Reverse Index: a reverse index is an index of keywords which stores records of documents that contain the keywords in the list. Database management systems provide a number of types of indexes to complete a wide variety of tasks, including bitmaps, r-trees, and b-trees. A reverse index is a version of a b-tree index, and is particularly useful when it comes to indexing sequence numbers and high volume processing systems.
Unlike other b-tree structures, reverse indexes process key values before inserting them into the index. By reversing these steps, the index spreads new values across the entire system instead of concentrating them in a set order. This means the index can operate without slowing down when multiple users attempt to insert values at the same time, as it doesn't have to classify the new information according to a set order. This is a common problem in other indexes, particularly clustered databases, which requires the system to copy the current database from another computer's memory before allowing a new user to enter values. However, reverse indexes are primarily used for finding specific values, and are therefore less helpful for range queries. This typically is not an issue, as sequence numbers and other values are unlikely to subjected to such a search.