Re: locks in CREATE TRIGGER, ADD FK

Neil Conway <neilc@samurai.com> writes: 
>       /*
> !      * Grab an exclusive lock on the pk table, so that someone doesn't
> !      * delete rows out from under us. (Although a lesser lock would do for
> !      * that purpose, we'll need exclusive lock anyway to add triggers to
> !      * the pk table; trying to start with a lesser lock will just create a
> !      * risk of deadlock.)
>        */
> !     pkrel = heap_openrv(fkconstraint->pktable, AccessExclusiveLock); 
>       /*
>        * Validity and permissions checks
> --- 3829,3839 ----
>       Oid            constrOid; 
>       /*
> !      * Grab a lock on the pk table, so that someone doesn't delete
> !      * rows out from under us; ShareRowExclusive should be good
> !      * enough.
>        */


BTW, the above comment change is seriously inadequate, because it
removes the explanation of *why* that is the minimum required lock.
        regards, tom lane