database systems

The .join() that should be a bug

3 months ago

Two classic database connection models exist: Redis's single-threaded model scales connections but forbids blocking, while Postgres's per-connection process model allows blocking but doesn't scale cheaply.
Kronotop splits connection handling from work processing: event loop threads (like Redis/Netty) manage thousands of connections without blocking, while virtual threads handle blocking I/O (e.g., FoundationDB calls, disk reads) in plain sequential code.
The system uses two executors—virtual threads for slow operations and Netty event loops for responses—ensuring connection threads stay free, with a strict hand-off rule for replies.
Kronotop connections hold client state, namespaces, authentication, and transactions, which are tied to the session and cleaned up on disconnection or reset, enabling easy reuse in client pools.
The .join() method in virtual threads allows blocking calls without wasting real threads, as the runtime parks and resumes them, eliminating waiting costs.