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Q: How do I fix S0C7 Data Exception ABEND?
Answer:
S0C7 occurs when the program tries to perform arithmetic on non-numeric data.
Common Causes:
- Uninitialized numeric fields (contains spaces/garbage)
- Moving alphanumeric data to numeric field
- Reading file with wrong record layout
- Array subscript accessing wrong memory
How to Fix:
- Initialize all numeric fields to ZEROS
- Validate input before arithmetic
- Check file layouts match
- Use DISPLAY to debug field contents
* Always initialize
INITIALIZE WS-RECORD.
MOVE ZEROS TO WS-AMOUNT.
* Validate before use
IF WS-INPUT IS NUMERIC
COMPUTE WS-RESULT = WS-INPUT * 2
END-IF.
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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: What is RECOVER utility?
Answer:
RECOVER restores data from backup/logs. RECOVER TABLESPACE db.ts. Options: TOCOPY, TORBA, TOLOGPOINT. Image copy is backup. RECOVER applies logs to copy. Essential for disaster recovery.
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Q: What is RBA?
Answer:
RBA (Relative Byte Address) is byte offset from dataset start. ESDS uses RBA for access. KSDS index points to RBA. Changed by REORG. Use key for KSDS, RBA only when necessary.
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Q: What is HURBA?
Answer:
HURBA (High Used RBA) marks end of data. Records beyond HURBA are unused space. LISTCAT shows HURBA. Grows as records added. REORG resets to eliminate gaps in ESDS.
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Q: Explain RECOVERY vs NORECOVER?
Answer:
RECOVERY (default) enables recovery after abend. Writes RBA info to catalog. NORECOVER disables - cannot recover from abend. NORECOVER saves some overhead but risky.
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Q: Explain referback DD
Answer:
Referback references earlier DD: DSN=*.STEP1.DDNAME or DSN=*.DDNAME (same step). Copies DSN and DISP. Can override other parameters. VOL=REF=*.STEP1.DD copies volume. Useful for chained processing.
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Q: How to define ESDS?
Answer:
DEFINE CLUSTER(NAME(ds.name) NONINDEXED RECORDSIZE(avg max)) DATA(NAME(ds.data) CYLINDERS(10 2)). NONINDEXED means ESDS. No KEYS or INDEX components. Access by RBA only.