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

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От Richard Guo
Тема Re: Revert: Remove useless self-joins *and* -DREALLOCATE_BITMAPSETS make server crash, regress test fail.
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Msg-id CAMbWs49skj4LBP4QQe5Pt31JadC4Z1p38s=GySkO+Jdn6PYWnQ@mail.gmail.com
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Ответ на Re: Revert: Remove useless self-joins *and* -DREALLOCATE_BITMAPSETS make server crash, regress test fail.  (David Rowley <dgrowleyml@gmail.com>)
Ответы Re: Revert: Remove useless self-joins *and* -DREALLOCATE_BITMAPSETS make server crash, regress test fail.
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On Tue, May 7, 2024 at 1:46 PM David Rowley <dgrowleyml@gmail.com> wrote:
On Tue, 7 May 2024 at 17:28, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> What I'm trying to figure out here is whether we have a live bug
> in this area in released branches; and if so, why we've not seen
> reports of that.

We could check what portions of REALLOCATE_BITMAPSETS are
backpatchable. It may not be applicable very far back because of v16's
00b41463c. The bms_del_member() would have left a zero set rather than
doing bms_free() prior to that commit.  There could be a bug in v16.

I also think there might be a bug in v16, as long as
'sjinfo->syn_lefthand' and 'rinfo->outer_relids' are referencing the
same bitmapset and the content of this bitmapset is altered through
'sjinfo->syn_lefthand' without 'rinfo->outer_relids' being aware of
these changes.  I tried to compose a query that can trigger this bug but
failed though.

Another thing that comes to my mind is that this issue shows that
RestrictInfo.outer_relids could contain references to removed rels and
joins, and RestrictInfo.outer_relids could be referenced after the
removal of useless left joins.  Currently we do not have a mechanism to
clean out the bits in outer_relids during outer join removal.  That is
to say, RestrictInfo.outer_relids might be referenced while including
rels that should have been removed.  I'm not sure if this is a problem.

Thanks
Richard

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