Re: shared_buffers > 284263 on OS X

Brian,
On 16-Nov-06, at 7:03 PM, Brian Wipf wrote:

> I'm trying to optimize a PostgreSQL 8.1.5 database running on an
> Apple G5 Xserve (dual G5 2.3 GHz w/ 8GB of RAM), running Mac OS X
> 10.4.8 Server.
>
> The queries on the database are mostly reads, and I know a larger
> shared memory allocation will help performance (also by comparing
> it to the performance of the same database running on a SUSE Linux
> box, which has a higher shared_buffers setting).
>
> When I set shared_buffers above 284263 (~ 2.17 GB) in the
> postgresql.conf file, I get the standard error message when trying
> to start the db:
>
> FATAL:  could not create shared memory segment: Cannot allocate memory
> DETAIL:  Failed system call was shmget(key=5432001,
> size=3289776128, 03600).
>
> shmmax and shmall are set to 4GB, as can be seen by the output from
> sysctl:
> hw.physmem = 2147483648
> hw.usermem = 1885794304
> hw.memsize = 8589934592
> kern.sysv.shmmax: 4294967296
> kern.sysv.shmmin: 1
> kern.sysv.shmmni: 32
> kern.sysv.shmseg: 8
> kern.sysv.shmall: 1048576
>
> Has anyone else noticed this limitation on OS X? Any ideas on how I
> might get shared_buffers higher than 284263?

My guess is something else has taken shared memory ahead of you. OS X
seems to be somewhat strange in how it deals with shared memory. Try
allocating more to shmmax ?

Dave
>
> Brian Wipf
> <brian@clickspace.com>
>
>
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