Priority queue pattern in Redis

Introduction

A priority queue helps you manage tasks or items where some are more important than others. It lets you always get the highest priority item first.

You want to process urgent customer support tickets before others.

You need to run jobs where some have deadlines sooner than others.

You want to manage tasks in a game where some actions have higher priority.

You want to schedule messages to be sent based on importance.

You want to handle events where some must happen before others.

Syntax

Redis

ZADD key [NX|XX] [CH] [INCR] score member [score member ...]
ZPOPMIN key [count]
ZRANGE key start stop [WITHSCORES]

Redis uses sorted sets (ZSET) to implement priority queues.

Scores represent priority: lower score means higher priority.

Examples

Adds tasks with different priorities (1 is highest priority).

Redis

ZADD tasks 1 "task1" 5 "task2" 3 "task3"

Removes and returns the task with the highest priority (lowest score).

Redis

ZPOPMIN tasks

Shows the highest priority task without removing it.

Redis

ZRANGE tasks 0 0 WITHSCORES

Sample Program

This example adds three tasks with different priorities. Then it shows the highest priority task, removes it, and finally shows the remaining tasks.

Redis

ZADD priority_queue 10 "low_priority_task" 1 "high_priority_task" 5 "medium_priority_task"
ZRANGE priority_queue 0 0 WITHSCORES
ZPOPMIN priority_queue
ZRANGE priority_queue 0 -1 WITHSCORES

Important Notes

Adding items (ZADD) and removing the highest priority item (ZPOPMIN) both run fast, usually in O(log n) time.

Use ZPOPMIN to get and remove the highest priority item atomically.

Common mistake: Using higher scores as higher priority. In Redis sorted sets, lower scores mean higher priority.

Use this pattern when you want to process items in order of importance or urgency.

Summary

Priority queues let you handle items by importance using Redis sorted sets.

Lower scores mean higher priority in Redis.

Use ZADD to add items and ZPOPMIN to get and remove the highest priority item.