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Validation Based Protocol

Validation phase is also known as optimistic concurrency control technique. In the validation based protocol, the transaction is executed in the following three phases:

  1. Read phase: In this phase, the transaction T is read and executed. It is used to read the value of various data items and stores them in temporary local variables. It can perform all the write operations on temporary variables without an update to the actual database.
  2. Validation phase: In this phase, the temporary variable value will be validated against the actual data to see if it violates the serializability.
  3. Write phase: If the validation of the transaction is validated, then the temporary results are written to the database or system otherwise the transaction is rolled back.

Here each phase has the following different timestamps:

Start(Ti): It contains the time when Ti started its execution.

Validation (Ti): It contains the time when Ti finishes its read phase and starts its validation phase.

Finish(Ti): It contains the time when Ti finishes its write phase.

  • This protocol is used to determine the time stamp for the transaction for serialization using the time stamp of the validation phase, as it is the actual phase which determines if the transaction will commit or rollback.
  • Hence TS(T) = validation(T).
  • The serializability is determined during the validation process. It can't be decided in advance.
  • While executing the transaction, it ensures a greater degree of concurrency and also less number of conflicts.
  • Thus it contains transactions which have less number of rollbacks.





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