Middleware based data replication providing snapshot isolation

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.

Managing Multiple Isolation Levels in Middleware Database Replication Protocols

“…There have been multiple database replication protocols in the update everywhere server architecture with a constant server interaction [11,19,17,9,12,23]. Many of them share the following characteristics, proving to be extremely adequate for replication purposes.…”

“…Most current database replication protocols aim to provide support for only the serialisable [22,19,17] or snapshot isolation levels [9,12], since they are needed by a wide variety of applications. However, there have also been some works that have studied multiple levels of isolation, either providing protocols for each of them [11,23] or by specifying new definitions of such levels [4,2].…”

Pronto: High availability for standard off-the-shelf databases

“…Amza et al [13] introduces a database replication protocol that guarantees strong consistency Many works have considered alternative consistency criteria for database replication, such as Snapshot Isolation [8], and its variations for replicated settings [34,50]. Kemme et al discuss in [27] how to implement both serializability and snapshot isolation using group communication; all protocols presented require modifications to the database engine.…”

Reviewing Amnesia Support in Database Recovery Protocols

“…On one hand, performance can be improved when clients access the closest replica to them [24,25,23], or by using load-balancing algorithms [26,13,2]. On the other hand, replicas may fail or may disconnect; therefore, fault tolerance and high availability are reached forwarding client requests to non-failed nodes in a transparent way.…”

“…Latest trends in full database replication techniques -managed by replication protocols [24,25,23,26,13,2]-make use of a Group Communication System (GCS for short) [9] as it is detailed in [28]. These GCSs offer different services to the systems built atop of them.…”