Title: Demystifying and Checking Silent Semantic Violations in Large Distributed Systems
Speaker: Chang Lou (Johns Hopkins University)
Time: 11:00 am, July 06 (Wednesday), 2022
Location: N/A
Online link: provided upon request or see the seminar email.


Distributed systems today offer rich features with numerous semantics that users depend on. Bugs can cause a system to silently violate its semantics without apparent anomalies. Such silent violations cause prolonged damage and are difficult to address. Yet, this problem is under-investigated. In this paper, we first study 109 real-world silent semantic failures from nine widely-used distributed systems to shed some light on this difficult problem. Our study reveals more than a dozen informative findings. For example, it shows that surprisingly the majority of the studied failures were violating semantics that existed since the system’s first stable release. Guided by insights from our study, we design Oathkeeper, a tool that automatically infers semantic rules from past failures and enforces the rules at runtime to detect new failures. Evaluation shows that the inferred rules detect newer violations, and Oathkeeper only incurs 1.27% overhead.


Chang Lou is a Ph.D. candidate in the Department of Computer Science at Johns Hopkins University, advised by Prof. Ryan (Peng) Huang. His main research interests are improving system availability and reliability. Specifically, his past work focuses on enhancing cloud systems’ observability by understanding and detecting complex failures beyond the fail-stop model. His research received USENIX NSDI Best Paper Award (2020). He received his B.S. degree in Computer Science from Shanghai Jiao Tong University in 2016.