If a lock is successfully obtained on one table, but not on all tables, it releases that lock and will retry to get them as a group in the future. Since inheritance acts as a group of tables (top + recursive cascade to children), this implementation is necessary even if only a single table is specified in the command.
I'd prefer to see this as a lock wait mode where it sits in the normal lock queue BUT other lock requestors are allowed to queue jump past it. That should be just a few lines changed in the lock conflict checker and some sleight of hand in the lock queue code.
That way we avoid the busy-wait loop and multiple DEFERRABLE lock waiters queue up normally.
Yeah, that would be better. I can see how to handle a single structure in that way but I'm not at all certain how to handle multiple tables and inheritance is multiple tables even with a single command.
X1 inherits from X
There is a long-running task on X1.
Someone requests LOCK TABLE X IN ACCESS EXCLUSIVE MODE WAIT PATIENTLY. Internally this also grabs X1.
The lock on X might be granted immediately and now blocks all other access to that table.
There would need be a Locking Group kind of thing so various LockTags are treated as a single entity to grant them simultaneously. That seems pretty invasive; at least I don't see anything like that today.
