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Highest Response Ratio Next Scheduling

Highest Response Ratio Next Scheduling chooses jobs using priority, completion-time, or resource-availability rules.

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Quick Facts

Compact metadata for implementation and discovery.

Category: Scheduling
Difficulty: Intermediate
Family: Scheduling
Tier: Core
Status: Verified
Review: Source Checked
Sources: 1
Formulas: 1
Relationships: 1
Code example: Ready
Visualization: Ready
Aliases: HRRN

Overview

Highest Response Ratio Next Scheduling is a scheduling method that selects or admits work using a concrete priority, fairness, deadline, or capacity rule. It helps expose the policy tradeoff behind queue order, fairness, deadlines, or resource use.

Core Concepts

priority ruleresource allocationqueue disciplinetask order

Quick facts

Complexity

Runtime and memory behavior at a glance.

Best

O(n)

Average

O(n log n)

Worst

O(n^2)

Space

O(n)

When to Use

Use Highest Response Ratio Next Scheduling when queue order, resource assignment, or deadline policy must be explicit.
Use it when comparing fairness, latency, throughput, or utilization policies matters.

When Not to Use

Avoid when the policy would hide starvation, unfairness, or deadline misses.
Avoid when task durations or priorities are too uncertain for the rule to be meaningful.

What It Does

Ranks ready work with a scheduling rule
Updates waiting time, deadlines, or capacity
Returns an order, assignment, or admission decision

Use Cases

CPU scheduling
Network queue management
Workflow and batch processing

Inputs

Jobs or requests
Timing constraints
Resource limits

Outputs

Execution order
Resource assignment
Timing decision

Key Formulas (1)

Response ratio

ratio = (waiting_time + service_time) / service_time

ratio = (waiting_time + service_time) / service_time

Ranks ready jobs by balancing waiting time against expected service time.

Pseudocode

1.Collect ready jobs, queues, or tasks
2.Compute the method's priority, fairness, or capacity score
3.Select the next job or resource assignment
4.Update waiting time, capacity, or completion state
5.Repeat until all work is scheduled or admitted

Canonical Example

Input: jobs = [{id:A, time:3}, {id:B, time:1}], resource = one worker
Output: ordered or assigned jobs according to the scheduling rule
Explanation: Highest Response Ratio Next Scheduling computes the priority or capacity rule and chooses the next job from the ready set.

Implementation Notes

Make tie-breaking deterministic and visible in tests.
Track waiting time, service time, and resource state separately.
State whether the policy is preemptive and what fairness, latency, or deadline objective it optimizes.

Common Pitfalls

Forgetting tie-breaking rules makes schedules unstable across runs.
Ignoring starvation and fairness edge cases can make good averages hide bad tail behavior.
Ignoring preemption cost, release times, or starvation can make a schedule look correct only in toy cases.

Interactive Mechanism Walkthrough

Graph Frontier & Edge Relaxation

Show queued jobs moving onto processors, links, or time slots as the scheduling rule changes priorities.

Step 1 of 5: Collect ready jobs, queues, or tasks

scheduling

Notes

Highest Response Ratio Next Scheduling operates in O(n log n) time and O(n) space within the Scheduling family. Key governing relation: ratio = (waiting_time + service_time) / service_time. Often compared with Round Robin Scheduling and Priority Scheduling.

Sources (1)

What each reference supports for this entry.

Operating System Concepts

Book

Operating-systems reference for HRRN non-preemptive CPU scheduling, response-ratio ranking, and starvation mitigation.

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Alternative toRound Robin Scheduling

Scheduling · Foundation

HRRN is a non-preemptive response-ratio policy, while round robin is a preemptive time-slicing policy.

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