Validation-Based Protocols
In optimistic concurrency control techniques, also known as Validation or certification techniques, no checking is done while transaction is executing.
It has three phases
ü Read phase
ü Write phase
ü Validation phase
Read phase-: during this phase, the system executes Transaction Ti. It read the value of the various data items and stores them in variable local to Ti. It perform all the write operation on temporary local variables without update of the actual database.
Write phase-: If transaction is Ti succeeds in validation, then the system applies the actual update to the database, otherwise the system rolls back Ti.
Validation phase-: Transaction Ti perform a validation test to determine whether it can copy to database the temporary local variable that hold the result of write operation without causing a violation of serializability.
To perform the validation test, we need to know when the various phases of transactions Ti took place.
1. Start (Ti), the time when Ti start its execution.
2. Validation (Ti), the time when Ti finish its reading phase and started its validation phase.
3. Finish (Ti), the time when Ti finish its writing phase.
