In this post, I am sharing tips on VSAM files. These are useful for your project and interviews.
VSAM File Tips For Mainframe Programmers
- Entries in Master or User catalog is possible for VSAM datasets.
- In general, the Master catalog and User-catalog both can have entries of VSAM and non-VSAM datasets.
- Only KSDS datasets have Indexed. ESDS and RRDS do have only the data components. That means they do not have an index.
- |Data component|Index component|
- While working with ESDS and RRDS you no need to use index.
- KSDS has an index is a combination of Key and Value. KSDS also supports an alternate index.
- Index key|Sequence value
- In KSDS first, it locates the index, then finds corresponding sequence value later it get data from control interval and area.
- The catalog that stores both VSAM and non-VSAM datasets information is called the ICF integrated catalog facility.
How to Write Logic in COBOL program to access VSAM files
SELECT TEST1 ASSIGN TO TEST1 ORGANIZATION IS INDEXED ACCESS IS RANDOM RECORD-KEY IS TS-EMPLOYEE-NUMBER ALTERNATE RECORD KEY IS TS-SOCIAL-SECURITY-NO ALTERNATE RECORD KEY IS TS-DEPT-NO WITH DUPLICATES.