A column-store database management system (DBMS) is a DBMS that indexes each column of a table, storing the indexes in lieu of row data — unlike traditional relational DBMSs using a row-store, where data is stored in rows, with indexes optional. In addition, most column-store DBMSs include additional optimization techniques (such as compression and tokenization) to further compress the data — using less storage and increasing input/output (I/O) performance. We do not include row-store DBMS engines that offer columnar forms of compression only.