#  > Engineering Notes - Handwritten Notes of all Engineering branches >  > Computer Science and Engineering Notes >  >  Validation-Based Protocols in database management system free pdf notes

## amitsharma957

Each transaction Ti executes in two or three different  phases in its lifetime, depending on whether it is a read-only or an  update transaction. The phases are, in order,  	*1. Read phase*. During this phase, the system executes transaction Ti. It reads the values of the various data items and stores them in variables local to Ti. It performs all write operations on temporary local variables, without updates of the actual database.

*2. Validation phase*. Transaction Ti  performs a validation test to determine whether it can copy to the  database the temporary local variables that hold the results of write  operations without causing a violation of serializability.

*3. Write phase*. If transaction Ti succeeds in validation (step 2), then the system applies the actual updates to the database. Otherwise, the system rolls back
	Ti.





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