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 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.