MODIFIED DOUBLE SPACE COMMIT PROTOCOL FOR DISTRIBUTED REAL-TIME DATABASE SYSTEMS

Abstract

Real-Time Database (RTDB) system can be -viewed as an amalgamation of a conventional Database Management System (DBMS) and a real-time system. Like a DBMS, it has to process transactions and guarantee basic correctness criteria. Furthermore it has to operate in real-time, satisfying timing constraints imposed on transaction commitments and on the temporal validity of data [21]. The work in this dissertation has been done in the context of real-time applications that impose 'firm deadlines" for transaction completion. There are several factors that contribute to the difficulty in meeting the transactions deadlines. One of the major factors is the data conflict between executing-committing transactions. This data conflict introduces the dependency between the transactions. Due to this dependency the dependent transaction waits for the subordinate transaction to commit in order to maintain ACID semantics in distributed data. Since the duration of commit phase is unpredictable due to delay in communication and system failures, the dependent transaction can miss its deadline while waiting for commitment of the transaction on which it is dependent. Therefore, design of a better real-time commit protocol is of great importance today. We present a new model of distributed transaction and analyze all kinds of dependencies that arise due to data conflicts in executing-committing mode of transaction operations. On the basis of these discussions, this dissertation identifies the shortcomings of the double space commit (2SC), a high performance distributed real-time commit protocol [4] for distributed real-time database systems and proposes suitable modification in it. The modified protocol reduces the data inaccessibility at the expense of some messages. However, it improves the system performance to a great extent.