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Q: When should I use COMMIT in DB2?
Answer:
COMMIT saves all changes since the last COMMIT and releases locks.
When to COMMIT:
- After processing a logical unit of work
- Periodically in long-running batch (every N records)
- Before ending the program successfully
Frequency Guidelines:
- Too frequent: Performance overhead
- Too rare: Lock contention, large log
- Typical: Every 100-1000 records in batch
Best Practice:
MOVE 0 TO WS-COMMIT-COUNT.
PERFORM PROCESS-RECORD.
ADD 1 TO WS-COMMIT-COUNT.
IF WS-COMMIT-COUNT >= 500
EXEC SQL COMMIT END-EXEC
MOVE 0 TO WS-COMMIT-COUNT
END-IF.
Note: In CICS, syncpoint (COMMIT) happens automatically at task end. Explicit SYNCPOINT is rarely needed.
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Q: Explain LOG parameter
Answer:
LOG(NONE/UNDO/ALL) specifies recovery logging. UNDO for backward recovery. ALL for forward and backward. NONE for no logging. Used with transactional systems. Most batch uses NONE.
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Q: How to handle VSAM in batch?
Answer:
Define cluster with IDCAMS. JCL DD statement references cluster. COBOL SELECT maps to DD. ACCESS MODE matches operations. Close properly. STATUS check after operations.
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Q: Explain NOTIFY parameter
Answer:
NOTIFY=userid sends message when job completes. On JOB card. Multiple userids: NOTIFY=(USER1,USER2). Notifies success or failure. TSO users get message at terminal. Essential for batch monitoring. Commonly NOTIFY=&SYSUID for submitter.
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Q: What causes S0C7 in batch?
Answer:
S0C7 is data exception - non-numeric in numeric field. Check: input file data quality, initialize variables, correct REDEFINES, field alignment. Use OFFSET in dump to find statement. LE CEEDUMP shows data values. Common with new programs.
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Q: What causes S0C4 in batch?
Answer:
S0C4 is protection exception - addressing unallocated memory. Causes: uninitialized pointer, subscript out of range, incorrect LINKAGE SECTION. Check CEEDUMP for offset. Likely program bug. Use debugger to trace.
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Q: Explain DD PATH statement?
Answer:
PATH specifies Unix/USS file. PATH='/u/user/file'. Used instead of DSN. PATHDISP for disposition. PATHOPTS for options. PATHMODE for permissions. Integrates USS files into batch JCL.
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Q: How to handle RLS (Record Level Sharing)?
Answer:
RLS allows VSAM access without exclusive control. Define with SHAREOPTIONS and LOG. Enable RLS at VSAM level. CF lock structure coordinates. Better than old batch/CICS conflicts.
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Q: How does ACCEPT and DISPLAY work?
Answer:
ACCEPT reads from console/system: ACCEPT WS-DATE FROM DATE, ACCEPT WS-INPUT FROM CONSOLE. DISPLAY writes to console: DISPLAY 'Message' WS-FIELD. UPON clause specifies destination. Limited in batch; mainly for debugging or simple interaction.
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Q: Explain thread management
Answer:
Thread is DB2 connection. Allied thread for TSO/batch. DBAT (database access thread) for DDF. Pool thread for efficient reuse. Max threads controlled by zparm. Monitor active threads.
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Q: How to handle multi-string access?
Answer:
STRNO parameter defines concurrent requests. More strings for high-activity files. Costs memory per string. JCL: AMP='STRNO=5'. Default usually 1. Batch usually needs 1-2.
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Q: How to access VSAM via CICS?
Answer:
Define FILE in CICS FCT (File Control Table). Or RDO DEFINE FILE. EXEC CICS READ FILE. VSAM must be closed to batch when CICS owns. NSRV or LSR buffering. BROWSE for sequential.
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Q: What is EXEC CICS SPOOLOPEN?
Answer:
SPOOLOPEN accesses JES spool. SPOOLREAD/SPOOLWRITE for data. SPOOLCLOSE ends. Process job output. Modern batch integration. Requires authorization.