CockroachDB is a cloud-native distributed SQL database built on a transactional, strongly-consistent key-value store (Pebble). It provides horizontal scalability, survivability against disk/machine/rack/datacenter failures with minimal latency disruption, strongly-consistent ACID transactions, and a PostgreSQL-compatible SQL API. The architecture is a monolithic Go application with a clear separation between the SQL layer (parser, optimizer, distributed execution engine) and the KV layer (Raft-based replication, Pebble storage). Key innovations include a Cascades-style cost-based optimizer with memoization, a vectorized columnar execution engine (colexec), online declarative schema changes, distributed backup/restore with incremental support, change data capture with multiple sink formats, and multi-region/multi-tenant capabilities with geo-partitioning. The codebase demonstrates exceptional engineering craftsmanship throughout - the Raft implementation, distributed SQL planner, admission control system, and time-series storage are all genuinely reusable components that showcase non-obvious solutions to hard distributed systems problems. Active development with recent commits, comprehensive CI/CD, and regular releases.