INCR & DECR — Atomic Counters

Redis can treat string values as integers and atomically increment or decrement them.

Commands

Behavior

• If the key doesn't exist, treat it as 0 before operating
• Returns the new value as RESP integer: :<value>\r\n
• If the stored value isn't a valid integer: -ERR value is not an integer or out of range\r\n

Why This Matters

Atomic counters are used everywhere: page views, rate limiting, leaderboard scores, inventory counts. The atomicity guarantee means no race conditions — critical in concurrent systems.

Implementation

Parse the stored string to an integer, perform the operation, store back as string. The key insight: Redis stores everything as strings internally but interprets them as integers when needed.