Glossary · System coordination, integration and orchestration
Queue discipline
Also known as: Queuing discipline, Service discipline
German: Warteschlangendisziplin
In queueing theory and system design, the queue discipline is the rule that determines the order in which waiting items, such as jobs, messages or requests, are taken from a queue for service, for example first in, first out (FIFO), last in, first out (LIFO) or priority-based.
- System integration
In one sentence
The queue discipline sets the order in which waiting jobs, messages or requests leave a queue, e.g. FIFO, LIFO or priority-based.
Example
Pallets on an accumulating conveyor follow FIFO by design, while alarm messages in the controller's message queue are served by priority.
How it applies
- Engineering: Physical queues (conveyors, buffers) often force FIFO. Software queues (messages, requests, tasks) can use any discipline. Choose the discipline deliberately and state it; the default of a library or broker may not match the requirement.
- Operation: Priority-based disciplines can starve low-priority items. Monitor waiting times, not only queue lengths.
- Traceability: For batch and lot traceability, a physical queue that does not keep FIFO (for example a mixing buffer) must be taken into account when assigning products to lots.
- Documentation: Specify the discipline in functional and interface specifications, and explain it in the operating instructions where operators can reorder items manually.
Queue discipline vs. priority rule
The queue discipline is the general ordering principle of a queue. A Priority rule is one specific criterion used in priority-based disciplines, such as earliest due date or Shortest processing time (SPT).