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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 implement a priority queue pattern using Redis, where certain tasks should be processed before others? How do you monitor the length and health of a Redis based queue to ensure workers are keeping up with incoming tasks? 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 would you implement a delayed task queue in Redis, where a task should only become available for processing after a specific future time?

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Answer

You use a sorted set where the score represents the timestamp at which each task should become due, with a background process periodically checking for and moving any tasks whose due timestamp has already passed into an actual processing queue, effectively implementing scheduled, delayed task execution using Redis's native data structures.
ZADD delayed_tasks 1725800000 'send_reminder_email'
-- A background process periodically checks:
ZRANGEBYSCORE delayed_tasks 0 <current_timestamp>
Real-world example A reminder notification system schedules emails to be sent at a specific future time using a sorted set keyed by timestamp, with a background worker checking every few seconds for any reminders that have become due and moving them into the active processing queue.

Common follow-ups: How frequently should the background process check for due tasks?;How do you handle a task that needs to be cancelled before its scheduled time arrives?

Sets & Sorted Sets in Redis;Redis Performance Tuning & Benchmarking
All 7 Redis as a Message Queue questions