All 7 Rate Limiting with Redis questions
More in Rate Limiting with Redis
What is rate limiting, and why is Redis a good fit for implementing it? How do you implement a basic fixed window rate limiter using Redis's INCR and EXPIRE commands? What is the token bucket algorithm for rate limiting, and what advantage does it offer over a simple fixed window counter? How do you provide helpful feedback to API consumers about their current rate limit status, such as how many requests they have remaining? How would you implement a distributed rate limiter using Redis that works correctly across multiple application servers handling requests for the same user? How would you design a tiered rate limiting system that applies different limits based on a user's subscription plan?
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Redis › Rate Limiting with Redis

What is the sliding window log algorithm for rate limiting, and how can it be implemented using a Redis sorted set?

Intermediate

Answer

The sliding window log algorithm stores a timestamp for every single request in a sorted set, removes timestamps older than the allowed window before checking the current count, and rejects the request if too many timestamps remain within the current window, providing more accurate rate limiting than a fixed window since it does not have a hard reset boundary that can be gamed.
ZREMRANGEBYSCORE requests:user123 0 (current_time - 60)
ZADD requests:user123 current_time current_time
ZCARD requests:user123
Real-world example A payment API uses a sliding window log to precisely enforce ten requests per minute per customer, correctly preventing a burst of requests that would otherwise slip through right at a fixed window's reset boundary.

Common follow-ups: What is the memory cost of storing a timestamp for every single request?;How does this approach compare in accuracy to a simpler fixed window counter?

Sets & Sorted Sets in Redis;Data Types
All 7 Rate Limiting with Redis questions