SET with EX/PX — Atomic Set+Expire

Setting a key and its expiry should be atomic. SET key value EX 10 does both in one command.

Extended SET Syntax

SET key value [EX seconds] [PX milliseconds] [NX|XX]

• EX seconds — expire in N seconds
• PX milliseconds — expire in N milliseconds
• Can combine with NX/XX: SET key value EX 10 NX

PTTL

PTTL key returns remaining TTL in milliseconds (vs TTL which returns seconds).

Why Atomic?

Without atomic set+expire, there's a race condition:

1. SET key value → succeeds
2. Server crashes before EXPIRE key 60
3. Key lives forever — a memory leak

SET key value EX 60 can't have this problem.