Intimate Shared Memory (ISM)

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Operating Systems Solaris Intimate Shared Memory (ISM)
# 1  
Old 10-20-2009
Question Intimate Shared Memory (ISM)

Dear all,

Anyone could help to explain me about ISM? I use SunOS 5.10 and have 3 questions here:

1. Is it true that the ISM value will be set to TRUE by default on either global or container box of Solaris?

2. Is it true if the ISM is TRUE, then the swap to disk (virtual memory) won't work (vmstat command will result 0 value in column po

3. What are the effects if I disable the ISM (set it to FALSE).


Last edited by sprout009; 10-20-2009 at 07:22 AM..
# 2  
Old 10-20-2009
What boolean "ISM value" are you referring to ?
# 3  
Old 10-20-2009

I refer to parameter USE_ISM. I ever read that this value is by default is being set to TRUE if it is not mentioned in /etc/system. Thanks.
# 4  
Old 10-20-2009
There is no such parameter in Solaris so setting USE_ISM in /etc/system would have no effect.
You might be confusing this with an oracle parameter (init.ora).
# 5  
Old 10-20-2009
Oops, my mistake.

I mean parameter _SHM_USE_ISM in /etc/system for Solaris, and parameter USE_ISM on initSID.ora for Oracle.

You're right, I have Oracle 10g on Solaris machine. I didn't find those parameters on both file system so I assume the ISM feature is ON.

What I know is that ISM doesn't support paging to disk. And I read that Oracle 9i supports DISM which supports paging to disk. So I'm wondering how to ensure whether my Oracle uses DISM feature or not. Do you know how to check this?

If my Oracle not in dynamic mode, since I have a limited resource of physical RAM, I'm afraid that this will cause system hang when simultaneous update executed. Your advice will be helpful. Thanks.
# 6  
Old 10-20-2009
If I recall correctly from my VOS days, ISM and DISM usage by Oracle is controled by the value of the SGA_MAX_SIZE tunable in init.ora. If it is unset, then you will use ISM. If set, then you will use DISM.

ISM, if I remember right, will cause pages of the Oracle SGA to be locked in memory. Other pages are still pagable.

If you set SGA_MAX_SIZE larger than your inital SGA then DISM is enable and ISM is disable. DISM can cause some unexpected performance issues...
# 7  
Old 10-20-2009
Could you help explain a bit why DISM can cause performance issue?

I tot with DISM, it is possible to swapped out the pages to disk so when I running out the physical RAM, I still can use the VM from harddisk?

Your guide will be helpful.

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