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How would you track and expose the progress of a long-running background job to the client that requested it? What are the trade-offs of using an in-memory job queue (like a simple array-based queue) versus a persistent, Redis-backed queue? What is a 'stalled' job in BullMQ, and what causes it? What is a dead-letter queue (DLQ), and how should a Node.js job-processing system use one? What is the difference between a message queue (like RabbitMQ) and a job queue (like BullMQ), and when would you choose one over the other? How do you implement graceful shutdown for a Node.js background worker process to avoid losing or corrupting in-progress jobs? What is job de-duplication in a queue system, and how would you prevent the same logical job from being enqueued multiple times? How do you implement rate-limited job processing so a Node.js worker doesn't exceed a downstream third-party API's request limits?
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How do you implement job prioritization in a Node.js queue system, and when is it necessary?

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Answer

Job prioritization lets certain jobs jump ahead of others in the processing order -- necessary when different job types or tenants have different urgency (a paying customer's export request versus a routine nightly cleanup task) and a strict first-in-first-out queue would make urgent work wait behind a backlog of lower-priority jobs. Most queue libraries support this natively via a numeric priority value assigned when a job is added, with workers pulling higher-priority jobs first.
// BullMQ: lower numbers = higher priority
await queue.add('export', premiumUserData, { priority: 1 });
await queue.add('export', freeUserData, { priority: 10 });

// Workers automatically process priority 1 jobs before priority 10 jobs
// when both are waiting in the queue
Real-world example A SaaS platform assigns a higher priority to report-generation jobs from enterprise customers on premium plans, so their exports complete quickly even during periods when the queue has a large backlog of lower-priority free-tier requests waiting behind them.

Common follow-ups: What's the risk of starvation for low-priority jobs if high-priority jobs keep arriving continuously?;How would you combine priority with a separate fairness mechanism to prevent that starvation?

Performance Optimization & Profiling;Advanced Node.js
All 15 Background Jobs & Queues questions