Martijn van Oosterhout wrote: -- Start of PGP signed section. > On Fri, Oct 20, 2006 at 03:04:55PM -0400, Merlin Moncure wrote: > > On 10/20/06, Tom Lane <[EMAIL PROTECTED]> wrote: > > >So far I've seen no evidence that async I/O would help us, only a lot > > >of wishful thinking. > > > > is this thread moot? while researching this thread I came across this > > article: http://kerneltrap.org/node/6642 describing claims of 30% > > performance boost when using posix_fadvise to ask the o/s to prefetch > > data. istm that this kind of improvement is in line with what aio can > > provide, and posix_fadvise is cleaner, not requiring threads and such. > > Hmm, my man page says: > > POSIX_FADV_WILLNEED and POSIX_FADV_NOREUSE both initiate a > non-blocking read of the specified region into the page cache. > The amount of data read may be decreased by the kernel depending > on VM load. (A few megabytes will usually be fully satisfied, > and more is rarely useful.) > > This appears to be exactly what we want, no? It would be nice to get > some idea of what systems support this.
See our xlog.c for our experience in trying to use it: /* * posix_fadvise is problematic on many platforms: on older x86 Linux it * just dumps core, and there are reports of problems on PPC platforms as * well. The following is therefore disabled for the time being. We could * consider some kind of configure test to see if it's safe to use, but * since we lack hard evidence that there's any useful performance gain to * be had, spending time on that seems unprofitable for now. */ -- Bruce Momjian [EMAIL PROTECTED] EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq