Rajeev Singh contributed to the Velox project by developing features that enhance query plan diagnosability and performance visibility. He introduced a header-only mode for query plan summaries in the IBM/velox repository, reducing verbosity for large plans through C++ code refactoring and query planning techniques. In facebookincubator/velox, he implemented adaptive per-function CPU sampling for expression evaluation, using algorithm design and benchmarking to minimize overhead while maintaining accurate performance tracking. Rajeev also stabilized flaky unit tests by refining sampling rate assertions, improving CI reliability. His work demonstrated depth in C++ development, performance optimization, and robust software testing within complex data processing systems.