Fault Tolerant Data Management for Cloud Services

ABSTRACT

Database systems are the cornerstones of today’s information systems. The availability of database systems largely determines the quality of service provided by the information systems. In this chapter, the authors provide a brief overview of the state-of-the-art database replication and clustering techniques. For many, a low-cost shared-nothing database cluster that uses conventional hardware might be a good starting point towards high availability. The authors envisage that future generation of database management systems will be intrusion tolerant (i.e., they are capable of continuous operation against not only hardware and process crash fault but a variety of security threats as well).

Keywords: Database Cluster, Database Recovery, Database Replication, High Availability, NoSQL database, Transaction, Two-Phase Commit Protocol

Background

A database management system consists of a set of data and a number of processes that manage the data. These processes are often collectively referred to as database servers. The core programming model used in database management systems is called transaction processing. In this programming model, a group of read and write operations on the some data set are demarcated within a transaction. A transaction has the following ACID properties (Gray & Reuter, 1993):

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  Atomicity: All operations on the data set agree on the same outcome. Either all the operations succeed (the transaction commits), or none of them are (the transaction aborts).

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  Consistency: If the database is consistent at the beginning of a transaction, then the database remains consistent after the transaction commits.

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  Isolation: A transaction does not read or overwrite a data item that has been accessed by another concurrent transaction.

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  Durability: The update to the data set becomes permanent once the transaction is committed.