Releasing Locks As Early As You Can: Reducing Contention of Hotspots by Violating Two-Phase Locking (Extended Version)

TL;DR

This paper introduces Bamboo, a concurrency control protocol that reduces contention by releasing locks early, allowing parallelism during hotspots, and achieves significant performance improvements over traditional methods.

Contribution

Bamboo is a novel protocol that violates two-phase locking to enable early lock release during hotspots while maintaining correctness.

Findings

Up to 4x performance improvement on TPC-C.

Up to 19x speedup on synthetic hotspot workloads.

Effective reduction of contention and increased parallelism.

Abstract

Hotspots, a small set of tuples frequently read/written by a large number of transactions, cause contention in a concurrency control protocol. While a hotspot may comprise only a small fraction of a transaction's execution time, conventional strict two-phase locking allows a transaction to release lock only after the transaction completes, which leaves significant parallelism unexploited. Ideally, a concurrency control protocol serializes transactions only for the duration of the hotspots, rather than the duration of transactions. We observe that exploiting such parallelism requires violating two-phase locking. In this paper, we propose Bamboo, a new concurrency control protocol that can enable such parallelism by modifying the conventional two-phase locking, while maintaining the same guarantees in correctness. We thoroughly analyzed the effect of cascading aborts involved in reading uncommitted data and discussed optimizations that can be applied to further improve the performance. Our evaluation on TPC-C shows a performance improvement up to 4x compared to the best of pessimistic and optimistic baseline protocols. On synthetic workloads that contain a single hotspot, Bamboo achieves a speedup up to 19x over baselines.