Date: Thu, 30 Dec 2010 18:15:34 -0600 From: Jim Nasby <jim@nasby.net> To: Nicolas Haller <nicolas.haller@corp.nerim.fr> Cc: freebsd-performance@freebsd.org Subject: Re: tunning disk cache for pgsql? Message-ID: <AABD98FE-DA25-4A09-86D6-EBC341040A35@nasby.net> In-Reply-To: <20101228135940.GE2660@baneblade.noc.nerim.net> References: <20101228135940.GE2660@baneblade.noc.nerim.net>
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On Dec 28, 2010, at 7:59 AM, Nicolas Haller wrote: > I use a new box with 4GB RAM as a pgsql server. In pgsql, you can > set the effective_cache_size to indicate the memory available to cache > disk I/O. > As "recommended", my box use 1300MB to shared buffers (IPC shared = memory) > and 2700 Mo to disk cache. That's probably not a great mix unless your workload is very read-heavy. = Writes will push data through shared buffers back into the OS, which = will also try to cache it, so you'll end up with double-buffering. > If I look memory usage in top, it say: > Mem: 1154M Active, 1911M Inact, 601M Wired, 112M Cache, 417M Buf, 148M = Free The Cache reported by top in FreeBSD isn't filesystem cache; it's a = cache for some internal stuff. Buf are filesystem buffers, but they're = not the only mechanism for the OS to cache data. Most data is actually = cached via active and inactive pages. -- Jim C. Nasby, Database Architect jim@nasby.net 512.569.9461 (cell) http://jim.nasby.net
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