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Kernel Parameter setting explaination for Processes Parameter

Posted on 31-Aug-2006 By Admin No Comments on Kernel Parameter setting explaination for Processes Parameter

SHMMAX = The maximum size(in bytes) of a single shared memory segment.

SHMMIN = The minimum size(in bytes) of a single shared memory segment.

The above settings let the max be bigger then we wil ever use and the min much smaller. They are sufficient for pretty much all systems.

SHMMNI = The number of shared memory identifiers.

SHMSEG = The maximum number of shared memory segments that can be attached by a process.

The above settings should also be sufficient.

SEMMNS = The number of semaphores in the system.

Set to the sum of the PROCESSES parameter for each Oracle database the

largest one, plus 2 times the largest PROCESSES value, plus 10 number of Oracle

databases. For example, consider a system that has three Oracle instances with

the PROCESSES parameter in their initsid.ora files set to the following values:

ORACLE_SID=A, PROCESSES=100

ORACLE_SID=B, PROCESSES=100

ORACLE_SID=C, PROCESSES=200

The value of SEMMNS is calculated as follows:

SEMMNS = ((A=100) + (B=100)) + ((C=200) * 2) +

((# of instances=3) * 10) = 630

SEMMNI = The number of semaphore set identifiers in the system;

determines the number of semaphore sets that can be created at any one time.

SEMMSL = The maximum number of sempahores that can be in one

semaphore set. It should be same size as maximum number

of Oracle processes

(The PROCESSES parameter in the init.ora file).

Set to 10 plus the largest initsid.ora PROCESSES parameter of an Oracle

database on the system. The PROCESSES parameter can be found in each

initsid.ora file, loc ORACLE_HOME/dbs directory. The default value of PROCESSES

for the 8.1.5 prebuilt database is 50.

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