Shared memory on AIX

If certain application types fail to connect because of an AIX memory limitation, in most cases this can be resolved by setting the environment variable EXTSHM=ON.

Some 32-bit processes on AIX might encounter an operating system limitation that affects their ability to connect to IBM MQ queue managers. Every standard connection to IBM MQ uses shared memory, but unlike other UNIX and Linux platforms, AIX allows 32-bit processes to attach only 11 shared memory sets.

Most 32-bit processes will not encounter this limit, but applications with high memory requirements might fail to connect to IBM MQ with reason code 2102: MQRC_RESOURCE_PROBLEM. The following application types might see this error:

• Programs running in 32-bit Java virtual machines
• Programs using the large or very large memory models
• Programs connecting to many queue managers or databases
• Programs that attach to shared memory sets on their own

AIX offers an extended shared memory feature for 32-bit processes that allows them to attach more shared memory. To run an application with this feature, export the environment variable EXTSHM=ON before starting your queue managers and your program. The EXTSHM=ON feature prevents this error in most cases, but it is incompatible with programs that use the SHM_SIZE option of the shmctl function.

IBM MQ MQI client applications and all 64-bit processes are unaffected by this limitation. They can connect to IBM MQ queue managers regardless of whether EXTSHM has been set.