topic Re: Kernel Tuning w.r.t semaphores & shared memory in Operating System - Linux

Kernel Tuning w.r.t semaphores & shared memory

SSP_1 — Fri, 27 Jun 2003 04:29:17 GMT

Hi Guys,

System : - N-Class, hpux 11.00

We have approx. 15 db instances running on a N-Class server , all are with different versions eg. 8.1.7-32bit, 8.1.6-64bit, 9.2.0.2-32 , 9.2.0.2-64 , Yesterday we had have a serious problem where we have to brought down one database . After "shutdown abort" db was not going down and kill -9 was also not working for any of the oracle processes. I tried killing the semaphores & memory regions related to the particular instance with ipcrm but no luck. Atlast we have to reboot the server.

Now the question is why might this problem have aroused? Can we do any kernel tuning to take care it , to avoid this in future. Some of teh parameters which are of interest are
root@tbau01:>kmtune | grep -i shm
shmmax 2 GB
shmmni 512
shmseg 32

Can I tune this and to which extent , if yes. I am thinking to double the values of shmmax, shmmni, shmseg, Pl advise.

Thanx

Re: Kernel Tuning w.r.t semaphores & shared memory

Mike Brown_3 — Mon, 30 Jun 2003 12:02:57 GMT

To be honest, it looks like your configuration is like a lot of those with Oracle - quite complex!!
With such specifics, I would ask Oracle for their views on what your parameters should be.
I have some servers here that have been tuned similarly but it too is a very specific environment which may not truely represent yours.

Good luck, (sorry, perhaps not the informative response you might have hoped for).

Re: Kernel Tuning w.r.t semaphores & shared memory

Steven E. Protter — Mon, 30 Jun 2003 13:43:01 GMT

Few things to consider

shmmax will ignore settings greater than 25% of totoal memory.

Total memory is defined as physical memory plus swap.

Swap in general for systems with less than 16 GB of ram should be between 1.5 and 2 times physical memory.

shmseg might be a little low, but you need to collect some performance data to see if that is the issue.

To that end, I'm attaching a script. I also have some information from one of HP's prime oracle tuners and may want to collect additional data.

Script is attached....

With so many versions of Oracle running on the server, you may have a combination that Oracle never tested.

As a long term goal, I would suggest trying to migrate to all instances running in one central version in the 8 series, say 8.1.7.4.0 and one common version in the 9 series.

This could be an oracle problem.

itrc is giving me trouble accessing mhy Oracle Tuning documentation. I'll get back to you with it when itrc lets me get back to you with it.

SEP