Mastering Database Management

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Concurrency Control Techniques

Timestamp based Protocol

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  • Lock-based protocols manage the order between the conflicting pairs among transactions at the time of execution, whereas timestamp-based protocols start working as soon as a transaction is created.
  • Every transaction has a timestamp associated with it, and the ordering is determined by the age of the transaction.
  • A transaction created at 0002 clock time would be older than all other transactions that come after it. For example, any transaction ‘y’ entering the system at 0004 is two seconds younger and the priority would be given to the older one.
  • In addition, every data item is given the latest read and write-timestamp. This lets the system know when the last ‘read and write’ operation was performed on the data item.

Timestamp Ordering Protocol

 The timestamp-ordering protocol ensures serializability among transactions in their conflicting read and write operations. This is the responsibility of the protocol system that the conflicting pair of tasks should be executed according to the timestamp values of the transactions.

  • The timestamp of transaction Ti is denoted as TS(Ti).
  • Read timestamp of data-item X is denoted by R-timestamp(X).
  • Write timestamp of data-item X is denoted by W-timestamp(X)

Timestamp ordering protocol works as follows −