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Q: What is the difference between KSDS and ESDS?
Answer:
KSDS (Key Sequenced Data Set):
- Records accessed by unique key
- Records stored in key sequence
- Has both data and index components
- Supports random and sequential access
- Can delete and reinsert records
- Most commonly used VSAM type
ESDS (Entry Sequenced Data Set):
- Records stored in arrival order
- Accessed by RBA (Relative Byte Address)
- No index component
- Cannot delete records (only mark inactive)
- Similar to sequential files
- Good for logs, audit trails
Use KSDS when: You need key-based access, updates, deletes
Use ESDS when: Sequential processing only, append-only data
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Q: Explain DB2 triggers
Answer:
Trigger fires automatically on INSERT/UPDATE/DELETE. CREATE TRIGGER name AFTER/BEFORE/INSTEAD OF event ON table FOR EACH ROW/STATEMENT. Use for audit, validation, derived columns. Can impact performance.
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Q: What is ASSIGN command?
Answer:
ASSIGN retrieves system values. EXEC CICS ASSIGN USERID(ws-user) FACILITY(ws-term). Other options: SYSID, ABCODE, PROGRAM. Gets runtime environment info. Useful for audit, conditional processing.
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Q: What is journaling in CICS?
Answer:
Journaling records activity. EXEC CICS JOURNAL JFILEID(id) FROM(data). For recovery, audit. Define journal file. Can be automatic or explicit. System journal for CICS recovery.