An Optimized Two-Safe Approach to Maintaining Remote Backup Systems

In a remote backup system, transaction processing takes place at the primary and the log records generated at the primary are propagated to the remote backup which uses them to reconstruct a recent state of the database at the primary. In the event of a primary failure, the backup system takes over transaction processing without causing users to observe a breach in service. Existing remote backup algorithms can be classi ed as either 2-safe or 1-safe based on whether or not the commitment of the transaction at the primary is synchronized with the propagation of its log records to the backup. Both approaches have limitations. While 1-safe approaches o er higher primary system throughput and lower transaction response time, unlike 2-safe approaches, they do not guarantee persistence of transactions during backup takeover. In this paper, we present an optimized 2-safe approach to maintaining remote backup systems that combines the desirable features of both 1-safe and 2-safe approaches { high throughput (similar to 1-safe) without risking the loss of transactions (similar to 2-safe). Algorithms are developed for multiple processor primary and backup system environments.