Re: Revised Patch to allow multiple table locks in "Unison"

Bruce Momjian wrote:
>
> > It seems to me that we already have a small sleep in place. After all, in
> > order to acquite a lock, the shared memory area has to be accessed. So,
> > the contenders for a lock both have to go through a spin lock. So, if we
> > have the two "stuck" processes as in Tom's example, one will win at
> > acquiring the spin lock and the other will have to wait. So, they become
> > desynchronized, regardless of how many CPUs or what memory architecture
> > you have.
>
> I see your point now, that they can't synchronize because they have to
> go through the same semaphore and therefore get out of sync. Do they
> get out of sync enough for one to get the lock while the other is not
> holding it, or do the locks actually keep them in sync? I don't know
> the answer.
>

That is a good point. With the current random sleeps it helps breaking
the
lockstep of the two processes, but when it is changed to a queue the
random
sleeps won't be there anymore.

--
Fernando Nasser
Red Hat Canada Ltd. E-Mail: fnasser(at)redhat(dot)com
2323 Yonge Street, Suite #300
Toronto, Ontario M4P 2C9