Redis is the default answer when an app needs sub-millisecond reads, a shared session store, a queue, or a rate limiter, and has earned that spot over fifteen years. The 2024 move to SSPL fractured trust and spawned Valkey, the Linux Foundation fork now powering AWS and Google's hosted services. The 2025 return to AGPLv3 with Redis 8 folded JSON, time series, and the query engine into core and put Redis back in the OSI tent, but the split is real. For most teams Redis is still the pick on maturity and tooling. Teams wanting permissive licensing should pick Valkey, the wire-compatible fork.
- Sub-millisecond reads and writes from an in-memory engine
- One process covers cache, queue, pub/sub, and rate limiting
- Mature clients and operators across every major language and platform
- Redis 8 folds JSON, time series, and vector search into core
- Self-hostable, with managed options on every major cloud
- Memory-bound, so large datasets get expensive fast
- Durability is best-effort, not a system of record by default
- License churn (BSD to SSPL to AGPL) left lasting community distrust
- AGPLv3 copyleft can complicate proprietary embedding
- Cluster mode adds real operational overhead at scale
Redis is an in-memory key-value store used as a cache, session store, message broker, and increasingly a vector database. It is one of the most widely deployed pieces of infrastructure in production, and after a turbulent licensing stretch it returned to an OSI-approved license with Redis 8 in 2025.
Where it fits
Redis sits alongside a primary database, not in place of one. The classic role is an in-memory cache that absorbs read traffic before it reaches Postgres or MongoDB. From there the use cases compound: a shared session and token store across stateless app servers, job queues and event streams (via Redis Streams), rate limiting on API gateways, and pub/sub for real-time fan-out. Redis 8 also ships vector sets and the Redis Query Engine, which bring vector search and semantic caching into the same process that already holds the cache. The mental model stays the same regardless of feature count: Redis is the fast, volatile layer that complements a durable store rather than replacing it.
Cost to adopt
Self-hosting the open source build is free, and a single node runs almost anywhere. The real cost is memory: Redis keeps the working set in RAM, so the bill scales with data size rather than queries. Redis Cloud is the managed first-party option, billed on memory and throughput with a free tier for small workloads. Upstash takes a different shape with serverless, per-request pricing that suits spiky or edge workloads where a always-on node would idle.
The licensing history matters before adopting. Redis shipped under BSD for fifteen years, switched to a dual RSALv2/SSPLv1 model in March 2024 to block cloud providers from reselling it, then added AGPLv3 with Redis 8 in May 2025, returning to OSI-approved status. The SSPL period triggered Valkey, a BSD-3 fork stewarded by the Linux Foundation with AWS, Google, and Oracle backing. Valkey is wire-compatible and now underpins several hosted services, so teams that need permissive licensing have a genuine drop-in path.
How it compares
PostgreSQL, A durable relational system of record, not a cache. Pair them: Postgres holds the truth, Redis fronts it for speed. Postgres adds
UNLOGGEDtables and extensions that narrow some Redis use cases, but not the latency gap.
MongoDB, A document database built for durable, queryable storage at scale. Choose Mongo when documents are the primary store. Redis is the volatile accelerant in front of it, not an alternative to it.
Turso, Edge-distributed SQLite for durable relational data close to users. Different job: Turso is the system of record at the edge, Redis is the in-memory cache and queue layer.
Valkey is the closest direct substitute, a BSD-3 fork of Redis 7.2 that stays wire-compatible and is the OSI-licensed choice for teams wary of AGPL or the commercial license history. It has no catalog entry yet.
What changed recently
Redis 8.8.0 shipped on 2026-05-25, continuing the cadence since the Redis 8 GA in May 2025 that relicensed under AGPLv3 and ended the SSPL-only period. Redis 8 folded the former Redis Stack modules (JSON, time series, probabilistic types, and the Redis Query Engine) into core, added vector sets as the first new data type in years, and landed over 30 performance improvements. Through 2025 and into 2026, Valkey kept gaining momentum as the BSD-licensed fork, with AWS and Google shifting hosted offerings to it, leaving the in-memory ecosystem split between the two lineages.
Sources
- Redis is now available under the AGPLv3 open source license, redis.io, May 1 2025
- Redis 8.8.0 release, github.com, May 25 2026
- Redis Returns to Open Source under AGPL License: Is It Too Late?, infoq.com, May 2025
- Redis vs Valkey: Understanding the Fork, oneuptime.com, Mar 31 2026