The difference between Oracle index unusable and invisible

Excerpts from the official documents of 11g:

     unusable  specify unusable to mark the index or index partition (s) or index subpartition (s) UNUS ABLE. The space allocated for a index or index partition or subpartition is freed immediately when the object is marked UNUSABL E. An unusable index must is rebuilt, or dropped and re-created, before it can be used. While one partition was marked unusable, the other partitions of the index was still valid. You can execute statements that require the index if the statements does not access the unusable partition. You can also split or rename the unusable partition before rebuilding it. Refer to CREATE INDEX ... Unusable for more information.

An index, which is not a maintained by DML operations and was ignored by the optimizer. All indexes is usable (default) or unusable.

VISIBLE | INVISIBLE Use this clause to specify whether the index are visible or INVISIBLE to the optimizer. An invisible index was maintained by DML operations, but it was not being used by the optimizer during queries unless you expli citly set the parameter optimizer_use_invisible_indexes to TRUE on the session or system level.

unusable index is ignored by the optimizer and is not maintained by DML operations, assuming the index is unusable. Need to be rebuilt.

The invisible index is ignored by the optimizer, but the DML operation still maintains the index. use parameters at session or system level Optimizer_use_invisible_indexes=true. Then the optimizer will consider using invisible index. Applies to see if the index is being used.

The difference between Oracle index unusable and invisible