DB2 ⭐ Featured
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Q: Explain VIEW creation

Answer:
VIEW is saved query. CREATE VIEW name AS SELECT... WITH CHECK OPTION enforces WHERE on updates. Can be updatable if simple. Views for security, simplification. Materialized views (MQT) store data.
view create virtual
COBOL
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Q: What is SERVICE RELOAD?

Answer:
SERVICE RELOAD refreshes segmented program overlays. Forces segment reload from disk. Rarely needed with virtual storage. From overlay management era. May affect performance. Better to restructure program than use frequently.
service reload segments
VSAM
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Q: What is LINEAR dataset?

Answer:
LINEAR VSAM is byte-addressable. No record structure. Used by DB2 tablespaces, system software. DEFINE CLUSTER LINEAR. Accessed via DIV (Data-in-Virtual) or memory mapping.
linear byte-addressable special
JCL
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Q: What is UNIT parameter?

Answer:
UNIT specifies device type. UNIT=SYSDA (direct access), UNIT=TAPE, UNIT=3390. UNIT=AFF=ddname shares device. UNIT=(SYSDA,2) allocates 2 volumes. SMS may override. UNIT=VIO for virtual I/O (memory only).
unit device allocation
DB2
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Q: What is DB2 buffer pool?

Answer:
Buffer pool caches data/index pages in memory. BP0, BP1, etc. Hit ratio critical for performance. GETPAGE vs SYNCIO shows effectiveness. Size appropriately. Virtual buffer pool for each pool. Monitor with statistics.
buffer-pool cache performance