Date: Thu, 4 Aug 2005 12:13:12 -0700 From: Sean Chittenden <sean@gigave.com> To: Bruce Walker <bmw@borderware.com> Cc: freebsd-performance@freebsd.org Subject: Re: changing max_connections in postgresql on FreeBSD 5.4 Message-ID: <20050804191312.GF70123@sean.gigave.com> In-Reply-To: <42F25526.5030002@borderware.com> References: <b41c755205080410013348d0f@mail.gmail.com> <20050804174508.GA70123@sean.gigave.com> <42F25526.5030002@borderware.com>
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> >>Will more RAM become available to postgresql if I change the > >>kernel-values mentioned above to half the size? > > > >Yes, it will raise the in-kernel limits so that PostgreSQL can > >allocate more RAM for its user-land cache. > > > >You will probably have a better ROI in terms of performance by > >increasing the kernel's caching parameters as opposed to > >PostgreSQL's cache. You need both, don't get me wrong, but there > >is lots of performance to be gained by increasing the amount of > >caching the kernel does. -sc > > Any generally good rules of thumb you could share? Which kernel > caching are you referring to (ie disk, ...) ? Hrm... I'll suggest one tunable: options KSTACK_MAX_PAGES=32 # Maximum pages to give the kernel stack Don't crank it up too far, but 64 seems to be a decent number in my experience. I'd pimp more settings, but given that tuning is still closer to an art than a science (it wouldn't be if someone catalogued settings for various applications and hardware combinations, but I digress), I'll suggest having you take a peak at the various NOTES files and some of the headers, such as: src/sys/amd64/include/param.h. I've divulged more in the archives, too. -sc -- Sean Chittenden
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