How it works
Redis keeps data in memory and maps keys to values: strings, lists, sets, sorted sets, hashes and streams. Because nothing waits on a disk, reads and writes are extremely fast, which makes it the usual choice for a cache in front of a slower database, for session storage and for counting things such as requests per minute.
It can save to disk, but it is usually a fast helper beside a main database rather than the only copy of important data. A 2024 licence change led to Valkey, a fully open-source fork under the Linux Foundation, and Redis later added an AGPL option. Upstash and Redis Cloud host it for you.
Redis pros and cons
Pros
- Extremely fast, with rich data structures
- Simple to use for caching, sessions and rate limiting
- Built-in pub/sub, streams and keys that expire on their own
Cons
- Memory costs more than disk, so large datasets get expensive
- Not a replacement for a durable main database
- Licence changes mean checking which flavour (Redis or Valkey) you run
When to use Redis
Pick it when
- Caching slow queries or API responses
- Rate limits, sessions, leaderboards and short-lived data
- Simple job queues and real-time counters
Skip it when
- It would be the only copy of data you cannot afford to lose
Redis pricing
Open source
Free to run yourself. Redis Cloud has a free 30 MB database and paid plans from about $5 a month; Upstash bills per request.
Redis pricing page (opens in a new tab)Approximate, checked September 2026.What the other tools cost
Related terms
More in Databases and storage
Document and key-value