Re: Revert: Remove useless self-joins *and* -DREALLOCATE_BITMAPSETS make server crash, regress test fail.

David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> On Wed, 8 May 2024 at 10:55, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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