Introduction Parallel machines are becoming quite common and affordable Prices of microprocessors,memory and disks have dropped sharply Recent desktop computers feature multiple processors and this trend is projected to accelerate Databases are growing increasingly large large volumes of transaction data are collected and stored for later analysis. multimedia objects like images are increasingly stored in databases Large-scale parallel database systems increasingly used for: storing large volumes of data processing time-consuming decision-support queries providing high throughput for transaction processing Database System Concepts-5th Edition,Aug 22,2005. 21.3 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 21.3 ©Silberschatz, Korth and Sudarshan th Edition, Aug 22, 2005. Introduction Parallel machines are becoming quite common and affordable Prices of microprocessors, memory and disks have dropped sharply Recent desktop computers feature multiple processors and this trend is projected to accelerate Databases are growing increasingly large large volumes of transaction data are collected and stored for later analysis. multimedia objects like images are increasingly stored in databases Large-scale parallel database systems increasingly used for: storing large volumes of data processing time-consuming decision-support queries providing high throughput for transaction processing