File Handling & Temporary Storage

1. File Handling & Temporary Storage Day4

2. Objectives • Access Methods • VSAM • BDAM • VSAM Considerations • Random access • Sequential access • Temporary Storage Control • Commands to read, write and delete • Design considerations • Examples • Transient Data Control • Intrapartition TD queues • Extrapartition TD queues • Commands to read, write and delete • Examples

3. CICS File Control • VSAM • Allows read, browse, update and delete operations • BDAM • Allows read, browse and update only • They are less efficient than VSAM • Can be replaced by a relative record VSAM dataset or ESDS addressed by RBA

4. Types of VSAM Files • ESDS - Entry Sequenced Data Set • KSDS - Key Sequential Data Set • RRDS - Relative Record Data Set

5. Alternate Indexes in VSAM • Accessing same set of records in different ways • Any number of alternate keys • Alternate keys need not be unique • Only KSDS and ESDS can have alternate keys

6. Random access - READ MOVE +80 TO WS-EMP-REC-LEN. MOVE ‘10000’ TO WS-EMP-REC-KEY. MOVE 5 TO WS-EMP-KEY-LEN. EXEC CICS READ FILE (‘EMPFILE1’) INTO (WS-EMP-REC) LENGTH (WS-EMP-REC-LEN) RIDFLD (WS-EMP-REC-KEY) KEYLENGTH (WS-EMP-KEY-LEN) END-EXEC. • Places the record in WS-EMP-REC

7. GENERIC READ MOVE +80 TO WS-EMP-REC-LEN. MOVE ‘10’ TO WS-EMP-REC-KEY. MOVE 2 TO WS-EMP-KEY-LEN. EXEC CICS READ FILE (‘EMPFILE1’) INTO (WS-EMP-REC) LENGTH (WS-EMP-REC-LEN) RIDFLD (WS-EMP-REC-KEY) KEYLENGTH (WS-EMP-KEY-LEN) GENERIC END-EXEC.

8. READ Continues... • READ COMMAND OPTIONS • EQUAL • GTEQ • UPDATE • READ-UPDATE/REWRITE • Maintains exclusive control on the resource(on CI in case of VSAM file) until • REWRITE is done • Transaction ends normally or abnormally • Control over resource is released by program using UNLOCK command.

9. REWRITE • To rewrite records into file. EXEC CICS REWRITE FILE (‘EMPFILE’) FROM (WS-EMP-REC) LENGTH (WS-EMP-REC-LEN) END-EXEC. • This command updates a record. • Prior to this command the record must be read with a READ UPDATE command.

10. WRITE • To write records into file. MOVE +80 TO WS-EMP-REC-LEN. MOVE ‘11000’ TO WS-EMP-REC-KEY. MOVE 5 TO WS-EMP-KEY-LEN. EXEC CICS WRITE FILE (‘EMPFILE’) FROM (WS-EMP-REC) LENGTH (WS-EMP-REC-LEN) RIDFLD (WS-EMP-REC-KEY) KEYLENGTH (WS-EMP-KEY-LEN) END-EXEC.

11. DELETE • Read the record with UPDATE option and then delete it with the following command. EXEC CICS DELETE FILE(‘EMPFILE’) END-EXEC. • Use the following command to delete the record directly. MOVE ‘12345’ TO EMP-REC-KEY. EXEC CICS DELETE FILE(‘EMPFILE’) RIDFLD (EMP-REC-KEY) END-EXEC.

12. GROUP DELETE • MOVE ‘11’ TO WS-EMP-REC-KEY. • MOVE 2 TO WS-EMP-KEY-LEN. EXEC CICS DELETE FILE (‘EMPFILE’) RIDFLD (WS-EMP-REC-KEY) KEYLENGTH (WS-EMP-KEY-LEN) GENERIC NUMREC (WS-NUM-REC-DEL) END-EXEC.

13. Transaction deadlocks • Exclusive control on CI. • Exclusive control may cause transaction deadlocks. Make sure to use UNLOCK when you are not rewriting • In pseudo-conversation, at the end of transaction, all locks are released.

14. Sequential access - Browsing • STARTBR • READNEXT • READPREV • RESETBR • ENDBR

15. STARTBR • This establishes a browse session. EXEC CICS STARTBR FILE (‘EMPFILE’) RIDFLD (EMP-REC-KEY) KEYLENGTH(KEY-LEN) GTEQ/EQUAL/GENERIC END-EXEC.

16. READNEXT/READPREV EXEC CICS READNEXT/READPREV FILE (‘EMPFILE’) INTO (EMP-REC) LENGTH (EMP-REC-LEN) RIDFLD (EMP-REC-KEY) END-EXEC.

17. RESETBR • Establish a new browsing position with in the same browse. MOVE ‘12345’ TO EMP-REC-KEY. EXEC CICS RESETBR FILE (‘EMPFILE’) RIDFLD (EMP-REC-KEY) GTEQ END-EXEC.

18. ENDBR • End browse operation EXEC CICS ENDBR FILE (‘EMPFILE’) END-EXEC.

19. Sequential access – VSAM ESDS Move Low-values to VSAM-ESDS-RBA EXEC CICS STARTBR DATASET (‘filename’) RIDFLD(ESDS-RBA) RBA EQUAL END-EXEC • EXEC CICS READNEXT • DATASET (‘filename’) • INTO(FILE-AREA) • RIDFLD(ESDS-RBA) • LENGTH(WS-LEN) • RBA • END-EXEC

20. Temporary Storage • COMMAREA (Communication Area) • CWA (Common Work Area) • TWA (Transaction Work Area) • TSQ (Temporary Storage Queue) • TDQ (Transient Data Queue)

21. TSQ Commands • WRITEQ TS EXEC CICS WRITEQ TS QUEUE (qname) FROM (recarea) LENGTH (length) option (option)… END-EXEC.

22. TSQ Commands • READQ TS EXEC CICS READQ TS QUEUE (qname) INTO (recarea) LENGTH (length) option END-EXEC

23. TSQ Commands • DELETEQ TS EXEC CICS DELETEQ TS QUEUE (qname) END-EXEC.

24. Transient Data Queue • 2 types of TDQ • Intra-partition • Extra-partition • Difference between TDQ and TSQ • TDQ to be defined in DCT • No modify or Rewrite option in TDQ • TDQ can be read only sequentially • A destructive read is performed on TDQ • A trigger can be set on Intrapartition TDQ • No counterpart to the MAIN option available in TSQ

25. TDQ Commands EXEC CICS WRITEQ TD QUEUE (qname) FROM (recarea) LENGTH (length) END-EXEC EXEC CICS READQ TD QUEUE (qname) INTO (recarea) LENGTH (length) END-EXEC • DFHDCT entry • TYPE=INTRA • DESTID=qname • TRANSID=EMPL • TRIGLEV=2000 EXEC CICS DELETEQ TD QUEUE (qname) END-EXEC

26. Summary • What is VSAM? • What are the types of VSAM files? • When do transaction deadlocks happen and how to avoid? • What are the commands for sequential access? • How is sequential access of ESDS done? • What is the difference between TSQ and TDQ? • What are the commands used to access TSQ and TDQ?

27. Thank You!