Choose Memcached when all you need is a fast, simple cache for small chunks of data, such as database results or rendered pages, spread across servers that don't talk to each other. Choose Redis when you want more than a cache: rich data structures, optional persistence to disk, replication, streams and vector search. The licence story has changed too: Redis 8 and later can be used under the AGPLv3, an OSI-approved open source licence, alongside RSALv2 and SSPLv1.
Caching advice online is often years out of date, so I read Redis's about, licences and open source pages and Memcached's home, about and documentation pages, plus its licence file, to see where each one stands now.
Redis and Memcached side by side
| Redis | Memcached | |
|---|---|---|
| Type | In-memory database for caching, vector search and NoSQL | Distributed memory object caching system |
| Data model | 18 data structures in Redis 8, including JSON, streams and vector sets | Simple key/value; you upload pre-serialised data |
| Keeping data | Snapshots, an append-only log, or no persistence | An LRU cache by default, with items that expire |
| Replication | Built in, plus Redis Sentinel and Redis Cluster | None; servers are unaware of each other |
| Licence | RSALv2, SSPLv1 or AGPLv3 from Redis 8 | BSD-style licence |
| Latest release named | Redis Open Source 8.8 | 1.6.45 |
| Free option (as of October 2026) | Redis Open Source is free | Yes, it's open source |
The Redis licence change many guides miss
For a while the standard line was that Redis had stopped being open source. Its licences page now tells a different story. Starting with Redis 8, you can choose between three licences for Redis Open Source: the Redis Source Available License v2, the Server Side Public License v1, and the GNU Affero General Public License v3, which the page notes is an OSI-approved open source licence. Redis 7.2.x and earlier versions sit under their older terms.
Here's the detail that shows how recent the change is: Redis's own about page still mentions only RSALv2 and SSPLv1. If you're checking licences for a client project, read the licences page, not the about page. RSALv2's main limit is that you can't commercialise the software or offer it to others as a managed service.
Memcached's deliberately simple design
Memcached's documentation sets out a design philosophy that explains everything about it. The server doesn't care what your data looks like and doesn't understand data structures, so you upload data that's already serialised. Half the logic lives in the client, which chooses the server for each key. Servers are disconnected from each other, with no crosstalk, synchronisation or replication, so adding servers simply adds memory. Every command is built to be O(1), and queries on slow machines should run in well under 1ms.
It also treats forgetting as a feature: by default it's a Least Recently Used cache, and items expire after a set time. Memcached was originally developed by Brad Fitzpatrick for LiveJournal in 2003, and its licence file carries a BSD-style copyright notice from Danga Interactive.
What Redis adds beyond caching
Redis describes itself as an in-memory database rather than just a cache. It offers strings, hashes, lists, sets, sorted sets, bitmaps, hyperloglogs, geospatial indexes and streams, with atomic operations on them, plus replication, Lua scripting, transactions, pub/sub and keys with a time to live. You can persist data by dumping snapshots to disk or by appending each command to a log, or switch persistence off for a pure cache. Redis 8 bundles Redis Search and lists 18 data structures, including JSON and vector sets. One practical note: Redis recommends Linux for deployment and says there's no official support for Windows builds.
Pick in five questions
- Do you only need to cache rendered pages or query results? Memcached does that with very little to manage.
- Do you need lists, sorted sets, streams or JSON in memory? Redis.
- Must the data survive a restart? Redis can persist to disk; Memcached is built to forget.
- Do you want built-in replication and failover? Redis has Sentinel and Cluster.
- Are licence terms a concern for a hosted product you sell? Read Redis's licences page, or use Memcached's BSD-style licence.
Caching is one part of a fast stack, so see my guide to what to look for in developer productivity tools, and if your cache sits between several systems, these notes on data integration challenges will help.
My advice on Redis or Memcached
If you're adding a cache to a busy website and that's all, Memcached is lean and hard to break, and its design means there's little to tune. If there's any chance you'll want queues, leaderboards, sessions that survive restarts or vector search later, start with Redis now rather than migrating later. Either way, check the licence that applies to the exact version you deploy, because Redis's terms differ before and after Redis 8.
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Frequently asked questions
Is Redis open source?
From Redis 8, Redis Open Source is available under a choice of RSALv2, SSPLv1 or AGPLv3, and the Redis licences page notes that AGPLv3 is an OSI-approved open source licence.
Is Memcached free?
Yes. Memcached describes itself as free and open source, and its licence file carries a BSD-style notice from Danga Interactive.
Does Memcached save data to disk?
Memcached's docs describe it as a Least Recently Used cache where items expire after a set time. Redis is the one that offers snapshots and an append-only log.
Does Redis run on Windows?
Redis says Linux and macOS are where it's developed and tested most, recommends Linux for deployment, and says there's no official support for Windows builds.
Who created Memcached?
Memcached was originally developed by Brad Fitzpatrick for LiveJournal in 2003.
