How to implement redis delay queue

The implementation of Redis delay queue uses an ordered set, stores tasks as scores (timestamps), regularly retrieves expired tasks, deletes and executes them. The steps are as follows: Create an ordered collection delayed_queue and store the task as a fraction (timestamp). Retrieve expired tasks with scores between 0 and the current timestamp. Delete expired tasks. Perform expired tasks.

Redis delay queue implementation

Redis is a high-performance in-memory database that provides a variety of data structures including lists, collections, and hash tables. We can use these data structures to implement a delay queue.

Implementation principle

The implementation idea of ​​Redis delay queue is:

1. Create an ordered set delayed_queue where each element is a key-value pair with a score (timestamp).
2. Put the task to be delayed into delayed_queue and use the task execution time as a score.
3. Regularly use the zrangebyscore command to retrieve expired tasks and delete them from the queue.
4. Perform expired tasks.

Detailed steps

1. Create an ordered collection:

    <code class="redis">ZADD delayed_queue 1640995200 task1 ZADD delayed_queue 1640995600 task2</code>

2. Retrieve expired tasks:

    <code class="redis">ZRANGEBYSCORE delayed_queue 0 1640995200 LIMIT 0 1</code>

3. Delete expired tasks:

    <code class="redis">ZREM delayed_queue task1</code>

4. Perform expired tasks:
   The logic for performing tasks depends on the specific scenario, and can be sending emails, triggering events, or performing other actions.

advantage

• Efficient: Redis's underlying layer uses high-performance hash tables that can efficiently perform ordered collection operations.
• Reliable: Redis supports data persistence, and data will not be lost even if there is a failure.
• Scalable: Redis can be scaled horizontally to handle high loads.

limitation

• Redis has no hard limit on the length of a list or ordered set, but excessive queues may affect performance.
• Redis does not support priorities for tasks.

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