Re: Lock conflict behavior?

Tatsuo Ishii  writes:
> I'm wondering if following behavior of PostgreSQL regarding lock
> conflict is an expected one. Here's a scenario:

> Session A:
> 	BEGIN;
> 	SELECT * FROM  pg_class limit 1; -- acquires access share lock

> Session B:
> 	BEGIN;
> 	ALTER TABLE pg_class ....;	-- waits for acquiring access
> 					   exclusive lock(wil fail anyway though)
> Session C:
> 	SELECT * FROM pg_class...;	-- whatever query which needs
> 					   to acces pg_class will be
> 					   blocked, too bad...

> I understand that B should wait for aquiring lock, but Should C wait
> for?

If we didn't do this, then a would-be acquirer of exclusive lock would
have a very serious problem with lock starvation: it might wait forever
in the face of a continuous stream of access-share lock requests.
		regards, tom lane