Tuesday, August 14, 2012

When to create Bitmap Indexes

  • When a table has millions of rows and the key columns have low cardinality—that is, there are very few distinct values for the column. For example, bitmap indexes may be preferable to B-tree indexes for the gender and marital status columns of a table containing passport records
  • When queries often use a combination of multiple WHERE conditions involving the OR operator
  • When there is read-only or low update activity on the key columns

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