Middleware based Data Replication providing Snapshot Isolation Yi Lin, Bettina Kemme, Marta Patino-Martinez, and Ricardo Jimenez-Peris   View Paper (PDF)   Return to Correctness and Trust (Research) Abstract Many cluster based replication solutions have been proposed providing scalability and fault-tolerance. Many of these solutions perform replica control in a middleware on top of the database replicas. In such a setting concurrency control is a challenge and is often performed on a table basis. Additionally, some systems put severe requirements on transaction programs (e.g., to declare all objects to be accessed in advance). This paper addresses these issues and presents a middleware-based replication scheme which provides the popular snapshot isolation level at the same tuplelevel granularity as database systems like PostgreSQL and Oracle, without any need to declare transaction properties in advance. Both read-only and update transactions can be executed at any replica while providing data consistency at all times. Our approach provides what we call "1-copysnapshot-isolation" as long as the underlying database replicas provide snapshot isolation. We have implemented our approach as a replicated middleware on top of PostgreSQL replicas. By providing a standard JDBC interface, the middleware is completely transparent to the client program. Fault-tolerance is provided by automatically reconnecting clients in case of crashes. Our middleware shows good performance in terms of response times and scalability. ©2006 Association for Computing Machinery