Implements the Ribbon filter algorithm, a space-efficient approximate membership query data structure that outperforms Bloom filters in many scenarios. The implementation is self-contained, uses template metaprogramming for compile-time optimization, and handles both 32-bit and 64-bit configurations. It is a non-obvious, well-crafted algorithm that can be extracted and used in any project requiring high-performance set membership testing.

A drop-in replacement for std::vector optimized for small sizes. It stores a fixed number of elements inline (configurable via template parameter) and only dynamically allocates when the size exceeds that threshold. The implementation is thread-safe for reads, provides RAII semantics, and avoids heap allocations for common small vectors. Completely standalone, it can be reused in any C++ project to reduce memory allocation overhead.

A simple and efficient arena allocator that allocates memory in large blocks and provides fast, O(1) allocations without deallocation. It supports alignment, custom allocator hooks, and integration with memory tracing. The code is clean, well-documented, and used extensively throughout RocksDB. It can be easily extracted and reused in other performance-sensitive applications.

A bounded multi-producer, multi-consumer work queue template that supports blocking push/pop with timeout and peek. It uses std::mutex and std::condition_variable for synchronization and can be instantiated with custom lock types. The implementation is minimal, well-tested, and can be reused in any project needing a thread-safe task queue.