Detailed explanation of delayed task scheduling in Redis

With the continuous development of Internet and cloud computing technology, delayed task scheduling is becoming more and more common in daily development work, such as sending emails regularly, backing up databases regularly, and so on. As the complexity and magnitude of tasks continue to increase, many traditional scheduling methods can no longer meet the needs, so an efficient and reliable delayed task scheduling system is needed. As a high-performance in-memory database, Redis has naturally become a powerful tool for implementing delayed task scheduling.

This article will introduce in detail the steps and related technical details of using Redis to implement delayed task scheduling.

1. Redis data structure

Before understanding Redis’ implementation of delayed task scheduling, you need to first understand its basic data structure. Redis supports five basic data types, namely string, list, hash, set, and zset. Among them, zset (ordered set) is the core data structure for implementing delayed task scheduling.

zset is an ordered set in Redis. Each member of it has a score value that can be used for sorting. In zset, each member has a unique key and corresponding score. zset provides the same set operations as set, and also supports obtaining members according to the score range or ranking.

2. Implement delayed task scheduling

The core idea of ​​implementing delayed task scheduling in Redis is to insert the tasks to be executed into zset and set the execution time of the task as the score. The server side of Redis provides multiple commands for operating ordered collections. These commands can easily implement delayed task scheduling.

1. Add tasks

Use the zadd command to add tasks to zset and specify the execution time of the task as the score. If the task already exists, its score value will be updated.

For example: zadd delay_queue 1630509327 "task1"

When the delay time reaches 1630509327, Redis will automatically move the "task1" task out of the delay_queue ordered set and place it elsewhere for processing.

2. Get the task

Use the zrange command to get the members in zset whose score is within a certain range.

For example: zrange delay_queue 0 0

This command will return the member with the smallest score in the delay_queue ordered set, which is the earliest task.

3. Delete task

Use the zrem command to delete a member of the zset.

For example: zrem delay_queue "task1"

This command will remove the "task1" task from the delay_queue ordered set.

4. Listening tasks

Use the blpop command to implement the blocking queue function of Redis. This command will block until the task is dequeued.

For example: blpop delay_queue 0

This command will block until a member of the delay_queue ordered set is dequeued.

3. Complete implementation of delayed task scheduling

Now, let’s look at a complete implementation process of Redis delayed task scheduling.

1. Initialize Redis connection

In Python, we can use the redis-py library to connect to Redis and operate Redis.

import redis
r = redis.Redis(host='localhost', port=6379, db=0)

2. Add task

We can add tasks to zset in the following ways:

r.zadd('delay_queue', {'task1': 1630509327})

Represents adding task "task1" to "delay_queue" In the sequence set, the delay time is 1630509327.

3. Get the task

We can get the earliest task in the following way:

task = r.zrange('delay_queue', 0, 0, withscores=True)

represents getting the smallest score in the "delay_queue" ordered set member, that is, the earliest task, and returns the key and score values ​​of the task.

4. Perform tasks

We can perform corresponding actions after the task expires:

def do_task(task_key):
    # do your task here
    print('do task', task_key)

# 监听任务
while True:
    task = r.zrange('delay_queue', 0, 0, withscores=True)
    if task:
        task_key, score = task[0]
        # 如果任务时间到了，则执行任务
        if score <= time.time():
            r.zrem('delay_queue', task_key) # 删除已完成的任务
            do_task(task_key) # 执行任务
    time.sleep(0.1) # 避免CPU占用率过高

In the above code, we use a while loop to continuously Remove the earliest task from zset. If the task time has expired, perform the corresponding action and delete the task from zset.

4. Summary

This article introduces how to use Redis to implement delayed task scheduling. Through the ordered set data structure of zset and multiple commands provided by Redis, you can easily implement an efficient and reliable Delayed task scheduling system. Of course, this is not the only implementation method. Different methods may be used in different scenarios and need to be adjusted according to actual business needs.

Finally, it is worth mentioning that when the task volume is large, using Redis to implement delayed task scheduling may put a great burden on Redis, leading to a decrease in Redis performance. Therefore, in actual applications, it is necessary to decide whether to use Redis to implement delayed task scheduling based on factors such as specific business requirements and system load.

The above is the detailed content of Detailed explanation of delayed task scheduling in Redis. For more information, please follow other related articles on the PHP Chinese website!