c-Lock: Dynamic Lock-coalescing for Latency-sensitive Distributed Locking

Transactional updates to groups of keys are common to a wide class of distributed systems, spanning MapReduce-based workloads, distributed key-value stores and conventional distributed object databases. Such updates are typically implemented using nested transactions/ locks. The cost of such updates is critically dependent on the nesting depth, the contention on any one lock, and the coherence of key-groups. In this paper, we analyze techniques for coalescing key updates and associated locks to reduce nesting depth. Specifically, we demonstrate that in real workloads, the coherence of keygroup updates enables us to effectively coalesce locks to gain significant performance improvements. We prove our results through rigorous average case analysis, and support it using detailed simulations.