What can you achieve by implementing reverse key index?
A.
Reverse the bytes of each column indexed including the row ID
B.
Store a bitmap for each key value instead of a list of row IDs in the leaf node
C.
Prevent contention on the highest leaf block when using sequences to generate keys
D.
Remove repeated key values from the index to fit more index entries in a given amount of disk
space
A Reverse Key Index simply takes the index column values and reverses them before inserting into the index. “Conceptually”, say the next generated ID is 123456, Oracle will reverse it to 654321 before inserting into the index. It will then take the next generated ID 123457 and reverse it to 754321 and insert it into the index and so on. By doing this, inserts are spread across the whole index structure, ensuring the right most block is no longer the only index leaf block being hammered. Index contention is dramatically reduced or eliminated entirely.
Reverse Key Indexes are designed to resolve index block contention.