All 7 Redis as a Message Queue questions
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What options does Redis offer for implementing a message queue, and how do they differ from each other? How do you build a simple work queue using a Redis list where multiple workers pull tasks to process? What are the limitations of using a plain Redis list as a message queue, and when should you consider Redis Streams instead? How do you monitor the length and health of a Redis based queue to ensure workers are keeping up with incoming tasks? How would you implement a delayed task queue in Redis, where a task should only become available for processing after a specific future time? What patterns help ensure exactly once or at least once processing semantics when using Redis as a message queue for critical tasks?
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How do you implement a priority queue pattern using Redis, where certain tasks should be processed before others?

Intermediate

Answer

You can use a sorted set instead of a plain list, storing each task with a score representing its priority, and have workers retrieve the highest or lowest priority task using ZPOPMIN or ZPOPMAX, ensuring that more urgent tasks are always processed ahead of lower priority ones regardless of the order they were originally added.
ZADD priority_queue 1 'urgent_task'
ZADD priority_queue 5 'normal_task'
ZPOPMIN priority_queue
Real-world example A customer support ticketing system uses a sorted set based priority queue, ensuring tickets marked as urgent are always processed by available agents before lower priority tickets, regardless of when each ticket was originally submitted.

Common follow-ups: How do you handle two tasks that happen to have the exact same priority score?;Is ZPOPMIN an atomic operation safe for multiple concurrent workers?

Sets & Sorted Sets in Redis;Data Types
All 7 Redis as a Message Queue questions