Re: not null constraints, again

Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> On 2025-Apr-14, Tom Lane wrote:
>> I would not have expected that adding pg_constraint rows implies
>> stronger locks than what ALTER ADD PRIMARY KEY was using before,
>> and I suspect that doing so will cause more problems than just
>> breaking parallel restore.

> I wasn't aware of this side effect.  I'll investigate this in more
> depth.  I suspect it might be a bug in the way we run through ALTER
> TABLE for the primary key.

After further thought it occurs to me that it might not be a case
of "we get stronger locks", but a case of "we accidentally get a
weaker lock earlier and then try to upgrade it", thus creating a
possibility of deadlock where before we'd just have blocked till
the other statement cleared.  Still worthy of being fixed if that's
true, though.

            regards, tom lane