Shortest processing time is the dispatch rule that prioritizes jobs with the smallest operation time to reduce average queue and flow time - it is effective for throughput velocity but can starve long jobs.

What Is Shortest processing time?

• Definition: Scheduling policy that selects the lot with minimal estimated processing duration.
• Primary Objective: Minimize average waiting and completion time across queued jobs.
• Operational Character: Increases number of completed jobs per interval under stable conditions.
• Known Limitation: Long-duration lots may wait excessively without fairness controls.

Why Shortest processing time Matters

• Queue Reduction: Quickly clears many short operations, lowering average congestion.
• Cycle-Time Benefit: Often improves mean flow time in high-mix dispatch environments.
• Throughput Efficiency: Raises apparent movement rate at bottleneck resources.
• Tradeoff Awareness: Can worsen tail latency and due-date misses for long jobs.
• Policy Design Value: Useful component in hybrid multi-objective dispatch schemes.

How It Is Used in Practice

• Eligibility Filtering: Apply SPT within constraint-compliant candidate sets.
• Fairness Safeguards: Add aging penalties or max-wait constraints to prevent starvation.
• Scenario Tuning: Use simulation to determine where SPT improves or harms business metrics.

Shortest processing time is a strong queue-efficiency heuristic with known fairness risks - combining it with guardrails can preserve speed benefits while avoiding excessive delay for long operations.