Memcached versus Redis

In short: Both keep data in RAM for fast access. Memcached is a plain key-value cache, Redis a data-structure server with many more features.

In more detail: For pure caching of page fragments or query results Memcached is enough. As soon as you need lists, counters, queues or durability, Redis is the choice.

In Depth

• Memcached: Strings as values, multi-threaded, simple distribution across servers done by the client (consistent hashing), no storage on disk.
• Redis: Strings, lists, sets, sorted sets, hashes, streams. Optional persistence (RDB snapshots, AOF log), replication, pub/sub, Lua scripts. The core is largely single-threaded.
• Eviction: Both delete by rules such as LRU when memory is full.
• Typical Redis jobs: Sessions, leaderboards (sorted set), rate limiting, job queues.
• Choice: Pure cache with very high throughput on many cores: Memcached. Anything beyond: Redis.

See also: Caching strategies