Can I increase the SHMMAX  (Shared Memory Max) value from 16GB to 64GB?

Posted on 2009-02-19
Medium Priority
Last Modified: 2013-12-27
I wants to increase the value of SHMMAX from 16GB to 64GB as Oracle expert recommended. The expert recommended to increase it from existing 16GB to 64GB. Is there any side effect to the system? Can Solaris 8 accept?  

The server has 160GB of memory. And SHMMAX=Max Shared Memory Segment. If I use the recommendation from Oracle expert which is 64GB, 2 segments will use 128GB of memory. Is it possible to grab 128GB of memory on the fly. Since the server has 160GB of memory, he can at most grab 2 segments, provided there is enough memory.

----- Current value ----
* IPC Shared Memory
8589934592 max shared memory segment size (SHMMAX)
512 shared memory identifiers (SHMMNI)
Thanks in advance,
Question by:Dujin

Accepted Solution

peter991 earned 1500 total points
ID: 23689507
That depends on wich version of Solaris is used.
Earlier versions could cause the OS to run out of memory/swap.
In your case Solaris 8, I belive it has safeties built into to prevent that.

In Solaris10, setting kernel parameters in /etc/system is an obsolete method. Solaris 10 has a Resource Manager which is used to adjust these kernel params.



Author Closing Comment

ID: 31549058
The website below is the correct document for me.
As the document said "Setting this value high does not hurt anything, as this merely is a limit - nothing is pre-allocated.", increasing the SHMMAX value should be OK.

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