Statistics play an important part in optimizing access when USIs define conditions for the following operations.
- Joining tables
- Satisfying WHERE predicates that specify comparisons, string matching, or complex conditionals
- Satisfying LIKE expressions
- Processing aggregates
Because of the additional overhead for index maintenance, USI values must not change frequently. When you change the value of a secondary index, Vantage must undertake the following maintenance operations.
- Delete secondary index references to the current value.
- Generate secondary index references to the new value.