How to Set Eviction Policy in Redis: Simple Guide

To set the eviction policy in Redis, use the maxmemory-policy configuration directive in the redis.conf file or via the CONFIG SET maxmemory-policy command. This policy controls how Redis removes keys when it reaches its memory limit, with options like noeviction, allkeys-lru, and volatile-lru.

Syntax

The eviction policy in Redis is set using the maxmemory-policy configuration. You can set it in the redis.conf file or dynamically with the CONFIG SET command.

• maxmemory-policy <policy>: Sets the eviction policy in the config file.
• CONFIG SET maxmemory-policy <policy>: Sets the eviction policy at runtime.

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

redis

maxmemory-policy noeviction

# Or at runtime:
CONFIG SET maxmemory-policy allkeys-lru

Example

This example shows how to set the eviction policy to allkeys-lru at runtime and verify it.

redis

127.0.0.1:6379> CONFIG SET maxmemory-policy allkeys-lru
OK
127.0.0.1:6379> CONFIG GET maxmemory-policy
1) "maxmemory-policy"
2) "allkeys-lru"

Output

OK
1) "maxmemory-policy"
2) "allkeys-lru"

Common Pitfalls

Common mistakes when setting eviction policy include:

• Not setting a maxmemory limit, so eviction never triggers.
• Choosing noeviction which causes writes to fail when memory is full.
• Confusing allkeys-* policies with volatile-* policies; the latter only evict keys with expiration set.

Always ensure maxmemory is configured to enable eviction.

redis

127.0.0.1:6379> CONFIG SET maxmemory-policy noeviction
OK
# If maxmemory is reached, writes will fail instead of evicting keys.

# Correct approach:
127.0.0.1:6379> CONFIG SET maxmemory 100mb
OK
127.0.0.1:6379> CONFIG SET maxmemory-policy allkeys-lru
OK

Output

OK
OK
OK

Quick Reference

Eviction Policy	Description
noeviction	No keys are evicted; writes fail when memory limit is reached.
allkeys-lru	Evicts least recently used keys from all keys.
volatile-lru	Evicts least recently used keys with expiration set.
allkeys-random	Evicts random keys from all keys.
volatile-random	Evicts random keys with expiration set.
volatile-ttl	Evicts keys with shortest time to live first.

Key Takeaways

Set the eviction policy using the maxmemory-policy directive in redis.conf or CONFIG SET.

Eviction only works if maxmemory is set to limit Redis memory usage.

Choose the right policy based on whether you want to evict all keys or only keys with expiration.

Avoid noeviction if you want Redis to free memory automatically.

Use CONFIG GET maxmemory-policy to verify the current eviction policy.