Re: configure shmmax on MAC OS X

On OS X, I've always made these changes in:

/System/Library/StartupItems/SystemTuning/SystemTuning

and manually checked it with sysctl after reboot.  Works for me.

100k buffers is probably overkill.  There can be a performance penalty with too many buffers.  See this lists' archives for more.  10k would probably be a better start.

- Jeff


>Hi, all,
>
>I have got a new MaC OS G5 with 8GB RAM. So i tried to increase
>the shmmax in Kernel so that I can take advantage of the RAM.
>
>I searched the web and read the manual for PG7.4 chapter 16.5.1.
>After that, I edited /etc/rc file:
>
>sysctl -w kern.sysv.shmmax=4294967296 // byte
>sysctl -w kern.sysv.shmmin=1
>sysctl -w kern.sysv.shmmni=32
>sysctl -w kern.sysv.shmseg=8
>sysctl -w kern.sysv.shmall=1048576 //4kpage
>
>for 4G shared RAM.
>
>Then I changed postgresql.conf:
>shared_buffer=100000 //could be bigger?
>
>and restart the machine and postgres server. To my surprise, postgres server wouldn't
>start, saying that the requested shared memory exceeds kernel's shmmax.
>
>My suspision is that the change i made in /etc/rc does not take effect.Is there a way
>to check it?  Is there an
>up limit for how much RAM can be allocated for shared buffer in MAC OS X? Or
>is there something wrong with my calculation in numbers?
>
>Thanks a lot!
>
>Qing
>
>
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-- 

Jeff Bohmer
VisionLink, Inc.
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www.visionlink.org
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