LLM Best Practices

Redis vs Memcached

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Overview

Pick Redis or Valkey for new caches; keep Memcached only where a simple, multi-threaded key-value cache is all you need and you already operate it. The licensing picture changed: Redis 7.2 and earlier are BSD-3; Redis 7.4 is RSALv2 or SSPLv1; Redis 8 adds AGPLv3 (OSI-approved) as a third option. Valkey, the Linux Foundation fork, is BSD-3 and at 9.1 (2026-05-19). Memcached is at 1.6.45 (2026-07-09). Amazon ElastiCache offers Valkey, Redis OSS, and Memcached.

Comparison

DimensionRedis 8 / Valkey 9Memcached 1.6
Data modelStrings, hashes, lists, sets, sorted sets, streamsKey to blob values
PersistenceRDB snapshots and AOFNone; restart empties the cache
MessagingPub/sub and Streams with consumer groupsNone
Atomic logicTransactions and Lua scriptingcas and counters
ClusteringServer-side Redis Cluster / Valkey clusterClient-side sharding
ThreadsCommand loop plus I/O threadsMulti-threaded
LicenseRedis 8: RSALv2, SSPLv1, or AGPLv3; Valkey: BSD-3BSD
ManagedElastiCache (Valkey, Redis OSS), Redis Cloud, UpstashElastiCache

Pick Redis or Valkey when

Pick one of them for almost every new service.

  • Sessions with TTL, rate limiting with INCR and EXPIRE, idempotency keys, and locks with SET key value NX PX.
  • Leaderboards and rankings with sorted sets; queues and event logs with Streams.
  • Data you want to survive a restart, or replicate to a standby.
  • License fit: use Valkey or Redis 7.2 and earlier for permissive BSD terms; use Redis 8 under AGPLv3 only if your legal team accepts its network-use clause. RSALv2 and SSPLv1 restrict offering the software as a managed service.

Pick Memcached when

Pick Memcached for narrow, plain caching.

  • Only get, set, delete, and cas on opaque values, with no durability.
  • An existing Memcached fleet that works; replace it when a feature needs Redis semantics.
  • Strongly multi-threaded access to one cache node is the bottleneck you measured.

Migrate

Memcached to Redis or Valkey: swap the client library and let the cache warm; no data migrates because Memcached holds no durable state. Run both during a soak period and compare hit rates. Redis to Memcached means flattening every structure to serialized values and dropping scripts, persistence, and pub/sub; do it only for a measured memory or cost reason. For durable key-value storage at scale on AWS, compare dynamodb-vs-postgres.

FAQ

Should I use Redis or Memcached for a new cache?

Use Redis or Valkey for almost every new service, since they add data structures, persistence, pub/sub, and Streams. Keep Memcached only for a plain multi-threaded key-value cache you already operate.

Is Redis still open source?

Redis 8 adds AGPLv3, an OSI-approved license, alongside RSALv2 and SSPLv1; Redis 7.4 is RSALv2 or SSPLv1 only, and Redis 7.2 and earlier are BSD-3. For permissive BSD terms, use Valkey or Redis 7.2 and earlier.

What is Valkey and should I use it instead of Redis?

Valkey is the Linux Foundation fork of Redis, licensed BSD-3 and at 9.1 (2026-05-19). Use it when you want Redis semantics under permissive terms; ElastiCache offers it alongside Redis OSS and Memcached.

Is Memcached faster than Redis?

Memcached is multi-threaded, so pick it only when multi-threaded access to one cache node is a bottleneck you measured. Redis runs a command loop plus I/O threads and covers far more use cases.

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