Re: Bogus assertion in multixact.c?

On Tue, May 03, 2005 at 09:33:30PM +0300, Heikki Linnakangas wrote:
> There's an assertion in multixact.c, MultiXactIdExpand function, line 273:
>
> Assert(!TransactionIdEquals(multi, xid));
>
> where multi is a MultiXactId and xid is a TransactionId.
>
> Isn't this bogus? If I understand the code correctly, multixactids and
> regular xids live in completely separate id spaces. Therefore a comparison
> between them makes no sense.

Well :-) actually that particular MultiXactId may be a TransactionId.
(See the isMulti param, and comments at the beggining of the function.)
This ugliness is there to support the notion of locking a tuple with
either a TransactionId (non-contention case) or a MultiXactId
(concurrent case.)

We require MultiXactId to be equivalent to TransactionId anyway, because
we store Multis on a tuple's Xmax.

Congratulations for spotting that :-) (Are you using a source checker
tool?)

--
Alvaro Herrera (<alvherre[(at)]dcc(dot)uchile(dot)cl>)
"No hay cielo posible sin hundir nuestras raíces
en la profundidad de la tierra" (Malucha Pinto)