Thus far, you’ve learned how to create normal Oracle indexes, which include both B-tree indexes as well as bitmap indexes. You also learned how to create and manage index organized tables. This chapter explains several specialized indexes that you can create for serving various needs. Most of these specialized indexes are actually B-tree indexes, so it’s not the organization of the index that makes them special. For example, an invisible index is an index that’s not automatically available to the cost-based optimizer, unless you make it available by setting a specific initialization parameter. You use invisible indexes mainly for testing the use of an index and to make sure that an index is redundant before you drop it.