Index blocks have the same header information as data blocks, and have the same size requirements of 16 bytes for Type I storage areas, and 64 or 80 bytes for Type II storage areas. Index blocks can store the amount of information that can fit within the block, and that information is compressed for efficiency. As stated earlier, index blocks can only contain information referring to a single index.

Indexes are used to find records in the database quickly. Each index in an OpenEdge RDBMS is a structured B-tree and is always in a compressed format. This improves performance by reducing key comparisons. A database can have up to 32,767 indexes. Each B-tree starts at the root. The root is stored in an _storageobject record. For the sake of efficiency, indexes are multi-threaded, allowing concurrent access. Rather than locking the whole B-tree, only those nodes that are required by a process are locked.