Re: FreeBSD 7 needing to allocate lots of shared memory

Christiaan Willemsen wrote:
> Bill Moran wrote:
>> In response to Christiaan Willemsen <cwillemsen@technocon.com>:
>>
>>
>>> #sysctl -a | grep shm
>>> kern.ipc.shm_allow_removed: 0
>>> kern.ipc.shm_use_phys: 1
>>> kern.ipc.shmall: 68719476736
>>> kern.ipc.shmseg: 128
>>> kern.ipc.shmmni: 192
>>> kern.ipc.shmmin: 1
>>> kern.ipc.shmmax: 68719476736
>>>
>>
>> Try bumping shmmni:
>> $ sysctl -d kern.ipc.shmmni
>> kern.ipc.shmmni: Number of shared memory identifiers
>>
>> I have this set to 1000 on most of my systems.  Can't seem to find my
>> notes on it right now, but that may be your holdup.  The PG docs seem
>> to indicate that this number can be set very low, as PG only needs a
>> single identifier, but I must have had _some_ reason for raising it.
>>
 > Hello Bill,
 >
 > I have this one set to 512 in loader.conf
 > other params in loader.conf:

Your sysctl output above shows kern.ipc.shmmni is set to 192

 > kern.ipc.semmni=1024
 > kern.ipc.semmns=1024
 > kern.ipc.semmnu=512

Take a close look here.

Christiaan mentioned kern.ipc.shmmni the list above shows
kern.ipc.semmni (you may only be listing others)

Double check that your settings are what you expect.

Also check /etc/sysctl.conf which may override some of the changeable
options from loader.conf.

Settings in loader.conf are only required for read-only options (that
need a reboot to take effect). Others are often changed in sysctl.conf

Check your running settings against what you expect.



Just a guess here - kern.ipc.shmall and kern.ipc.shmmax seem very high
but not sure if this can lead to the issue.

 > sysctl -d kern.ipc.shmmax
kern.ipc.shmmax: Maximum shared memory segment size

 > sysctl -d kern.ipc.shmall
kern.ipc.shmall: Maximum number of pages available for shared memory

Looks like you have set this to equal your installed RAM but a page is a
bit more than one byte. (is it 4K to a page?)



You haven't mentioned whether you are using the generic kernel or a
custom built one (with what changes?)


For reference - I have an old P4 3Ghz with 1GB RAM (32bit)
FreeBSD 7 release with a custom kernel to turn on the new scheduler

I can set shared_buffers to 64MB (you mentioned trouble over 32MB)

fbsd# sysctl -a | grep shm
kern.ipc.shm_allow_removed: 0
kern.ipc.shm_use_phys: 1
kern.ipc.shmall: 32768
kern.ipc.shmseg: 128
kern.ipc.shmmni: 192
kern.ipc.shmmin: 1
kern.ipc.shmmax: 134217728

fbsd# sysctl -a | grep sem
kern.ipc.semaem: 16384
kern.ipc.semvmx: 32767
kern.ipc.semusz: 92
kern.ipc.semume: 10
kern.ipc.semopm: 100
kern.ipc.semmsl: 60
kern.ipc.semmnu: 30
kern.ipc.semmns: 60
kern.ipc.semmni: 10
kern.ipc.semmap: 256

--

Shane Ambler
pgSQL (at) Sheeky (dot) Biz

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