Que is a high-performance job queue that improves the reliability of your
application by protecting your jobs with the same ACID guarantees as the rest of
your data.

Que is a queue for Ruby and PostgreSQL that manages jobs using advisory locks,
which gives it several advantages over other RDBMS-backed queues:
- Concurrency - Workers don't block each other when trying to lock jobs, as
  often occurs with "SELECT FOR UPDATE"-style locking. This allows for very high
  throughput with a large number of workers.
- Efficiency - Locks are held in memory, so locking a job doesn't incur a disk
  write. These first two points are what limit performance with other queues.
  Under heavy load, Que's bottleneck is CPU, not I/O.
- Safety - If a Ruby process dies, the jobs it's working won't be lost, or left
  in a locked or ambiguous state - they immediately become available for any
  other worker to pick up.

WWW: https://github.com/que-rb/que