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

On 2023-Feb-15, Dean Rasheed wrote:

> 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.

Thank you, I have pushed it.

> > (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.

Hmm. I wonder if this is just an inconsistency, or rather an outright
bug.

--
Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/