Redis is an open-source, in-memory data structure store used as a database, cache, and message broker. It keeps data in RAM and supports strings, hashes, lists, sets, sorted sets, and streams.
Why it matters
Because data lives in memory, Redis answers in well under a millisecond, which makes it ideal for caching, session storage, rate limiting, leaderboards, and job queues. It can persist data to disk through snapshots or an append-only log, but its main strength is speed rather than large durable storage. Memory is the limiting resource, so eviction policy matters.
Example
redis-cli -h 127.0.0.1 -p 6379
> SET session:abc "user:42" EX 3600
> GET session:abc
> INCR hits:homeEX 3600 makes the key expire after an hour.
Common mistakes
- Leaving Redis open on port 6379 without a password or network restriction.
- Using it as the only copy of important data without enabling persistence.
- Storing keys with no expiry, so memory slowly fills until eviction or failure.
Related
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