A Contention-Friendly, Non-Blocking Skip List

This paper presents a new non-blocking skip list algorithm. The algorithm alleviates contention by localizing synchronization at the least contended part of the structure without altering consistency of the implemented abstraction. The key idea lies in decoupling a modification to the structure into two stages: an eager abstract modification that returns quickly and whose update affects only the bottom of the structure, and a lazy selective adaptation updating potentially the entire structure but executed continuously in the background. As non-blocking skip lists are becoming appealing alternatives to latch-based trees in modern main-memory databases, we integrated it into a main-memory database benchmark, SPECjbb. On SPECjbb as well as on micro-benchmarks, we compared the performance of our new non-blocking skip list against the performance of the JDK non-blocking skip list. Results indicate that our implementation is up to 2:5 faster than the JDK skip list