>> pass, but we still fail check-world.  So I'm afraid we need something
>> more aggressive, like the attached which makes make_restrictinfo
>> copy all its input bitmapsets.  Without that, we still have sharing
>> of bitmapsets across different RestrictInfos, which seems pretty
>> scary given what we now see about the effects of 00b41463c.  This
>> seems annoyingly expensive, but maybe there's little choice?

> We could make the policy copy-on-modify.  If you put bms_copy around
> the bms_del_member() calls in remove_rel_from_query(), does it pass
> then?

Didn't test, but that route seems awfully invasive and fragile: how
will we find all the places to modify, or ensure that the policy
is followed by future patches?

			regards, tom lane