Multilevel Index If primary index does not fit in memory,access becomes expensive Solution:treat primary index kept on disk as a sequential file and construct a sparse index on it. outer index-a sparse index of primary index inner index-the primary index file If even outer index is too large to fit in main memory,yet another level of index can be created,and so on. Indices at all levels must be updated on insertion or deletion from the file. Database System Concepts-5th Edition,Oct 4,2006 12.9 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 12.9 ©Silberschatz, Korth and Sudarshan th Edition, Oct 4, 2006 Multilevel Index If primary index does not fit in memory, access becomes expensive. Solution: treat primary index kept on disk as a sequential file and construct a sparse index on it. outer index – a sparse index of primary index inner index – the primary index file If even outer index is too large to fit in main memory, yet another level of index can be created, and so on. Indices at all levels must be updated on insertion or deletion from the file