Despite extensive in-house testing, bugs often escape to deployed software. Whenever a failure occurs in production software, it is desirable to collect as much execution information as possible so as to help developers reproduce, diagnose and fix the bug. To reconcile the tension between trace capability, runtime overhead, and trace scale, we propose continuous tail tracing for production use. Instead of capturing only crash stacks, we produce the complete sequence of function calls and returns. Importantly, to avoid the overwhelming stress to I/O, storage, and network transfer caused by the tremendous amount of trace data, we only retain the final segment of trace. To accomplish it, we design a novel trace decoder to support precise tail trace decoding, and an effective path-based instrumentation-site selection algorithm to reduce overhead. We implemented our approach as a tool called TailTracer on top of LLVM, and conducted the evaluations over the SPEC CPU 2017 benchmark suite, the open-source database system, and real-world bugs. The experimental results validate that TailTracer achieves low-overhead tail tracing, while providing more informative trace data than the baseline.

Database Management Systems (DBMSs) are fundamental to numerous enterprise applications. Due to the significance of DBMSs, various testing techniques have been proposed to detect DBMS bugs. However, to trigger deep bugs, most of the existing techniques focus on generating lengthy and complex queries which burdens developers with the difficult of debugging. Therefore, SQL query simplification, which aims to reduce lengthy SQL queries without compromising their ability to detect bugs, is highly demanded. To bridge this gap, we introduce SQLess, an innovative approach that employs a dialect-agnostic method for efficient and semantically correct SQL query simplification tailored for various DBMSs. Unlike previous works that have to depend on DBMS-specific grammar, SQLess utilizes an adaptive parser, which leverages error recovery and grammar expansion to support DBMS dialects. Moreover, SQLess performs a semantics-sensitive SQL query trimming, which leverages alias and dependency analysis to simplify SQL queries with preserving bug-triggering capability. We evaluate SQLess using two datasets from the state-of-theart database bug detection studies, encompassing six widely-used DBMSs and over 32,000 complex SQL queries. The results demonstrate SQLess’s superior performance: it achieves an average simplification rate of 72.45%, which significantly outperforms the stateof-the-art approaches by 84.91%.