On Tue, Dec 17, 2013 at 8:02 AM, Jim Nasby <j...@nasby.net> wrote: > On 12/17/13, 8:34 AM, Robert Haas wrote: > >> On Tue, Dec 17, 2013 at 12:09 AM, Amit Kapila <amit.kapil...@gmail.com> >> wrote: >> >>> I have used pg_prewarm during some of work related to Buffer Management >>> and >>> other performance related work. It is quite useful utility. >>> +1 for reviving this patch for 9.4 >>> >> >> Any other votes? >> > > We've had to manually code something that runs EXPLAIN ANALYZE SELECT * > from a bunch of tables to warm our caches after a restart, but there's > numerous flaws to that approach obviously. > > Unfortunately, what we really need to warm isn't the PG buffers, it's the > FS cache, which I suspect this won't help. But I still see where just > pg_buffers would be useful for a lot of folks, so +1.
Since it doesn't use directIO, you can't warm the PG buffers without also warming FS cache as a side effect. That is why I like 'buffer' as the default--if the data fits in shared_buffers, it warm those, otherwise it at least warms the FS. If you want to only warm the FS cache, you can use either the 'prefetch' or 'read' modes instead. Cheers, Jeff
