Redis Command Cheatsheet

Redis (Remote Dictionary Server) is an in-memory data structure store used as a database, cache, and message broker. Its key strengths are sub-millisecond read/write performance and rich data types: strings, lists, hashes, sets, sorted sets, streams, and more. Common use cases include session storage, rate limiting, pub/sub messaging, leaderboards (sorted sets), job queues (lists), and full-page caching.

KEYS pattern returns all matching keys in one blocking call. In production with millions of keys, KEYS can block the Redis server for seconds, causing timeouts. SCAN is the safe alternative — it iterates the keyspace in small batches (cursor-based) without blocking. Always use SCAN in production. SCAN returns a cursor and a batch of keys; repeat until cursor returns 0.

O(1) means the command takes constant time regardless of data size — it is always fast. O(N) means the time scales linearly with N (number of elements). For example, LRANGE with a list of 1 million items is O(N) and can be slow. In Redis, O(N) commands on large data structures are a common source of latency spikes. Always check complexity before using commands like KEYS, SMEMBERS, or HGETALL on large data.

EXPIRE key seconds sets a timeout on a key — Redis will automatically delete it after that many seconds. TTL key returns the remaining time-to-live in seconds (-1 means no expiry, -2 means the key does not exist). PEXPIRE and PTTL are the millisecond equivalents. Use PERSIST to remove an expiry and make a key permanent again.