[HPADM] RE: Re: HP-UX Oracle/ Shared memory segment question

The case is Oracle try to keep SGA in one big block and you should consult your DBA about the recommended size of shared memory (and summarize SGA for all instances of Oracle). Each instance deal with own shared memory segment and this is not a problem. BTW set SGA of size of total memory is not wise.
According to the info you provide I see 6 instances of Oracle, not 2

<><><><><><><><><><><><><><><><><><><><><>
Regards: Romeo Ninov
http://www.ninov.info
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-----Original Message-----
From: hpux-admin-owner@xxxxxxxxxxxxx [mailto:hpux-admin-owner@xxxxxxxxxxxxx] On Behalf Of Dan.Askew@xxxxxxxxxxxxx
Sent: Tuesday, December 29, 2009 6:37 PM
To: simon.loewenthal@xxxxxxxxx
Cc: hpux-admin@xxxxxxxxxxxxx; hpux-admin-owner@xxxxxxxxxxxxx
Subject: [HPADM] Re: HP-UX Oracle/ Shared memory segment question

After reading this...

Does this mean if you set the shmax to be the same size of the memory on
the machine then you should only have 6 database instances running ???

Does anyone know the degradation factor ... are we talking 5% or 15% ...
this makes a big difference

Lastly - instead of making the shmax the same size of the server ... should
it be the same size as the largest SGA of a database?


Dan Askew
Sr Systems Administrator
The J. M. Smucker Company







From: Simon Loewenthal <simon.loewenthal@xxxxxxxxx>

To: hpux-admin@xxxxxxxxxxxxx

Date: 12/29/2009 07:27 AM

Subject: [HPADM] HP-UX Oracle/ Shared memory segment question

Sent by: hpux-admin-owner@xxxxxxxxxxxxx







Dear all,

I read the article below about setting the shared memory for Oracle. My
knowledge of Oracle is poorly. Does the article imply that each instance
of of the pmon process should only have six shared memory segments afore it
runs out of protection keys?

What happens if there are two instances of pmon running on the server each
with six shared mem segments (12 in total) - Is performance degraded?

Should ipcs -m only show a maximum of six shared mem., segments afore
performance is impacted? ; Each pmon process takes at least one shared
memory segment.

e.g

# ipcs -m | grep oracle
m 131080 0x1883dd84 --rw-r----- oracle dba
m 32777 0xf36e5128 --rw-r----- oracle dba
m 65546 0x58d5f298 --rw-r----- oracle dba
m 32779 0xeb079cb4 --rw-r----- oracle dba
m 65548 0xcc76dbcc --rw-r----- oracle dba
m 32781 0xaf9e2c2c --rw-r----- oracle dba
# ps -eaf|grep pmon
oracle 18861 1 0 11:54:44 ? 0:00 ora_pmon_1PRD
oracle 17349 1 0 11:51:12 ? 0:01 ora_pmon_2PRD
oracle 17170 1 0 11:50:59 ? 0:00 ora_pmon_3PRD
oracle 21703 1 0 12:11:45 ? 0:00 ora_pmon_4PRD
oracle 17325 1 0 11:51:09 ? 0:00 ora_pmon_5PRD
root 3310 3117 0 13:07:50 pts/1 0:00 grep pmon
oracle 16960 1 0 11:50:21 ? 0:00 ora_pmon_6PRD

Any clues would be gratefully appreciated.

Merry Xmas & a happy New Year!

Regards, S.

------------------------------------------------------------------------------------------------



http://download.oracle.com/docs/html/A97297_01/appb_hp.htm

HP-UX Shared Memory Segments for a 64-Bit Oracle Instance

When a 64-bit Oracle server creates a database instance, the server creates
memory segments by dividing the available shared memory by the value of the
HP-UX SHMMAX kernel parameter. For example, if 64 GB of shared memory is
available for a single Oracle instance and the value of the SHMMAX
parameter is 1 GB, the Oracle server creates 64 shared memory segments for
that instance.

In laboratory tests, performance degradation occurs when an Oracle instance
creates more than six shared memory segments. This is because each shared
memory segment receives a unique protection key when the Oracle server
creates the instance. There are six protection keys available for shared
memory segments on the PA-RISC processor. If your system has more than six
shared memory segments, the HP-UX operating system displays protection key
faults.Oracle Corporation recommends that you set the SHMMAX parameter
value to the amount of available physical memory on the system. Doing this
ensures that the entire shared memory for a single Oracle instance is
assigned to one shared memory segment and your instance needs only one
protection key. To display the list of active shared memory segments on the
system, enter the following command: $ ipcs -m


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