Handling of Skew The distribution of tuples to disks may be skewed -that is,some disks have many tuples,while others may have fewer tuples. Types of skew: Attribute-value skew. Some values appear in the partitioning attributes of many tuples;all the tuples with the same value for the partitioning attribute end up in the same partition. Can occur with range-partitioning and hash-partitioning Partition skew. With range-partitioning,badly chosen partition vector may assign too many tuples to some partitions and too few to others. Less likely with hash-partitioning if a good hash-function is chosen. Database System Concepts-6th Edition 18.12 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 18.12 ©Silberschatz, Korth and Sudarshan th Edition Handling of Skew The distribution of tuples to disks may be skewed — that is, some disks have many tuples, while others may have fewer tuples. Types of skew: Attribute-value skew.  Some values appear in the partitioning attributes of many tuples; all the tuples with the same value for the partitioning attribute end up in the same partition.  Can occur with range-partitioning and hash-partitioning. Partition skew.  With range-partitioning, badly chosen partition vector may assign too many tuples to some partitions and too few to others.  Less likely with hash-partitioning if a good hash-function is chosen