Unique Secondary Indexes and Performance
USIs provide alternate access paths.
Statistics play an important part in optimizing access when USIs define conditions for the following operations.
Because of the additional overhead for index maintenance, USI values should not change frequently. When you change the value of a secondary index, Teradata Database must undertake the following maintenance operations.
1 Delete secondary index references to the current value.
2 Generate secondary index references to the new value.
The same considerations apply to NUSIs.