Multiple Granularity Allow data items to be of various sizes and define a hierarchy of data granularities,where the small granularities are nested within larger ones Can be represented graphically as a tree(but don't confuse with tree- locking protocol) When a transaction locks a node in the tree explicitly,it implicitly locks all the node's descendents in the same mode. Granularity of locking (level in tree where locking is done): fine granularity (lower in tree):high concurrency,high locking overhead coarse granularity (higher in tree):low locking overhead,low concurrency Database System Concepts-5th Edition,Oct 5,2006 16.19 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 16.19 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Multiple Granularity Allow data items to be of various sizes and define a hierarchy of data granularities, where the small granularities are nested within larger ones Can be represented graphically as a tree (but don't confuse with tree￾locking protocol) When a transaction locks a node in the tree explicitly, it implicitly locks all the node's descendents in the same mode. Granularity of locking (level in tree where locking is done): fine granularity (lower in tree): high concurrency, high locking overhead coarse granularity (higher in tree): low locking overhead, low concurrency