File Handling & Temporary Storage Day4 2 Copyright © 2005, Infosys Technologies Ltd ER/CORP/CRS/TP01/003 Version No: 1.0 Objectives Access Methods –VSAM

File Handling & Temporary StorageDay4

2Copyright © 2005, Infosys Technologies Ltd

ER/CORP/CRS/TP01/003 Version No: 1.0

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



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



Types of VSAM Files

• ESDS - Entry Sequenced Data Set

• KSDS - Key Sequential Data Set

• RRDS - Relative Record Data Set



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



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



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.



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.



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.



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.



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.



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.



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.



Sequential access - Browsing• STARTBR

• READNEXT

• READPREV

• RESETBR

• ENDBR



STARTBR

• This establishes a browse session.

EXEC CICS STARTBR



KEYLENGTH(KEY-LEN)

GTEQ/EQUAL/GENERIC

END-EXEC.



READNEXT/READPREV

EXEC CICS READNEXT/READPREV


INTO (EMP-REC)

LENGTH (EMP-REC-LEN)


END-EXEC.



RESETBR

• Establish a new browsing position with in the same browse.

MOVE ‘12345’ TO EMP-REC-KEY.

EXEC CICS RESETBR



GTEQ

END-EXEC.



ENDBR

• End browse operation

EXEC CICS ENDBR


END-EXEC.



Sequential access – VSAM ESDSMove 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



Temporary Storage

• COMMAREA (Communication Area)

• CWA (Common Work Area)

• TWA (Transaction Work Area)

• TSQ (Temporary Storage Queue)

• TDQ (Transient Data Queue)



TSQ Commands

• WRITEQ TS

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



TSQ Commands

• READQ TS

EXEC CICS READQ TS

QUEUE (qname)

INTO (recarea)

LENGTH (length)

option

END-EXEC



TSQ Commands

• DELETEQ TS

EXEC CICS DELETEQ TS

QUEUE (qname)

END-EXEC.



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



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

EXEC CICS DELETEQ TD

QUEUE (qname)

END-EXEC

DFHDCT entry

TYPE=INTRA

DESTID=qname

TRANSID=EMPL

TRIGLEV=2000



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?



Thank You!

Documents

File Handling & Temporary Storage Day4 2 Copyright © 2005, Infosys Technologies Ltd ER/CORP/CRS/TP01/003 Version No: 1.0 Objectives Access Methods –VSAM