On Tue, 2007-03-13 at 10:08 -0700, Jeff Davis wrote: > On Tue, 2007-03-13 at 12:53 -0400, Tom Lane wrote: > > Jeff Davis <[EMAIL PROTECTED]> writes: > > > I agree that ss_report_loc() doesn't need to report on every call. If > > > there's any significant overhead I agree that it should report less > > > often. Do you think that the overhead is significant on such a simple > > > function? > > > > One extra LWLock cycle per page processed definitely *is* a significant > > overhead ... can you say "context swap storm"? I'd think about doing it > > once every 100 or so pages. > > > > No lock is needed to store the hint. If somehow the hint (which is > stored in a static table, no pointers) gets invalid data due to a race > condition, the new scan will simply consider the hint invalid and start > at 0. > > I did this precisely to avoid causing a performance regression for usage > patterns that don't benefit from sync scans.
Shared memory access is still a performance/scalability concern because so many people want access to it at the same time. There really is no need to do this after each block. 8 CPUs ought to be able to do 8 scans without tripping over each other. Especially if they are on separate tables. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
