Multilevel Index If index does not fit in memory,access becomes expensive. Solution:treat index kept on disk as a sequential file and construct a sparse index on it. outer index-a sparse index of the basic index inner index-the basic 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-7th Edition 14.12 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 14.12 ©Silberschatz, Korth and Sudarshan th Edition Multilevel Index ▪ If index does not fit in memory, access becomes expensive. ▪ Solution: treat index kept on disk as a sequential file and construct a sparse index on it. • outer index – a sparse index of the basic index • inner index – the basic 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