publications

2024

1. IONIA: High-Performance Replication for Modern Disk-based KV Stores

   Yi Xu*, Henry Zhu*, Prashant Pandey, and 4 more authors

   In 22nd USENIX Conference on File and Storage Technologies (FAST 24) , 2024

   Abs

   We introduce IONIA, a novel replication protocol tailored for modern SSD-based write-optimized key-value (WO-KV) stores. Unlike existing replication approaches, IONIA carefully exploits the unique characteristics of SSD-based WO-KV stores. First, it exploits their interface characteristics to defer parallel execution to the background, enabling high-throughput yet one round trip (RTT) writes. IONIA also exploits SSD-based KV-stores’ performance characteristics to scalably read at any replica without enforcing writes to all replicas, thus providing scalability without compromising write availability; further, it does so while completing most reads in 1RTT. IONIA is the first protocol to achieve these properties, and it does so through its storage-aware design. We evaluate IONIA extensively to show that it achieves the above properties under a variety of workloads.

2022

1. Towards Practical Application-level Support for Privilege Separation

   Nik Sultana, Henry Zhu, Ke Zhong, and 9 more authors

   In 2022 Annual Computer Security Applications Conference (ACSAC) , 2022

   Abs

   Privilege separation (privsep) is an effective technique for improving software’s security through the compartmentalization of code, data, and dependencies in which we have limited trust. Applying privsep involves separating software components from each other and assigning them different privileges. This often involves ad hoc, laborious and error-prone restructuring of software into concurrent processes. This effort hinders the application of privsep

2020

1. Debugging strongly-compartmentalized distributed systems

   Henry Zhu, Nik Sultana, and Boon Thau Loo

   In 2020 IEEE International Parallel and Distributed Processing Symposium Workshops (IPDPSW) , 2020

   Abs

   Splitting software into distributed compartments is an important software security technique that limits the effect of vulnerabilities. Unfortunately the resulting systems are difficult to analyze or debug interactively when compared to the original. Not only are compartments distributed and executed in parallel, but they may also be strongly isolated by being sandboxed or run in minimal environments that lack debugging facilities.This paper is the first to study practical debugging techniques for strongly-isolated distributed compartments. We adapt ideas from other remote or distributed debugging settings to this domain, and implement and describe two radically different approaches to this problem. We evaluate these approaches both qualitatively and quantitatively, and using both toy examples and real-world open-source software. Our main finding is that out of the two approaches, using GDB remote stubs presents a good balance of performance, flexibility and usability, and we characterize this more precisely in our evaluation

2019

1. Trace-based Behaviour Analysis of Network Servers

   Nik Sultana, Achala Rao, Zihao Jin, and 4 more authors

   In 2019 15th International Conference on Network and Service Management (CNSM) , 2019

   Abs

   Analysing software and networks can be done using established tools, such as debuggers and packet analysers, but using established tools to analyse network software is difficult and impractical because of the sheer detail the tools present and the performance overheads they typically impose. This makes it difficult to precisely diagnose performance anomalies in network software to identify their causes (is it a DoS attack or a bug?) and determine what needs to be fixed.We present Flowdar: a practical tool for analysing software traces to produce intuitive summaries of network software behaviour by abstracting unimportant details and demultiplexing traces into different sessions’ subtraces. Flowdar can use existing state-of-the-art tracing tools for lower overhead during trace gathering for offline analysis. Using Flowdar we can drill down when diagnosing performance anomalies without getting overwhelmed in detail or burdening the system being observed. We show that Flowdar can be applied to existing real-world software and can digest complex behaviour into an intuitive visualisation.

2018

1. Making Break-ups Less Painful: Source-level Support for Transforming Legacy Software into a Network of Tasks

   Nik Sultana, Achala Rao, Zihao Jin, and 4 more authors

   In Proceedings of the 2018 Workshop on Forming an Ecosystem Around Software Transformation , 2018

   Abs

   "Breaking up" software into a dataflow network of tasks can improve availability and performance by exploiting the flexibility of the resulting graph, more granular resource use, hardware concurrency and modern interconnects. Decomposing legacy systems in this manner is difficult and ad hoc however, raising such challenges as weaker consistency and potential data races. Thus it is difficult to build on battle-tested legacy systems. We propose a paradigm and supporting tools for developers to recognize task-level modularity opportunities in software. We use the Apache web server as an example of legacy software to test our ideas. This is a stepping stone towards realizing a vision where automated decision-support tools assist in the decomposition of systems to improve the reuse of components, meet performance targets or exploit new hardware devices and topologies.