Details of the migration
In this part, we describe the migration steps and considerations. These chapters address the numerous things that you need to consider if you are interested in replacing JES3 with JES2. An obvious difference is that the JES3 JECL is different from JES2 JECL. Therefore, you need to consider how you would identify and then replace all the JES3 JECL statements with alternatives that would provide the same net effect in a JES2 environment. Appendix A, “Sample JES3 exit to analyze JECL usage” on page 227 includes a JES3 exit routine that you can run to find these statements.
Other less obvious differences include things such as:
•Chargeback considerations because JES2 and JES3 have different ways of accounting for the CPU time used by applications for JES-related functions.
•Functions that are provided by JES3 that are not included in JES2. You will need to identify which ones you use, whether you would still need that function in a JES2 environment, and if so, how would you provide that function.
•User exits and user mods. Because the source code for both JES2 and JES3 is shipped with the product, it is not unusual to find that modifications have been made. You need to identify these changes and determine if they are still required and how you would provide that capability in a JES2 environment.
We begin with a summary, Chapter 6, “Planning for a JES3 to JES2 migration” on page 89. Then, we provide chapters on specific topics and components. To make it easier for you to make an objective assessment of the effort to migrate to JES2, some chapters conclude with a checklist of the items covered in that chapter. We suggest that you complete those checklists as you proceed through the book.
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