On 2014-10-24 15:59:30 +0530, Amit Kapila wrote: > > > and w.r.t performance it can lead extra > > > function call, few checks and I think in some cases even can > > > acquire/release spinlock. > > > > I fail to see how that could be the case. > > Won't it happen incase first backend sets releaseOK to true and another > backend which tries to wakeup waiters on lock will acquire spinlock > and tries to release the waiters.
Sure, that can happen. > > And again, this is code that's > > only executed around a couple syscalls. And the cacheline will be > > touched around there *anyway*. > > Sure, but I think syscalls are required in case we need to wake any > waiter. It won't wake up a waiter if there's none on the list. > > > > And it'd be a pretty pointless > > > > behaviour, leading to useless increased contention. The only time it'd > > > > make sense for X to be woken up is when it gets run faster than the S > > > > processes. > > > > > > Do we get any major benefit by changing the logic of waking up waiters? > > > > Yes. > > I think one downside I could see of new strategy is that the chance of > Exclusive waiter to take more time before getting woked up is increased > as now it will by pass Exclusive waiters in queue. Note that that *already* happens for any *new* shared locker that comes in. It doesn't really make sense to have share lockers queued behind the exclusive locker if others just go in front of it anyway. > > > Code is more readable, but I don't understand why you > > > want to do refactoring as part of this patch which ideally > > > doesn't get any benefit from the same. > > > > I did it first without. But there's required stuff like > > LWLockDequeueSelf(). And I had several bugs because of the list stuff. > > > > And I did separate the conversion into a separate patch? > > Yeah, but the main patch for wait free LW_SHARED also uses > it. Well, the only thing that it could have done given that the other patch is a preqrequisite is reverting the behaviour? Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers