I/O Parallelism Reduce the time required to retrieve relations from disk by partitioning the relations on multiple disks,on multiple nodes (computers) Our description focuses on parallelism across nodes Same techniques can be used across disks on a node Horizontal partitioning-tuples of a relation are divided among many nodes such that some subset of tuple resides on each node. Contrast with vertical partitioning,e.g.r(A,B,C,D)with primary key A into r1(A,B)and r2(A,C,D) By default,the word partitioning refers to horizontal partitioning Database System Concepts-7th Edition 21.4 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 21.4 ©Silberschatz, Korth and Sudarshan th Edition I/O Parallelism ▪ Reduce the time required to retrieve relations from disk by partitioning the relations on multiple disks, on multiple nodes (computers) • Our description focuses on parallelism across nodes • Same techniques can be used across disks on a node ▪ Horizontal partitioning – tuples of a relation are divided among many nodes such that some subset of tuple resides on each node. • Contrast with vertical partitioning, e.g. r(A,B,C,D) with primary key A into r1(A,B) and r2(A,C,D) • By default, the word partitioning refers to horizontal partitioning