Redis TTL Calculator

TTL (Time To Live) is the expiration time for a Redis key. After the TTL expires, Redis automatically deletes the key. Set it with EXPIRE key seconds or EXPIREAT key unix-timestamp. Check remaining TTL with TTL key (returns -1 if no expiry, -2 if key doesn't exist).

EXPIRE key seconds — set TTL in seconds. PEXPIRE key milliseconds — set TTL in milliseconds. EXPIREAT key timestamp — expire at Unix timestamp. PEXPIREAT key milliseconds-timestamp — expire at ms timestamp. SET key value EX seconds — set value with TTL atomically. In Redis 7.0+, EXPIRE supports NX/XX/GT/LT options.

It depends on data volatility and acceptable staleness: Real-time data (stock prices, live scores): 1-5 seconds. Session tokens: 15-30 minutes. User profile cache: 5-15 minutes. Product catalog: 1-6 hours. Static reference data (countries, categories): 24 hours. Computed aggregates (daily stats): until next compute cycle.

Cache stampede happens when many keys expire simultaneously, causing all requests to hit the database at once. Solutions: 1) Jitter — add random offset to TTL (base + rand(0, jitter)). 2) Probabilistic early expiration — start refreshing before expiry. 3) Background refresh — never let cache miss hit the DB directly. 4) Lock with SETNX — only one process refreshes, others wait.