The Impact of Timestamp Granularity in Optimistic Concurrency Control

TL;DR

This paper demonstrates that using fine-grained timestamp granularity in optimistic concurrency control significantly improves performance, surpassing advanced algorithms like TicToc in high-core environments.

Contribution

It reveals that timestamp granularity is a critical factor affecting OCC performance, showing simple modifications can outperform complex alternative mechanisms.

Findings

Fine-grained timestamps improve OCC throughput by 1.14x in TPC-C at 128 cores.

Traditional OCC can outperform TicToc with proper timestamp granularity.

Timestamp granularity impacts transaction processing performance more than previously recognized.

Abstract

Optimistic concurrency control (OCC) can exploit the strengths of parallel hardware to provide excellent performance for uncontended transactions, and is popular in high-performance in-memory databases and transactional systems. But at high contention levels, OCC is susceptible to frequent aborts, leading to wasted work and degraded performance. Contention managers, mixed optimistic/pessimistic concurrency control algorithms, and novel optimistic-inspired concurrency control algorithms, such as TicToc, aim to address this problem, but these mechanisms introduce sometimes-high overheads of their own. We show that in real-world benchmarks, traditional OCC can outperform these alternative mechanisms by simply adding fine-grained version timestamps (using different timestamps for disjoint components of each record). With fine-grained timestamps, OCC gets 1.14x TicToc's throughput in TPC-C at 128 cores (previous work reported TicToc having 1.8x higher throughput than OCC at 80 hyperthreads). Our study shows that timestamp granularity has a greater impact than previously thought on the performance of transaction processing systems, and should not be overlooked in the push for faster concurrency control schemes.