topic Re: Why do I have 5 shared memory segments in Operating System - HP-UX

Why do I have 5 shared memory segments

Emil Velez — Wed, 07 Apr 2010 20:46:30 GMT

I have a oracle system with 11.1.6 on it

I installed oracle using all of the default installation parameters.
I created a database using dbca and unselected use enterprise manager and set the SGA to 1 GB.

Unlike oracle 10G I now have 5 shared memory segments instead of 1. My shmmax is set to 2 GB so my SGA is only using 1 shared memory segment. Any idea what the other segments are used for .

Points will be generous. Replies appreciated

Re: Why do I have 5 shared memory segments

Viktor Balogh — Thu, 08 Apr 2010 06:22:34 GMT

I think the shared memory was divided because of performance concerns. To disable this:

_enable_NUMA_optimization=FALSE

in the Oracle parameter file...

See metalink note nr. 399261.1

Re: Why do I have 5 shared memory segments

Emil Velez — Thu, 08 Apr 2010 06:27:10 GMT

ITs not the SGA shared memory segment. THey are relatively small and the system is not a cell based system.

I had a customer say that I should not have multiple shared memory segments even at 11.1

Re: Why do I have 5 shared memory segments

Emil Velez — Thu, 08 Apr 2010 18:38:02 GMT

I tried the numa parameter and I still had 5 shared memory segments.

Re: Why do I have 5 shared memory segments

Horia Chirculescu — Mon, 12 Apr 2010 08:01:48 GMT

Hello,

ipcs -mac

should give you the owner and the creator of the process using that shared memory segment.

Maybe not all shared memory segments from your system are created by Oracle.

Horia.

Re: Why do I have 5 shared memory segments

Emil Velez — Mon, 12 Apr 2010 10:45:34 GMT

I know about the IPCS command. The 5 shared memory segments are all owned by oracle and 27 processes are attached to them so I know that the 5 segments were created by this oracle instance.

Re: Why do I have 5 shared memory segments

Horia Chirculescu — Mon, 12 Apr 2010 11:11:47 GMT

This is strange...

How big is SEGSZ reported by ipcs?

Horia.

Re: Why do I have 5 shared memory segments

Emil Velez — Mon, 12 Apr 2010 11:20:13 GMT

I get the big one (the correct SGA size) and then 4 others between 2 and 8 mb

Re: Why do I have 5 shared memory segments

Horia Chirculescu — Mon, 12 Apr 2010 11:50:12 GMT

Do you have at least 4G of physical memory installed ?

Can you post your kernel configuration parameters here?

Horia.

Re: Why do I have 5 shared memory segments

Emil Velez — Mon, 12 Apr 2010 11:52:03 GMT

Yes system had 4 gb of memory

I lost system so I need to rebuild the oracle instance.

Kernel paramater shmmax was 2 GB which was larger than the 1.2 GB of SGA that was configured when I installed oracle.

all kernel parameters were set by tune-n-tools which set them correct for oracle