Tuning for PostGreSQL Database

Terry Lambert tlambert2 at mindspring.com
Tue Jul 22 23:23:07 PDT 2003

Christopher Weimann wrote:
> On Sun 07/20/2003-01:53:39PM -0700, Sean Chittenden wrote:
> > You might want to get in the habit of using sysctl for getting that
> > kind of info.  `sysctl -d vfs.bufspace`
> I'm confused.  Everything I have ever read about FreeBSD indicates
> that it uses all free ram for the disk cache.

FreeBSD uses all unwired free memory for caching.  Wired free
memory has, by definition, been committed to a type-stable zone,
and is therefore unavailable for reallocation, since it may have
been (probably *has* been) fragmented into sub-page-size fragments
that cannot be recoelesced into pages, even if they are all free,
so that they can be given back to the system.

There are some types of kernel allocations that are recoverable
(e.g. buffer cache entries/VM), but most allocations use the zone
allocator, and once it owns a page's soul, that page belongs to
it forever.

You should read Matt Dillon's excellent VM articles in the Blue
Prints column at http://www.daemonnews.org/ for more information.

-- Terry

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