Mainframe, MVS and zOS Discussion

1. CICS, DB2, IMS can process records in existing VSAM data-sets but can't create the data-set. Even you can process VSAM data sets in COBOL programs only after you create them with access method services.

2. To specify dummy VSAM dataset in a JCL, Code AMP=’AMORG’ . This parameter tells the OS to treat the file as VSAM file. E.g.:

3. If you want to make VSAM-data-set read-only, use INHIBIT along with ALTER command:
Notice that the ALTER command is used with DATA and INDEX and not with the cluster.

4. A VSAM data-set created with REUSE can be treated as a new data-set at any subsequent time. In a way, you can say that VSAM equivalent of temp data-set is to create VSAM file with REUSE option.

5. IDCAMS Utility can't be executed without the SYSPRINT and SYSIN DD names.

Quite a good number of tips, Thanks for sharing them.

Regards,
Neeraj

Thanks for the feedback Neeraj - glad, you find them helpful.

Regards,

Thanks for the tip no. 3, I just used it.

Great - nice to know that!

Regards,

6. Advice: One should remove Catalog Orphans from the Catalog, (if you're in the capacity of doing it).

7. As an Application Developer (assuming COBOL as the Application language) - for sequential access of VSAM, request more data buffers. For random access, request more index buffers.

One should specify both BUFND and BUFNI when ACCESS IS DYNAMIC.

Avoid coding additional buffers unless your application will run interactively; then code buffers only when response-time problems arise that might be caused by delays in input and output.

8. As a COBOL Application Developer, if you can choose this -for 'best performance', access records sequentially.

Dynamic access is less efficient than sequential access, but more efficient than random access. Random access results in increased EXCPs because VSAM must access the index for each request.