Evaluation of remote backup algorithms for transaction processing systems

A remote backup is a copy of a primary database maintained at a geographically separate location and is used to increase data availability. Remote backup systems are typically log-based and can be classified into 2-safe and 1-safe, depending on whether transactions commit at both sites simultaneously or they first commit at the primary and are later propagated to the backup. We have built an experimental database system on which we evaluated the performance of the epoch algorithm, a 1-safe algorithm we have developed, and compared it with the 2-safe approach under various conditions. We also report on the use of multiple log streams to propagate information from the primary to the backup.