Re: Buffers and MacOS X

>Tom Lane wrote:
>> Hunter Hillegas <lists@lastonepicked.com> writes:
>> > We are installing postgres on a MacOS X Server...
>> > On our Linux box, we had to muddle with some parameters to be able to
>> > increase the shared memory and buffers in postgres.
>> > Does anyone know how to do this in OS X? Or is it required?
>>
>> In OS X 10.1, the max shared memory was a hardwired number that couldn't
>> be changed without recompiling the kernel --- and the standard setting
>> was none too darn large, either :-(.  I dunno if Apple has improved
>> matters in 10.2.
>
>I was going to point him to the development docs, but I see no mention
>of OSX shared kernel limit tuning in there at all.  Can someone submit
>info to beef it up for OSX?


Here are instructions for setting shared memory limits on Mac OS X 10.2.

Edit the file:

    /System/Library/StartupItems/SystemTuning/SystemTuning

Near the bottom, you will see these lines:

    sysctl -w kern.sysv.shmmax=4194304
    sysctl -w kern.sysv.shmmin=1
    sysctl -w kern.sysv.shmmni=32
    sysctl -w kern.sysv.shmseg=8
    sysctl -w kern.sysv.shmall=1024

These parameters are described in this document:

    http://www.postgresql.org/idocs/index.php?kernel-resources.html

OS X is simialar to BSD/OS in the values for each parameter.  For my system, I want PostgreSQL to use 128MB worth of
buffers. I used the calculations provided in the "Reasonable Values" column of the parameters table in the document
above.

So here are my settings (allowing a little extra room):

    sysctl -w kern.sysv.shmmax=167772160    # bytes
    sysctl -w kern.sysv.shmmin=1
    sysctl -w kern.sysv.shmmni=32
    sysctl -w kern.sysv.shmseg=8
    sysctl -w kern.sysv.shmall=65536        # 4K pages

Now, I can set shared_buffers in postgresql.conf to:

    shared_buffers = 16384    # number of buffers, 8K each

- Jeff
--

Jeff Bohmer
VisionLink, Inc.
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