Lance, > I have a PostgreSQL database that runs on a dedicated server. The > server has 24Gig of memory. What would be the max size I would ever > want to set the shared_buffers to if I where to relying on the OS for > disk caching approach? It seems that no matter how big your dedicated > server is there would be a top limit to the size of shared_buffers.
There's not, actually. Under some circumstances (mainly Solaris 10 + UFS on AMD) it can actually be beneficial to have s_b be 80% of RAM and bypass the FS cache entirely. This isn't usually the case, but it's not to be ruled out. If you're relying on the FS cache and not using direct I/O, though, you want to keep at least 50% of memory free for use by the cache. At below 50%, you lose a significant part of the benefit of the cache without losing the cost of it. Of course, that assumes that your database is bigger than ram; there isn't much need to have either s_b or the f.s.c. be more than twice the size of your whole database. In general, a setting s_b to 25% of RAM on a dedicated machine, and 10% (with a max of 512MB) on a shared machine, is a nice safe default which will do OK for most applications. -- --Josh Josh Berkus PostgreSQL @ Sun San Francisco ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
