Causally Coordinated Snapshot Isolation for Geographically Replicated Data

We propose a Snapshot Isolation based transaction execution and consistency model, referred to as causally coordinated snapshot isolation, for geographically replicated data. The data replication is managed through asynchronous update propagation. Our approach provides snapshot-isolation model over multiple sites and ensures causal ordering of transactions. We present here an efficient protocol for precisely capturing the causal data dependencies of transactions and ensuring the causal ordering based on these dependencies when applying transactions' updates at remote sites. Through experimental evaluations, we demonstrate the benefit of this protocol over an alternative approach for providing causal consistency for georeplicated data. We further extend this model to support session consistency guarantees such as read-your-writes and monotonic reads. Additionally, we provide a notion of group-session where a group of users are involved in a collaborative session. We provide various group-session consistency guarantees for users collaborating in a group. We present the mechanisms for providing these session consistency guarantees and evaluate their performance.