Jiffy: A Lock-free Skip List with Batch Updates and Snapshots

TL;DR

Jiffy is a novel lock-free skip list data structure that supports atomic batch updates and consistent snapshots, optimizing performance for various workloads through adaptive revision sizing and efficient concurrency control.

Contribution

It introduces Jiffy, the first lock-free, linearizable ordered key-value index with batch updates and snapshots, utilizing multiversioned skip list and adaptive revision sizes.

Findings

Achieves performance comparable or better than state-of-the-art lock-free indices.

Supports large batch updates up to 7.4x more efficiently than lock-based rivals.

Provides adaptable performance for different workload contention levels.

Abstract

In this paper we introduce Jiffy, the first lock-free, linearizable ordered key-value index that offers both (1) batch updates, which are put and remove operations that are executed atomically, and (2) consistent snapshots used by, e.g., range scan operations. Jiffy is built as a multiversioned lock-free skip list and relies on CPU's Time Stamp Counter register to generate version numbers at minimal cost. For faster skip list traversals and better utilization of the CPU caches, key-value entries are grouped into immutable objects called revisions. Moreover, by changing the size of revisions and thus modifying the synchronization granularity, our index can adapt to varying contentions levels (smaller revisions are more suited for write-heavy workloads whereas large revisions benefit read-dominated workloads, especially when they feature many range scan operations). Structure modifications to the index, which result in changing the size of revisions, happen through (lock-free) skip list node split and merge operations that are carefully coordinated with the update operations. Despite rich semantics, Jiffy offers highly scalable performance, which is comparable or exceeds the performance of the state-of-the-art lock-free ordered indices that feature linearizable range scan operations. Compared to its (lock-based) rivals that also support batch updates, Jiffy can execute large batch updates up to 7.4x more efficiently.