semaphore increase

[Todd McDaniel_1]

Hi,

I have never messed with changing semaphore values on my systems. So I need to know best/recommended way to increase them.

Here are my current settings on an N4000-55.


I believe the kernel parm to change is semmns, currently 4000, but I am not for sure. My DBA is asking me to increase it by double to 8000.

just double checking with you experts. My memory is 32GB... so it should be no problem.

# kmtune |grep sem
sema 1 - 1
semaem 16384 - 16384
semmap 1026 - (SEMMNI+2)
semmni 1024 - 1024
semmns 4000 - 4000
semmnu 1024 - 1024
semmsl 2048 Y 2048
semmsl_override - - 2048
semume 64 - 64
semvmx 32767 - 32767

[Pete Randall]

Todd,

For comparison, here's the values on my N4000-44 running 11.0/Informix:

kmtune |grep -i sem
sema 1
semaem 16384
semmap (SEMMNI+2)
semmni 4096
semmns 4096
semmnu 1024
semmsl_override 2048
semume 1024
semvmx 32767


Pete

[Graham Cameron_1]

We run 37 oracle instances on this box:
--
/usr/sbin/kmtune |grep -i sem
sema 1 - 1
semaem 16384 - 16384
semmap 16002 - (SEMMNI+2)
semmni 16000 - 16000
semmns 32000 - (SEMMNI*2)
semmnu 2996 - (NPROC-4)
semmsl 2048 Y 2048
semume 64 - 64
semvmx 32768 - 32768
--
The easiest way is via SAM, but there are more wizardly ways.
Whatever, it will need a reboot.
-- Graham

[Ravi_8 · Accepted solution]

Hi,

you can increase to 8000 it wouldn't cause any problem.

for one of our websphere appliaction we have following semaphores values set:

kmtune|grep -i sem
sema 1 - 1
semaem 16384 - 16384
semmap 1026 - (SEMMNI+2)
semmni 1024 - 1024
semmns 16384 - 16384
semmnu 2048 - 2048
semmsl 2048 Y 2048
semume 256 - 256
semvmx 32767 - 32767

[Steven E. Protter]

You might just want to ask him what his specific reasons are. Based on my own server settings and prior posts, its not going to cause problems.

You might want to collect some performance data.

I'd be hesitant about making a change without error messages or something from oracle metalink saying you should.

I'm attaching a data collection script that might point out you hitting limits.

SEP

[Todd McDaniel_1]

maybe Im not being clear... I need to increase my max semaphores...

Your comparisons are great but don't answer my question. I need your advice based on my DBAs request for doubling my # of semaphores.

1) Is semmns the correct parameter for that?

2) Are there any dependent parms that also need to be modified?

[Todd McDaniel_1]

Hehe, the first part of the last post was for the first few replies...

Thanks for your responses.

[Todd McDaniel_1]

I dont see doubling it as questionable, because I have semmns set to 10020 on my Production Superdome. Just wanted to make sure that with 32GB of memory it wouldnt be an issue, which I dont think that it is.

[Jeff Schussele]

Hi Todd,

To answer your question - Yes, semmns is the number of Sys V IPC system-wide semaphores.

Rgds,
Jeff

[Pete Randall]

Todd,

semmni is the system-wide max
semmns is the user accessible system-wide max
semmnu is the max undo per semaphore
semume is the max undos per process
semvme is the max allowed semaphore value

You can check SAM's "help on configurable paramters" for further details.


Pete