topic oracle instance processes in Operating System - HP-UX

oracle instance processes

Joe Profaizer — Thu, 19 Jul 2001 19:11:56 GMT

When we try to start up an oracle instance with processes set at 500 we get an error.

Changing the instance parameter to 400 allows it to start

ipcs -as shows NSEMS for an Oracle owned semaphore at 404, so we're assuming this is the value that we're exceeding when we set it to 500.

Just need to find out what kernel parameter is related to that.

Re: oracle instance processes

John Poff — Thu, 19 Jul 2001 19:55:21 GMT

Hello Joe,

When you say "processes" and "instance parameter", what exactly are you referring to? Is that the 'nproc' kernel parameter? The 'semmni' kernel parameter is the number of semaphore identifiers, and on the box I'm looking at it uses the formula (NPROC*2), so it would be tied into the number of processes.

If you are running Oracle you could have a ton of processes. You might need to bump up NPROC to a much higher number. On the box I'm looking at (big Oracle V-class box), we have it set at 2794.

JP

Re: oracle instance processes

Andreas D. Skjervold — Fri, 20 Jul 2001 06:17:06 GMT

Hi
The kernel parameter SEMMNS is related to the init.ora parameter processes and should be set to a value higher than the sum of processes for all your instances.

I usually set SEMMNS = processes x 2

Andreas

Re: oracle instance processes

Wodisch — Fri, 20 Jul 2001 16:15:45 GMT

Hello Joe,
did you not ask this question the day before somewhere
else on the forums???
Anyway, depending on you release of Oracle8, you might
need to have a lot more semaphores than you actually
use... There are some circumstances, when Oracle8
does not free the semaphores fast enough upon
shutdown, so they still used when the instances starts
again :-(
But semaphores are cheap (kind of), hence no problem
in allocating a couple of thousands of them in your
kernel. Remember that HP-UX, and CDE, and other
applications do use semaphores, too.

Conclusion: make the kernel parameter SEMMNS a
multiple of your init*ora parameter PROCESSES, and
do add even some more of them.

HTH,
Wodisch