Eviction policies overview in Redis

Introduction

Eviction policies help Redis decide which data to remove when it runs out of memory. This keeps Redis fast and prevents crashes.

When your Redis server has limited memory and you want to keep it running smoothly.

When you want to control which data stays in Redis and which data gets removed automatically.

When you use Redis as a cache and want old or less important data to be removed first.

When you want to avoid errors caused by Redis running out of memory.

When you want to balance memory use and data freshness in your application.

Syntax

Redis

CONFIG SET maxmemory-policy <policy_name>

You set the eviction policy using the CONFIG SET command.

The <policy_name> is the name of the eviction policy you want to use.

Examples

This policy means Redis will not remove any data and will return errors when memory is full.

Redis

CONFIG SET maxmemory-policy noeviction

This policy removes the least recently used keys from all keys when memory is full.

Redis

CONFIG SET maxmemory-policy allkeys-lru

This policy removes the least recently used keys only among keys with an expiration time set.

Redis

CONFIG SET maxmemory-policy volatile-lru

This policy removes random keys from all keys when memory is full.

Redis

CONFIG SET maxmemory-policy allkeys-random

Sample Program

This sets Redis to use 100 megabytes of memory and to remove the least recently used keys from all keys when memory is full.

Redis

CONFIG SET maxmemory 100mb
CONFIG SET maxmemory-policy allkeys-lru

Important Notes

Eviction policies only work if you set a memory limit with maxmemory.

Choosing the right policy depends on your use case, like caching or persistent storage.

Common policies include noeviction, allkeys-lru, volatile-lru, allkeys-random, and volatile-random.

Summary

Eviction policies control how Redis frees memory when it is full.

You set eviction policies with CONFIG SET maxmemory-policy.

Pick a policy that fits your app's needs to keep Redis fast and stable.