Rules for Transforming Order Dependent Transaction into Order Independent Transaction*
Department of Computer Science, Universiti Putra Malaysia, Malaysia
Abstract: A transaction is a collection of operations that performs a single logical function in a database application. Each transaction is a unit of both atomicity and consistency. Thus, transactions are required not to violate any database consistency constraints. In most cases, the update operations in a transaction are executed sequentially. The effect of a single operation in a transaction potentially may be changed by another operation in the same transaction. This implies that the sequential execution sometimes does some redundant work. A transaction with a set of update operations is order dependent if and only if the execution of the transaction following the serialibility order as in the transaction produce an output which will be different from the output produced by interchanging the operations in the transaction. Otherwise, the transaction is order independent . In this paper, we present rules that can be applied to generate order independent transaction given an order dependent transaction. An order independent transaction has an important advantage of its update statements being executed in parallel without considering their relative execution orders. With an order independent transaction, we can consider its single updates in an arbitrary order. Furthermore, executing transaction in parallel can reduce the execution time.
Keywords: Transaction, parallel processing, transaction decomposition, subtransaction, update operations.
Received March 2, 2004; accepted June 29, 2004