On Wed, May 30, 2012 at 10:57 AM, Bruce Momjian <br...@momjian.us> wrote: > On Wed, May 30, 2012 at 10:38:10AM -0700, Jeff Janes wrote: >> On Wed, May 30, 2012 at 9:56 AM, Bruce Momjian <br...@momjian.us> wrote: >> > As part of a blog, I started looking at how a user could measure the >> > pressure on shared buffers, e.g. how much are they being used, recycled, >> > etc. >> > >> > They way you normally do it on older operating systems is to see how >> > many buffers on the free list (about to be reused) are reclaimed as >> > needed --- that usually indicates kernel cache pressure. Unfortunately, >> > we don't have a freelist, except for initial assignment of shared >> > buffers on startup. >> >> Isn't that what the buffers_alloc from pg_stat_bgwriter is ? > > The issue is that once a buffer is removed from the free list, it is > never returned to the free list.
A buffer doesn't need to be removed from the linked list in order for buffers_alloc to get incremented. Conceptually, the freelist consists not only of the linked list, but also of all unpinned buffers with a usagecount of zero. Cheers, Jeff -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
