Re: changing max_connections in postgresql on FreeBSD 5.4

From: Sean Chittenden (sean_at_gigave.com)
Date: 08/04/05

  • Next message: gnn_at_freebsd.org: "Tarball of ported libmicro 0.3 available for testing..." 
    Date: Thu, 4 Aug 2005 12:13:12 -0700
To: Bruce Walker <bmw@borderware.com>

    > >>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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