To tune index usage, it’s important to understand the various types of index access paths available to the cost optimizer. This chapter summarizes the most important index access paths available to the optimizer. Often, Oracle database administrators are bewildered when the optimizer chooses not to use what they believe is a very useful index, but does a full table scan instead. This chapter devotes attention to exploring some reasons why the optimizer might prefer a full table scan to using an index. You’ll also learn how to force the optimizer to use (or not to use) an index. Oracle provides a large number of index-related hints to enable you to control the behavior of the optimizer regarding index usage. You’ll find descriptions of the key index-related hints in this chapter.