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Q: How to tune DB2 queries?
Answer:
Check EXPLAIN output. Look at: access type (index vs scan), join method, sort operations. Add indexes for predicates. Rewrite with hints. Update statistics. Check for full tablespace scans. Monitor actual execution.
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Q: How to handle file status 22?
Answer:
Status 22 is duplicate key on WRITE or REWRITE attempt. KSDS primary key must be unique. Check program logic. May indicate data error. Use DUPLICATES option on AIX only if needed.
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Q: Explain REUSE parameter
Answer:
REUSE allows reloading without delete/define. DEFINE CLUSTER ... REUSE. OPEN OUTPUT resets to empty. Like scratch and rewrite. Good for temporary work files. Cannot be UNIQUE.
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Q: How to update KSDS record?
Answer:
READ record (optionally FOR UPDATE). Modify record area. REWRITE record. Key cannot change on REWRITE. Status 00 if successful. ACCESS MODE must allow updates.
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Q: How to WRITEQ with REWRITE?
Answer:
WRITEQ TS with REWRITE updates existing item. EXEC CICS WRITEQ TS QUEUE(name) FROM(data) REWRITE ITEM(n). Without REWRITE, adds new item. ITEM must exist for REWRITE.
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Q: Explain REWRITE command
Answer:
REWRITE updates record. Must READ with UPDATE first. EXEC CICS REWRITE FILE(name) FROM(data) LENGTH(len). Changes record held from READ. Cannot change key. TOKEN matches UPDATE-READ.