Increase the stack size on Windows, Linux, and UNIX systems by setting the MQSI_THREAD_STACK_SIZE environment variable to an appropriate value. When you restart brokers that are running on the system, they use the new value.
The value of MQSI_THREAD_STACK_SIZE that you set is used for every thread that is created within a DataFlowEngine process. If the execution group has a large number of message flows assigned to it, and you set a large value for MQSI_THREAD_STACK_SIZE, the DataFlowEngine process therefore needs a large amount of storage for the stack.