c-tree supports another mechanism to distinguish among key values. The ISAM-level segment mode 3, SRLSEG, indicates that the key segment will automatically be filled with a 4-byte, ever increasing sequence number. Each time a record is added to the file, the sequence number is incremented. Instead of specifying that the index supports duplicates, the index can be set for unique keys and a 4-byte segment defined as part of the key with a segment mode of 3.
Unlike the duplicate key approach above, this approach DOES require that a 4-byte region of the file be reserved for the sequence number which c-tree will automatically initialize.