The number of lines per index descriptor block (IDB), as defined in the default, is set to five for all streams. You can decrease the number of IDBs created by increasing the number of lines per IDB. The net result is a decrease in the amount of overhead (less storage for IDBs), but an increase in search time when scrolling through a stream. Decreasing the number of lines per IDB increases the total number of IDBs and the storage required for them. But the efficiency of stream accessing improves when there are fewer lines per IDB.

For a discussion about calculating the number of IDBs, see Stream size.