topic semaphores alarm in Operating System - HP-UX

semaphores alarm

Troyan Krastev — Wed, 08 Aug 2001 14:20:01 GMT

Hi all,

I have BMC Patrol installed on one of my HP-UX boxes and it raise an alarm that number of SemaphoreOperations are getting to low. I run ?sar ?m? and this is a part of the output:
silver:/ # sar -m 1 2000
HP-UX silver B.11.00 C 9000/889 08/08/01
11:06:00 msg/s sema/s
11:06:01 0.00 532.67
11:06:02 0.00 529.29
11:06:03 0.00 516.00
11:06:04 0.00 44.00
11:06:05 0.00 0.00
11:06:06 0.00 72.73
11:06:07 0.00 198.02
11:06:08 0.00 0.00
11:06:09 0.00 125.25
11:06:10 0.00 524.00
11:06:11 0.00 510.89

Is it really a problem? And if it is, where can I find some more information on it?

Thanks,
Troy.

Re: semaphores alarm

JACQUET — Wed, 08 Aug 2001 14:38:21 GMT

This is a part of some kernel parameter on HP-UX.
When you setup Patrol, do they give some tips about system resources ? As Share Memory, Semaphores, ...
First, check the following kernel parameters :
- semmap
- semmni
- semmns
- semvmx
Compare semmns with sar -m and see if semmns is too short. Then increase this parameter. You'll maybe have to increase also semmap, semmni.
Refer to the kernel parameter documentation for that.
In any case, that won't be a problem for your HP9000, simply kernel tables will be full, and software programms may coredump.

PJA.

Re: semaphores alarm

Praveen Bezawada — Wed, 08 Aug 2001 14:41:29 GMT

Hi
You can try in Glance...
the system table report gives information about the number of semaphores being used and the total available,
If the total available is less you can increase the kernel value of
semmns ( total no of semaphores )
semmni ( total semaphore indentifiers, that is maximum sempahores that can be used at any point
of time)

...BPK...

Re: semaphores alarm

Troyan Krastev — Wed, 08 Aug 2001 15:38:31 GMT

Hi Jaquet,

These are my parameters:
semmap 66
semmni 64
semmns 200
semvmx 32767
Is sema/s = 0 mean that all semaphores are in use???

Re: semaphores alarm

Troyan Krastev — Wed, 08 Aug 2001 15:41:02 GMT

Hi Praveen,

I will install Glance to see what I can find!

Re: semaphores alarm

Rita C Workman — Wed, 08 Aug 2001 16:11:35 GMT

To know what your semaphores need to be set at is based on what your process/apps is asking for. In the case of Oracle you would check the ~init.ora file and see what amount of processes it is set at .. then with this information you can 'begin' to calculate and setup your parm values for the semm* parms.
Here are two threads....the first is docs on parms -check out min/max of semms; and the second will give you how to calculate the semm* values.
1.)http://docs.hp.com//hpux/onlinedocs/os/KCparams.OverviewAll.html
2.)http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0x10ca6af52b04d5118fef0090279cd0f9,00.html

Now here's one last tip. It may not be applicable in your apps, you'll have to determine. Some folks forget that some apps also use alot of message queues msg* so if your apps use this then you need to address how you set these parms as well.

Just a thought,
Rita

Re: semaphores alarm

Troyan Krastev — Wed, 08 Aug 2001 16:56:35 GMT

Thanks all for the information. I will investigate the problem.

Troyan.

Re: semaphores alarm

JACQUET — Thu, 09 Aug 2001 12:37:18 GMT

sema/s tells how many semop() system call (semaphore operation) happen in one second.
So, if sema/s=0, that means that no semop() system call happen, not that semaphore table (semmns) is full.
I could suggest to put semmns=600
and semmni=300, and try with those values.
(semmap is semmni + 2 and would be automatically changed if you kept the default value for calculation)

PJA.