deadlock avoidance
I noticed the following in some of our code today:
select ... <join list> ... for update of a, b;
Inasmuch as the cardinal rule for avoiding deadlocks is to acquire
locks in a consistent order, should such a construction be avoided
in favor of two separate "select ... for update" statements so that
the order of acquisition of a and b is known? I'm assuming that
there is no ordering implied/guaranteed by "for update of a, b".
Or am I missing something?
Clarence
Clarence Gardner <clarence@silcom.com> writes:
I noticed the following in some of our code today:
select ... <join list> ... for update of a, b;
Inasmuch as the cardinal rule for avoiding deadlocks is to acquire
locks in a consistent order, should such a construction be avoided
in favor of two separate "select ... for update" statements so that
the order of acquisition of a and b is known?
If you're worried about deadlock, what you should be worrying about is
the order in which the individual rows are visited --- and splitting
this into two SQL commands doesn't in itself guarantee more about that
than the command as given.
regards, tom lane