At this point the exit is passed information about the main program, a user word, and a control block to provide storage option values.

The storage tuning user exit is called whenever CICS® asks Language Environment for the size of the preallocated storage area to be used for Language Environment stacks and heaps. CICS makes this call whenever it is processing the first copy or a new copy of a load module

When running on CICS without automatic storage tuning, the storage tuning user exit can do the following:

1. It can enable or disable storage tuning for a module.
2. If the load module is enabled for the storage tuning, it can provide the storage values. This information is then used by Language Environment® to tell CICS to update its information about how much preallocated storage should be allocated for the program before CICS calls Language Environment to run the program.

The storage tuning values passed back from the storage tuning user exit for this call should match the values that the storage tuning user exit passes back in the enclave initialization call. If this is not done, preallocated storage allocations performed by CICS for Language Environment will not be the optimal size, and may result in additional GETMAINs.

When running on CICS with automatic storage tuning, the storage tuning user exit can do the following:

1. It can enable or disable Language Environment storage tuning for the load module.
2. If automatic storage tuning is wanted for the load module, the storage tuning user exit can provide the starting storage values used by Language Environment automatic storage tuning.