Paul Jungwirth <pj@illuminatedcomputing.com> writes:
> I noticed that Postgres takes an AccessExclusiveLock (a lock on the
> whole table) against the *referenced* table when dropping a foreign key.
Yeah, that's because it involves removing a trigger.
Adding a trigger used to require AEL as well, but it was successfully
argued that that end of things could use a weaker lock. I find the
reasoning rather dubious myself.
regards, tom lane