Bitmap Indices (Cont.) Bitmap indices generally very small compared with relation size .E.g.,if record is 100 bytes,space for a single bitmap is 1/800 of space used by relation. If number of distinct attribute values is 8,bitmap is only 1%of relation size Deletion needs to be handled properly Existence bitmap to note if there is a valid record at a record location Needed for complementation not(A=v):(NOT bitmap-A-v)AND ExistenceBitmap Should keep bitmaps for all values,even null value To correctly handle SQL null semantics for NOT(A=V): intersect above result with (NOT bitmap-A-Null) Database System Concepts-7th Edition 24.14 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 24.14 ©Silberschatz, Korth and Sudarshan th Edition Bitmap Indices (Cont.) ▪ Bitmap indices generally very small compared with relation size • E.g., if record is 100 bytes, space for a single bitmap is 1/800 of space used by relation. ▪ If number of distinct attribute values is 8, bitmap is only 1% of relation size ▪ Deletion needs to be handled properly • Existence bitmap to note if there is a valid record at a record location • Needed for complementation ▪ not(A=v): (NOT bitmap-A-v) AND ExistenceBitmap ▪ Should keep bitmaps for all values, even null value • To correctly handle SQL null semantics for NOT(A=v): ▪ intersect above result with (NOT bitmap-A-Null)