Kernel configuration

 

WebSphere MQ makes use of System V IPC resources, in particular shared memory and semaphores. The default configuration of these resources, supplied with your installation, is probably adequate for WebSphere MQ but if you have a large number of queues or connected applications, you might need to increase this configuration.

We can determine the amount of System V IPC resources available by looking at the contents of the following files:

  /proc/sys/kernel/shmmax - The maximum size of a shared memory segment.
  /proc/sys/kernel/shmmni - The maximum number of shared memory segments.
  /proc/sys/kernel/shmall - The maximum amount of shared memory
                              that can be allocated.
  /proc/sys/kernel/sem    - The maximum number and size of semaphore sets
                              that can be allocated.

For example, to view the maximum size of a shared memory segment that can be created enter:

  cat /proc/sys/kernel/shmmax

To change the maximum size of a shared memory segment to 256 MB enter:

  echo 268435456 > /proc/sys/kernel/shmmax

To view the maximum number of semaphores and semaphore sets which can be created enter:

cat /proc/sys/kernel/sem

This returns 4 numbers indicating:

 SEMMSL - The maximum number of semaphores in a sempahore set
 SEMMNS - The maximum number of sempahores in the system
 SEMOPM - The maximum number of operations in a single semop call
 SEMMNI - The maximum number of sempahore sets  

For WebSphere MQ:

• the SEMMSL value must be 128 or greater

• the SEMOPM value must be 5 or greater

• the SEMMNS value must be 16384 or greater

• the SEMMNI value must be 1024 or greater

To increase the maximum number of semaphores available to WebSphere MQ, you should update the SEMMNS and SEMMNI values.

To configure these values every time the machine is restarted you are recommended to add these commands to a startup script in /etc/rc.d/...

• Maximum open files
  

• Maximum processes
  

 

Parent topic:

Installing a WebSphere MQ server

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