Monday, August 13, 2012

Why oracle does not use my index ?

  • An index is unlikely to be used if the clustering factor is close to the number of rows unless the selectivity is very strong
  • The clustering of an index will not change if you rebuild the index
  • The clustering factor of an index will change if you rebuild the table so that the data is physicaly ordered by the index key
  • You cannot have a low clustering factor for two independent indexes of the same table

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