There are several instances when you should consider creating EVIs.
Encoded vector indexes should be considered when any one of the
following is true:
- You want to gather 'live' statistics
- Full table scan is currently being selected for the query
- Selectivity of the query is 20%-70% and using skip sequential access with
dynamic bitmaps will speed up the scan
- When a star schema join is expected to be used for star schema join queries.
- When grouping or distinct queries are specified against a column, the
columns has a small number of distinct values and (if a column function is
specified at all) only the COUNT column function is used.
Encoded vector indexes should be created with:
- Single key columns with a low number of distinct values expected
- Keys columns with a low volatililty (they don't change often)
- Maximum number of distinct values expected using the WITH n DISTINCT VALUES
clause
- Single key over foreign key columns for a star schema model
