> On Sun, Oct 05, 2003 at 12:14:24PM +0100, Matt Clark wrote: > > more info on how it clobbers shared_buffers? > > Vacuum is like a seqscan. It touches everything on a table. So it > doesn't clobber them, but that's the latest data. It's unlikely your > buffers are big enough to hold your database, unless your database is > small. So you'll end up expiring potentially useful data in the > buffer.
OK I'm definitely missing something here. I thought that the FSM was there to keep track of potentially free pages, and that all VACUUM did was double check and then write that info out for all to see? The promise being that a VACUUM FULL will walk all pages on disk and do a soft-shoe-shuffle to aggresively recover space, but a simple VACUUM won't (merely confirming pages as available for reuse). As for buffers, my understanding is that they are *not* meant to be big enough to hold the DB, as PG explicitly leaves caching up to the underlying OS. 'buffers' here meaning shared memory between PG processes, and 'cache' meaning OS cache. 'buffers' only need to be big enough to hold the intermediate calcs and the results for any current transactions? M ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
