On Friday 19 November 2010 15:58:39 Aidan Van Dyk wrote: > On Fri, Nov 19, 2010 at 9:49 AM, Andres Freund <and...@anarazel.de> wrote: > > Well, its not generally true - you are right there. But there is a wide > > range for syscalls available where its inherently true (which is what I > > sloppily referred to). And you are allowed to call a, although quite > > restricted, set of system calls even in signal handlers. I don't have > > the list for older posix versions in mind, but for 2003 you can choose > > something from several like write, lseek,setpgid which inherently have > > to serialize. And I am quite sure there were sensible calls for earlier > > versions. > > Well, it's not quite enough just to call into the kernel to serialize > on "some point of memory", because your point is to make sure that > *this particular piece of memory* is coherent. It doesn't matter if > the kernel has proper fencing in it's stuff if the memory it's > guarding is in another cacheline, because that won't *necessarily* > force cache coherency in your local lock/variable memory. Yes and no. It provides the same guarantees as our current approach of using spinlocks for exactly that - that it theoretically is not enough is an independent issue (but *definitely* an issue).
Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
