Date: Mon, 23 May 2005 11:47:55 -0400 From: Vivek Khera <vivek@khera.org> To: freebsd-stable@freebsd.org, freebsd-amd64@freebsd.org Subject: Re: Manipulating disk cache (buf) settings Message-ID: <BBF18F8A-15D6-4E44-9032-102E0393F40E@khera.org> In-Reply-To: <1116860293.10083.43.camel@lanshark.dmv.com> References: <1116860293.10083.43.camel@lanshark.dmv.com>
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On May 23, 2005, at 10:58 AM, Sven Willenberger wrote: > We are running a PostgreSQL server (8.0.3) on a dual opteron system > with > 8G of RAM. If I interpret top and vfs.hibufspace correctly (which show > values of 215MB and 225771520 (which equals 215MB) respectively. My > understanding from having searched the archives is that this is the > value that is used by the system/kernel in determining how much disk > data to cache. > This is correct, from what I understand. If you take the vfs.hibufspace and divide by the page size for postgres (normally 8192) you get the proper value for the postgres tunable effective_cache_size. However, the value you see is also the max FreeBSD will use without hacking up the kernel sources. I asked about this a while back and got a response on what to hack, but I hate keeping local patches to the core system which often tend to be forgotten on upgrades... But I would also love to see the max cache get bigger, especially with multi-gig servers becoming more common and affordable. This will kill us on benchmark comparisons for large databases for sure. Vivek Khera, Ph.D. +1-301-869-4449 x806
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