Re: deadlock avoidance

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

Clarence Gardner <clarence(at)silcom(dot)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