Re: BUG #17792: MERGE uses uninitialized pointer and crashes when target tuple is updated concurrently - Mailing list pgsql-bugs

From Dean Rasheed
Subject Re: BUG #17792: MERGE uses uninitialized pointer and crashes when target tuple is updated concurrently
Date
Msg-id CAEZATCWTFjn6rCx3=NCQhVaRZyi-w=jj8OEmJx9Fb_em5dh4Ew@mail.gmail.com
Whole thread Raw
In response to Re: BUG #17792: MERGE uses uninitialized pointer and crashes when target tuple is updated concurrently  (Alvaro Herrera <alvherre@alvh.no-ip.org>)
Responses Re: BUG #17792: MERGE uses uninitialized pointer and crashes when target tuple is updated concurrently  (Alvaro Herrera <alvherre@alvh.no-ip.org>)
List pgsql-bugs
On Tue, 14 Feb 2023 at 19:19, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> I agree, this looks to be a good fix.  However, I couldn't in a quick
> try reproduce the problem, so I haven't been able to verify it.  I'll
> try to do that early tomorrow.
>

I did some more testing, and the fix looks good.

> (I also delete the XXX comment there.)
>

That makes sense. It's a bit inconsistent (though not related to this
bug) that a cross-partition update will return OK if the tuple was
concurrently deleted, so merge will think that it updated the tuple
and not try an insert action, whereas for a normal update it will try
an insert action if the tuple was concurrently deleted. The thing that
seems wrong there is that ExecUpdateAct() sets updateCxt->updated =
true for a cross-partition update regardless of whether it actually
executed the insert half of the update/move. In theory, that flag
could be set to false so that merge would know if the tuple was
concurrently deleted, though it's not clear if it's worth it.

Regards,
Dean



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