Lazy database replication with snapshot isolation

Abstract

Snapshot isolation is a popular transactional isolation level in database systems. Several replication techniques based on snapshot isolation have recently been proposed. These proposals, however, do not fully leverage the local concurrency controls that provide snapshot isolation. Furthermore, guaranteeing snapshot isolation in lazy replicated systems may result in transaction inversions, which happen when transactions see stale data. Strong snapshot isolation, which is provided in centralized database servers, avoids transaction inversions but is expensive to provide in a lazy replicated system. In this paper, we show how snapshot isolation can be maintained in lazy replicated systems while taking full advantage of the local concurrency controls. We propose strong session snapshot isolation, a correctness criterion that prevents transaction inversions. We show how strong session snapshot isolation can be implemented efficiently in a lazy replicated database system. Through performance studies, we quantify the cost of implementing our techniques in lazy replicated systems.