Betterment/delayed: a multi-threaded, SQL-driven ActiveJob backend used at Betterment to process millions of background jobs per day

Delayed is a multi-threaded, SQL-driven ActiveJob backend used at Betterment to process millions of background jobs per day. It supports postgres, mysql, and sqlite, and is designed to be: Reliable, with co-transactional job enqueues and guaranteed, at-least-once execution Scalable, with an optimized pickup query and concurrent job execution Resilient, with built-in retry mechanisms, exponential back-off, and failed job preservation Maintainable, with robust instrumentation, continuous monitoring, and priority-based alerting.