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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
3Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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
4Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
Types of VSAM Files
• ESDS - Entry Sequenced Data Set
• KSDS - Key Sequential Data Set
• RRDS - Relative Record Data Set
5Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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
6Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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
7Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
8Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
9Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
10Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
11Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
12Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
13Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
14Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
Sequential access - Browsing• STARTBR
• READNEXT
• READPREV
• RESETBR
• ENDBR
15Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
STARTBR
• This establishes a browse session.
EXEC CICS STARTBR
FILE (‘EMPFILE’)
RIDFLD (EMP-REC-KEY)
KEYLENGTH(KEY-LEN)
GTEQ/EQUAL/GENERIC
END-EXEC.
16Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
READNEXT/READPREV
EXEC CICS READNEXT/READPREV
FILE (‘EMPFILE’)
INTO (EMP-REC)
LENGTH (EMP-REC-LEN)
RIDFLD (EMP-REC-KEY)
END-EXEC.
17Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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.
18Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
ENDBR
• End browse operation
EXEC CICS ENDBR
FILE (‘EMPFILE’)
END-EXEC.
19Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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
20Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
Temporary Storage
• COMMAREA (Communication Area)
• CWA (Common Work Area)
• TWA (Transaction Work Area)
• TSQ (Temporary Storage Queue)
• TDQ (Transient Data Queue)
21Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
TSQ Commands
• WRITEQ TS
EXEC CICS WRITEQ TS QUEUE (qname) FROM (recarea) LENGTH (length) option (option)…END-EXEC.
22Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
TSQ Commands
• READQ TS
EXEC CICS READQ TS
QUEUE (qname)
INTO (recarea)
LENGTH (length)
option
END-EXEC
23Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
TSQ Commands
• DELETEQ TS
EXEC CICS DELETEQ TS
QUEUE (qname)
END-EXEC.
24Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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
25Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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
26Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
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?
27Copyright © 2005, Infosys Technologies Ltd
ER/CORP/CRS/TP01/003 Version No: 1.0
Thank You!
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