A couple of months ago I’ve written a post on how to dynamically update the Linklist but some questions have been risen on why we need to stop the LLA and unallocate the Linklist.
Each Linklist dataset has an ENQ from both XCFAS and LLA. An ENQ on a LNKLST dataset prevents that dataset from being altered as long as it is a member of an active LNKLST. So, in order to be able to make changes to the active Linklist you first need to remove those ENQs.
To be able to remove the LLA ENQs you need to stop the LLA. The only impact that stopping the LLA has in the system is loss of performance until you re-start the LLA.
As per the XCFAS ENQs to remove them you need to issue the SETPROG LNKLST UNALLOCATE command. Unallocate indicates that you want to undo all existing allocations obtained while processing active LNKLST sets.
Once you remove the ENQs you are then able to change the Linklist. Now, bear in mind that although you have removed the ENQs the modules are still in Linklist. No abend will come out of this.
Once you are finished with the Linklist changes, you then restart the LLA and ALLOCATE the Linklist.
The UPDATE command indicates that the system is to update an address space so that a specified job or jobs associated with that space can use the current LNKLST set. If the job is using another LNKLST set when the current LNKLST set is activated, it will continue to use the original LNKLST set until it completes operations. When the job completes and restarts, it then uses the datasets defined in the new currently active LNKLST set.