How to set the redis expiration policy

There are two types of Redis expiration strategies: periodic deletion and lazy deletion. Regularly delete actively scan the database in the background, immediately delete expired key-value pairs, saving memory space, but may affect performance. Lazy deletion is only deleted when the client accesses expired key-value pairs, which are low in performance overhead, but expired key-value pairs may continue to take up memory space. Applications should choose policies based on requirements, if required to delete immediately or performance is preferred. Optimization measures include the use of short TTL values, the distribution of data by Redis Cluster, and monitoring memory usage.

Redis Expiration Policy Settings

1. Overview

The Redis expiration policy defines how Redis handles key-value pairs when they expire. There are two main strategies: "Registration" and "Late Delete".

2. Delete regularly

• Use the expires command to set the time of survival (TTL) of key-value pairs.
• Redis scans the database regularly in the background to delete expired key-value pairs.
• Advantages: Ensure that all expired key-value pairs are deleted in time and save memory space.
• Disadvantages: The scanning process can affect Redis performance, especially when the database is large.

3. Lazy deletion

• Redis will delete the expired key-value pair only when the client tries to access it.
• This policy does not actively scan the database and therefore does not affect Redis performance.
• Advantages: Low performance overhead.
• Disadvantages: Expired key-value pairs may continue to occupy memory space for a period of time.

4. Setting method

4.1 Regularly deleted

 <code>EXPIRE mykey 60 # 设置mykey 的TTL 为60 秒</code>

4.2 Lazy deletion

Redis uses a lazy delete policy by default. You can use the following command to disable lazy deletion and enable periodic deletion:

 <code>config set lazyfree-lazy-eviction no</code>

5. Select a policy

Which strategy to choose depends on the specific needs of the application:

• If you need to delete expired key-value pairs immediately, select Delete periodically.
• If performance is a priority, choose lazy deletion.

6. Optimization

• Use short TTL values ​​to reduce the number of expired key-value pairs.
• Consider using Redis Cluster, which can distribute data across multiple nodes, reducing the scanning burden of a single node.
• Monitor Redis memory usage regularly and adjust TTL values ​​and deletion policies if needed.

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