Bonspiel: Low Tail Latency Transactions in Geo-Distributed Databases

Tail latency is crucial as it impacts user satisfaction and service-level objectives (SLOs). However, geo-distributed databases have long struggled with this issue due to wide-area network access, resulting in tail latencies of several or even exceeding ten seconds. In this paper, we highlight that further optimizing atomic commit protocols does not help but hit a tail latency wall. Instead, making concurrency control and access method selection geo-aware can mitigate this issue. To this end, we present Bonspiel, a new geo-distributed database equipped with geo-aware concurrency control and access method selection. In our experiments, Bonspiel successfully caps the tail latency of TPC-C at 1.8 seconds. Remarkably, it achieves this while maintaining full generality - it is fully SQL-compliant and strongly consistent, with both average latency and system throughput remaining at the top of the field.