Creek: Low-latency, Mixed-Consistency Transactional Replication Scheme

Abstract

In this paper we introduce Creek, a low-latency, eventually consistent replication scheme that also enables execution of strongly consistent requests. Creek disseminates the messages among the replicas using only a gossip protocol. Similarly to state machine replication (SMR), Creek totallyorders all requests, but does so using two different mechanisms: a timestamp-based one and one built on top of our novel broadcast primitive, conditional atomic broadcast (CAB). The former is used to establish a tentative order of all requests for speculative execution and works also within each partition, when partitioning of network occurs. On the other hand, CAB is used only for the strongly consistent requests to ensure their linearizable execution, and is available whenever distributed consensus can be solved. The execution of a strongly consistent request also stabilizes the execution order of the causally related weakly consistent requests. Creek uses multiversion concurrency control to efficiently handle requests' rollbacks and reexecutions resulting from the mismatch between the tentative and the final execution orders. In the tests conducted using the TPC-C benchmark, Creek offers up to 3 times lower latency in returning client responses compared to the state-of-the-art speculative SMR scheme, while maintaining high accuracy of the speculative execution (92-100%).