Re: BUG #17792: MERGE uses uninitialized pointer and crashes when target tuple is updated concurrently

On Tue, 14 Feb 2023 at 19:19, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)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