>The disk cache on most operating systems is optimized. Plus, keeping shared buffers low gives you more room to bump up the sort memory, which will make your big queries run faster.
Thanks merlin, Whether the OS caches the data or PG does, you still want it cached. If your sorting backends gobble up the pages that otherwise would be filled with the database buffers, then your postmaster will crawl, as it'll *really* have to wait for stuff from disk. In my scenario, you'd spec the machine so that there would be plenty of memory for *everything*. On your OS optimisation point, OS caches are, of course, optimised. But people have told me that PG's caching strategy is simply less well optimised, and *that* is the reason for keeping the shared buffer cache down in my scenario. That's a shame in a way, but I understand why it is the way it is - other things have been addressed which speed up operations in different ways. My 'all in RAM' scenario is very rare at the moment, so why waste valuable development resources on developing optimised RAM based data structures to hold the data for quicker query execution when hardly anyone will see the benefit? However - it won't be so rare for too much longer... If I gave you a half a terabyte of RAM and a 4 processor 64 bit machine, I'm sure you could imagine how much quicker databases could run if they were optimised for this sort of platform. Anyway, I'm looking forward to experimenting with stuff the way it works at the moment. Many thanks, Andy ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org