Database Systems: Concepts, Design and Applications

12.5. Timestamp Methods for Concurrency Control

Timestamp is a unique identifier created by the DBMS to identify the relative starting time of a transaction. Typically, timestamp values are assigned in the order in which the transactions are submitted to the system. So, a timestamp can be thought of as the transaction start time. Therefore, time stamping is a method of concurrency control in which each transaction is assigned a transaction timestamp. A transaction timestamp is a monotonically increasing number, which is often based on the system clock. The transactions are managed so that they appear to run in a timestamp order. Timestamps can also be generated by incrementing a logical counter every time a new transaction starts. The timestamp ...