Re: Reducing overhead of frequent table locks

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> When a strong lock is taken or released, we have to increment or
> decrement strong_lock_counts[fasthashpartition]. Here's the question:
> is that atomic? In other words, suppose that strong_lock_counts[42]
> starts out at 0, and two backends both do ++strong_lock_counts[42].
> Are we guaranteed to end up with "2" in that memory location or might
> we unluckily end up with "1"? I think the latter is possible... and
> some guard is needed to make sure that doesn't happen.

There are "atomic increment" primitives on most/all multiprocessors,
although availing ourselves of them everywhere will take an amount of
work not unlike developing the spinlock primitives :-(. You are dead
right that this is unsafe without that.

regards, tom lane