General
cancel
Showing results for 
Search instead for 
Did you mean: 

Why do I have 5 shared memory segments

Emil Velez
Honored Contributor

Why do I have 5 shared memory segments

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
9 REPLIES
Viktor Balogh
Honored Contributor

Re: Why do I have 5 shared memory segments

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
****
Unix operates with beer.
Emil Velez
Honored Contributor

Re: Why do I have 5 shared memory segments

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
Emil Velez
Honored Contributor

Re: Why do I have 5 shared memory segments

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

Horia Chirculescu
Honored Contributor

Re: Why do I have 5 shared memory segments

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.
Best regards from Romania,
Horia.
Emil Velez
Honored Contributor

Re: Why do I have 5 shared memory segments

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.

Horia Chirculescu
Honored Contributor

Re: Why do I have 5 shared memory segments

This is strange...

How big is SEGSZ reported by ipcs?

Horia.

Best regards from Romania,
Horia.
Emil Velez
Honored Contributor

Re: Why do I have 5 shared memory segments

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

Re: Why do I have 5 shared memory segments

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

Can you post your kernel configuration parameters here?

Horia.
Best regards from Romania,
Horia.
Emil Velez
Honored Contributor

Re: Why do I have 5 shared memory segments

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