Re: Proper Method for using LockAcquire

Chris Bowlby <excalibur(at)accesswave(dot)ca> writes:
> I've been working on a small module that I will be pluging into my
> local PostreSQL 8.x database and am in need of doing some table locking.
> At this time, I've used various other examples to no avail and was
> wondering what the proper method for aquiring a table lock within the
> module would be?

You should not be touching locks at any level lower than lmgr.c's
exports; eg LockRelation() not LockAcquire(). The LockAcquire API
is not as stable.

Usually people take a relation lock in combination with opening the rel
in the first place, ie, specify the desired lock to heap_open or
relation_open or one of their variants. If you apply LockRelation() to
an already-opened rel then you need to be worrying about possible
deadlocks due to lock upgrading.

Also, 90% of the time you probably don't want to release the lock
explicitly at all; leave it to be held until transaction end.
Early release violates the 2PL principle, so you need to analyze
things pretty carefully to determine if it's safe.

regards, tom lane