On 10/21/06, Martijn van Oosterhout <kleptog@svana.org> wrote:
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.
right, and a small clarification: the above claim of 30% was from using adaptive readahead, not posix_fadvise. posix_fadvise was suggested by none other than andrew morton as the way to get the most i/o out of your box. there was no mention of aio :) merlin ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
