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Q: What is UDF (User Defined Function)?
Answer:
UDF extends SQL with custom functions. CREATE FUNCTION name(params) RETURNS type AS BEGIN logic END. Scalar returns single value. Table function returns rows. Use in SELECT, WHERE like built-in functions.
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Q: How to extend VSAM file?
Answer:
ALTER ds.name ADDVOLUMES(vol). Or secondary allocation triggers extension. RECORDS/CYLINDERS secondary amount. Up to 255 extents per volume. May need to reorganize if fragmented.
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Q: How to compress VSAM?
Answer:
DFSMS compression via DATACLAS. Or EXTENDED FORMAT with compression. Not native VSAM feature. Reduces space, adds CPU overhead. Good for large, read-heavy files.
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Q: What is RLSE subparameter?
Answer:
RLSE releases unused space at close. SPACE=(CYL,(10,5),RLSE). Returns unused secondary allocations. Good practice for new datasets. Saves disk space. May cause allocation issues if reextended.
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Q: What is OPEN mode options?
Answer:
OPEN INPUT for read, OUTPUT for write (creates), I-O for read/update, EXTEND for append. Multiple files per OPEN. OPEN OUTPUT deletes existing file! EXTEND preserves and adds. File must be closed before reopening in different mode.
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Q: Explain DFSORT utility
Answer:
DFSORT sorts/merges files. SYSIN has SORT FIELDS=(1,10,CH,A). SORTIN=input, SORTOUT=output. Options: INCLUDE/OMIT for filtering, OUTREC/INREC for reformatting, SUM for summarization. ICETOOL provides extended functions.
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Q: How to handle multivolume datasets?
Answer:
VOL=(,,,n) allows n volumes. SPACE with volume count. SMS handles multivolume automatically. DISP=MOD extends to new volume. DATACLAS can specify multivolume. Large datasets need multivolume planning.
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Q: What causes S837 abend?
Answer:
S837 is end of volume and no more volumes available. Dataset needs more space. Solutions: allocate larger primary/secondary, increase volume count, extend dataset. IEFBR14 can extend with MOD DISP.