Date: Tue, 22 Jul 2003 23:21:50 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Christopher Weimann <cweimann@k12hq.com> Cc: Paul Pathiakis <paul@pathiakis.com> Subject: Re: Tuning for PostGreSQL Database Message-ID: <3F1E297E.70962D97@mindspring.com> References: <200307191818.13516.paul@pathiakis.com> <20030720110939.GN24507@perrin.int.nxad.com> <20030720164237.GC55392@nasby.net> <20030722143449.B10666@smtp.k12us.com>
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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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