Transaction Concept A transaction is a unit of program execution that accesses and possibly updates various data items. E.g.,transaction to transfer $50 from account A to account B: 1.read(A) 2.A=A-50 3.write(A) 4.read(B) 5.B=B+50 6.write(B) Two main issues to deal with: Failures of various kinds,such as hardware failures and system crashes Concurrent execution of multiple transactions Database System Concepts-6th Edition 14.3 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 14.3 ©Silberschatz, Korth and Sudarshan th Edition Transaction Concept A transaction is a unit of program execution that accesses and possibly updates various data items. E.g., transaction to transfer $50 from account A to account B: 1. read(A) 2. A := A – 50 3. write(A) 4. read(B) 5. B := B + 50 6. write(B) Two main issues to deal with: Failures of various kinds, such as hardware failures and system crashes Concurrent execution of multiple transactions