Tom Lane wrote: > Magnus Hagander <[EMAIL PROTECTED]> writes: >> Tom Lane wrote: >>> How is it possible for a semaphore to be unlocked "too many times"? >>> It's supposed to be a running counter of the net V's minus P's, and >>> yes it had better be able to count higher than one. Have we chosen >>> the wrong Windows primitive to implement this? > >> No, it's definitly the right primitive. But we're creating it with a max >> count of 1. > > That's definitely wrong. There are at least three reasons for a PG > process's semaphore to be signaled (heavyweight lock release, LWLock > release, pin count waiter), and at least two of them can occur > concurrently (eg, if deadlock checker fires, it will need to take > LWLocks, but there's nothing saying that the original lock won't be > released while it waits for an LWLock). > > The effective max count on Unixen is typically in the thousands, > and I'd suggest the same on Windows unless there's some efficiency > reason to keep it small (in which case, maybe ten would do).
AFAIK there's no problem with huge numbers (it takes an int32, and the documentation says nothing about a limit - I'm sure it's just a 32-bit counter in the kernel). I'll give that a shot. Marcin - can you test a source patch? Or should I try to build you a binary for testing? It'd be good if you can confirm that it works before we commit anything, I think. > I'm astonished that we've not seen this reported before. Has the > Windows sema code always been like that? It could be an 8.2 problem, actually, since we had new semaphore code there. Looking at http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/port/win32/Attic/sema.c?rev=1.13;content-type=text%2Fx-cvsweb-markup, it looks like we may have used a *semaphore* with just one as top, but then kept a counter in userspace as well... (Haven't looked through the details of the code, but it looks that way from a casual view) //Magnus ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
