TiDB is a production-grade, open-source distributed SQL database with MySQL compatibility, horizontal scalability, strong consistency (ACID), and HTAP capabilities via TiKV (row store) and TiFlash (columnar store). The architecture separates compute (TiDB Server) from storage (TiKV/TiFlash) with PD for cluster management. Key entry points: cmd/tidb-server (SQL layer), lightning/cmd/tidb-lightning (TB-scale import), br/cmd/br (backup/restore), dumpling/cmd/dumpling (export). The codebase demonstrates exceptional craftsmanship with a modular design: the parser (pkg/parser) is a standalone MySQL-compatible SQL parser used by external projects; pkg/objstore provides a unified storage abstraction (S3/GCS/Azure/local/HDFS) with compression/encryption; pkg/dxf/framework implements a distributed execution framework with scheduler/task-executor/planner; pkg/timer provides distributed cron/interval scheduling with persistence; pkg/extension enables plugin-based authentication/session-hooks/custom-functions; pkg/util/chunk/arena/zeropool/mvmap/intset/bitmap provide high-performance columnar processing and memory management; pkg/expression uses code generation for vectorized SIMD evaluation; pkg/planner implements a Cascades-based cost-based optimizer with plan caching; pkg/ddl executes online schema changes via job-based distributed backfill with schema versioning; pkg/statistics maintains histograms/CMS/FM-sketch with auto-analyze priority queues. The repo includes comprehensive testing (unit, integration, realtikv, chaos) and modern Go practices (generics, interfaces, DI).
BuntDB is a low-level, in-memory, key/value store library in Go. It supports custom indexing (B-tree and R-tree), geospatial queries, JSON indexing, TTL expiration, and ACID transactions with multiple readers / single writer. Persistence is via an append-only file (AOF) with automatic background shrinking. The library is designed for high performance and embeddability, and is used by projects requiring a fast, reliable embedded database. The codebase is a single package with a well-structured API, comprehensive tests, and minimal dependencies.
SpacetimeDB is a real-time database system that enables developers to upload application logic directly into the database as modules, eliminating the need for traditional backend servers. Clients connect directly to the database using language-specific SDKs (Rust, C#, TypeScript, C++, Unreal) and receive real-time updates when data changes. The system features a Rust-based core server, WebSocket-based synchronization, ACID transactions, and a code generation system that creates language bindings from module definitions. Notable features include schema evolution capabilities, scheduled procedures, and row-level security. The entire backend of MMORPG BitCraft Online runs as a single SpacetimeDB module, demonstrating its capacity for complex, high-performance applications.
Sled is an embedded key-value store written in Rust that provides ACID transactions, crash safety, and high concurrency. It uses a lock-free architecture based on a lock-free pagecache, lock-free log, and lock-free B+ tree with epoch-based memory reclamation. The database supports multiple keyspaces, watch prefixes, merge operators, and a crash-safe monotonic ID generator. Currently in active development with a major rewrite underway (komora project), it is alpha software with known instability and frequent breaking changes, but demonstrates advanced concurrent data structure techniques.