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E03 - Why Low-Cardinality Indexes Negatively Impact Performance

Topic: Cross Platform DB2 for z/OS & LUW

Subtopic: 2014



Tuning SQL via indexes is one skill any DBA must learn. Any DBA or developer will hear recommendations on indexing in DB2 databases for Linux, Unix and Windows; what to index, what not to index, how to analyze existing indexes, etcetera. One principle taught is that low cardinality indexes are bad. But why is that so? In this session, we will take a deep dive into why low-cardinality indexes are bad for performance. This presentation was given to several users groups in the midwest in fall of 2013, and received high ratings. It is refined and updated for IDUG 2014. Ember also wrote a developerWorks article on this topic: http://www.ibm.com/developerworks/data/library/techarticle/dm-1309cardinal/index.html



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