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DB2 9 for z/OS Performance Topics

(Paolo Bruni, Kevin Harrison, Garth Oldham, Leif Pedersen and Giuseppe Tino) DB2 9 for z/OS is an exciting new version, with many improvements in performance and very little regression. DB2 V9 improves availability, security and adds greatly to SQL and XML function. Optimization improvements include

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Redundant index is not always bad

(Vadim Tkachenko) About year ago Peter wrote about redundant indexes and mentioned sometimes it is good to leave two indexes, even one is first part of another. I’m speaking about BTREE indexes, for example, KEY (A), and KEY (A,B). From SQL point of view KEY(A) is not needed, as for queries like WHE