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Q: Explain STRING and UNSTRING operations
Answer:
STRING concatenates multiple fields into one: STRING field-1 DELIMITED BY SPACE field-2 INTO output-field. UNSTRING splits one field into multiple: UNSTRING input-field DELIMITED BY ',' INTO field-1 field-2. Both support POINTER for position tracking and OVERFLOW handling.
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Q: Explain FREESPACE parameter
Answer:
FREESPACE(cipct capct). CI percent free for inserts. CA percent free for splits. FREESPACE(20 10) leaves 20% CI, 10% CA free. More freespace reduces splits but uses more space. Tune based on activity.
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Q: How to improve KSDS performance?
Answer:
Appropriate CISIZE, FREESPACE. Adequate buffers (BUFND/BUFNI). Index in cache if possible. IMBED obsolete. Keep file organized (REORG). Monitor CA/CI splits. Sequential access for bulk.
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Q: Explain MASSINSERT?
Answer:
MASSINSERT optimizes bulk sequential inserts. System defers CI splits. Better performance for loads. Implicit with REPRO. COBOL can hint with APPLY WRITE-ONLY style.
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Q: What is FREESPACE distribution?
Answer:
FREESPACE spread across CIs and CAs. Initial load distributes evenly. After activity, distribution varies. REORG restores even distribution. Monitor CI/CA splits for tuning.
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Q: How to monitor VSAM performance?
Answer:
SMF records for I/O counts. LISTCAT for statistics (READS, WRITES, SPLITS). RMF reports. Third-party tools. Track CI/CA splits, EXCP counts, buffer hit ratios.