AIX Version 4.3.1 introduced the EXTSHM environment variable to support use of the extended shared memory model. To use this memory model, export the variable "EXTSHM=ON" in the environment of the process.
WebSphere MQ makes use of the extended shared memory model. All WebSphere MQ processes automatically set EXTSHM in their environment and you should set this environment variable in the environment of all WebSphere MQ applications.
The EXTSHM environment variable must be set in the environment before the application starts. Using "putenv()" once the application has started will have no effect. For more information about the use of extended shared memory see the AIX documentation.
By default, a program running under AIX may only attach 10 shared memory segments in the process address space. Setting the environment variable "EXTSHM=ON" allows many more segments to be attached.
A standard WebSphere MQ application tries to attach 5 shared memory segments, so even without EXTSHM set ON the application will be able to attach to a queue-manager and function normally. However if the WebSphere MQ system is very busy, or if the application has many concurrent connections to the WebSphere MQ queue manager then it may need to attach more than the standard 5 shared memory segments.
Other parts of an application, for example database connections, may also use shared memory segments. If the total number of required segments exceeds 10, and EXTSHM is not set ON, then requests to the WebSphere MQ queue manager may fail.