Question: What is an eviction strategy in Redis and how can it be configured?

Answer

Redis Eviction Strategy controls how keys are removed when the memory limit has been reached. This is especially important when Redis is used as a cache, and you need to decide which items should be removed first.

There are several eviction strategies available in Redis:

1. noeviction: Returns an error if the memory limit is reached and the client tries to execute commands that could result in more memory usage.
2. allkeys-lru: Removes any key trying to use the least recently used (LRU) algorithm when making room for new data.
3. volatile-lru: Removes the least recently used (LRU) keys with an expire set.
4. allkeys-random: Removes a random key when making room for new data.
5. volatile-random: Removes a random key with an expire set when making room for new data.
6. volatile-ttl: Removes the shortest time-to-live (TTL) or expire set keys first.

To configure the Redis eviction strategy, use the maxmemory-policy configuration directive. For example, if you want to set the policy to allkeys-lru, you would use:

redis-cli config set maxmemory-policy allkeys-lru

Remember to make this change persistent across Redis restarts by adding the directive to your redis.conf file:

# inside redis.conf
maxmemory-policy allkeys-lru

Please ensure to choose an eviction strategy that makes sense for your specific use-case as different applications might benefit from different strategies.