Re: Figuring out shared buffer pressure

On Wed, May 30, 2012 at 10:38:10AM -0700, Jeff Janes wrote:
> On Wed, May 30, 2012 at 9:56 AM, Bruce Momjian <bruce(at)momjian(dot)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.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +