Memcached

Memcached is a high-performance, distributed memory object caching system. It is simpler than Redis. It does arguably one thing: Key-Value caching of strings/objects in RAM.

When to Use

• Simple Caching: Pure LRU cache.
• Multi-Threaded: Memcached is multi-threaded (Redis is single-threaded). It scales vertically better on massive multicore machines for simple GET/SET throughput.
• Session Cache: Storing web sessions.

Quick Start

# Telnet interface
set mykey 0 60 4
data
STORED

get mykey
VALUE mykey 0 4
data
END

Core Concepts

Slab Allocation

Memcached manages memory in “Classes” of chunks (Slabs) to prevent fragmentation.

LRU (Least Recently Used)

When full, it evicts the oldest unused items.

No Persistence

If you restart, data is gone.

Best Practices (2025)

Do:

• Use for huge read-heavy loads: Facebook uses it heavily.
• Use Serialization: Store Protobuf or msgpack for efficiency.

Don’t:

• Don’t use as a Datastore: It is a cache only.
• Don’t use iterating: You cannot “List all keys”. You must know the key to get the value.
• Comparison to Redis: In 2025, Redis is generally preferred for features. Use Memcached if you specifically need multi-threaded scaling for pure String caching.

References

• Memcached Wiki