Question: How can you set the eviction policy in Redis?

Answer

Redis allows setting different types of eviction policies to control how data is removed from memory when it reaches its maximum limit. This is done by adjusting the maxmemory-policy configuration directive.

Here are the supported eviction methods:

1. noeviction: Returns an error when the memory limit is reached and the client tries to execute commands that could result in more memory being used.
2. allkeys-lru: Evicts the least recently used keys out of all keys.
3. volatile-lru: Evicts the least recently used keys among those set to have an expire set.
4. allkeys-random: Evicts random keys out of all keys.
5. volatile-random: Evicts random keys among those set to have an expire set.
6. volatile-ttl: Evicts the shortest time-to-live keys among those set to have an expire set.

To set the eviction policy, you can add or modify the maxmemory-policy directive in your redis.conf file, like so:

maxmemory-policy volatile-lru

You can also set this configuration at runtime using the CONFIG SET command:

127.0.0.1:6379> CONFIG SET maxmemory-policy volatile-lru
OK

Remember to replace volatile-lru with your preferred eviction policy.

Note: The lru, random and ttl eviction policies only evict keys with an expiration set if the maxmemory directive is also set to a value other than 0.