Horton

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

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrew Dunstan <andrew@dunslane.net>, Richard Guo <guofenglinux@gmail.com>, jian he <jian.universality@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-05-07T22:47:32Z
Lists: pgsql-hackers 
On Wed, 8 May 2024 at 10:40, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> David Rowley <dgrowleyml@gmail.com> writes:
> > 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?

REALLOCATE_BITMAPSETS was invented for this and IMO, it found exactly
the problem it was invented to find.

Copy-on-modify is our policy for node mutation. Why is it ok there but
awfully fragile here?

David

Commits

  1. Make left-join removal safe under -DREALLOCATE_BITMAPSETS.

  2. Revert: Remove useless self-joins

  3. Remove mention of nchar