Some index tuning requires familiarity with the following
concepts: row filtering, property skew,
and composite indexes.
Row filtering
A query uses a primary property index to retrieve those
rows that potentially match the search conditions of the query. The
phrase row filtering refers to the work that is required
to determine whether a retrieved row matches all search conditions.
Property skew
When most but not all rows in the table have the same value
for a property, the column values are skewed. Property skew might
cause a query not to use a database index.
Composite indexes
A composite index is composed of multiple columns. These
columns can be a mixture of user-defined and system-defined properties
or be entirely of one type.