Tensions in Practice: Arrival order in tension with short-job responsiveness¶
Work scheduling · one service slot
Three jobs are ready for one worker: a long job arrived first, followed by two short jobs. Keeping arrival order makes the short jobs wait for the long one. Serving short jobs first gets them out sooner but moves the first arrival to the back. If short jobs keep arriving, that displacement can continue indefinitely.
Honor arrival order
Do not let later work repeatedly pass an earlier waiting job.
Finish short work sooner
Avoid making many small jobs wait behind one long job.
Why these aims pull against each other
The same service capacity can distribute waiting differently. A rule that improves short-job response can transfer the delay to long jobs.
Choose an arrangement to see what changes and what remains difficult.
Qualitative paths and conditions, not measured costs, timings or performance guarantees.
What this choice protects
What it costs
When it fits
Compare the arrangements
Arrival order
Serve the three waiting jobs in the order they arrived.
- What it protects
- The earlier job is not overtaken simply because it is long.
- What it costs
- Both short jobs must wait for the long job to finish.
- When it fits
- Arrival-order predictability matters, lengths are unknown, or repeated overtaking would be unacceptable.
Illustration note: The finite three-job illustration is editorial. It assumes no preemption and does not estimate waiting times.
Short work first
Serve the two known short jobs before the long job.
- What it protects
- The short jobs finish without waiting for the long job’s full service.
- What it costs
- The long job is overtaken; an ongoing stream of shorter jobs can starve it without an additional rule.
- When it fits
- Service lengths are known or reliably estimated and the application can tolerate or separately bound overtaking.
Illustration note: The source’s mean-wait advantage is used only for the stated finite, already-ready, known-length setting. No universal optimum or starvation cure is implied.
What this illustration does—and does not—establish
Queueing: Queueing Discipline Has Fairness and Psychological Consequences supplies the discipline conflict. The three invented jobs make the changed service order inspectable.
- The diagrams show order, not measured durations or equal work per box.
- The example holds capacity and the ready jobs fixed; it does not show preemption, priorities, or deadlines.
- An infinite supply of shorter jobs is a separate extension illustrating the starvation risk, not a property of the finite three-job queue.
Source entries
Queueing
Queueing: Queueing Discipline Has Fairness and Psychological Consequences supplies the conflict examined here.
Queueing Discipline Has Fairness and Psychological Consequences
FIFO is "fair" in an arrival-order sense but may be unfair by service-need (a long service blocks many short ones); SJF (Shortest Job First) minimizes mean wait but starves long jobs;