Sliding Window Rate Limit
ELI5 — The Vibe Check
Sliding window rate limiting counts requests in a moving time window instead of fixed buckets. With fixed windows, you could make 100 requests at 11:59 and 100 more at 12:00 — 200 in two seconds! Sliding window prevents this by always looking back exactly N minutes from right now. It's like a rolling average that smooths out the spikes.
Real Talk
Sliding window rate limiting combines the simplicity of fixed windows with the accuracy of per-request tracking. It uses weighted counting from the previous and current fixed window to estimate the request count in the sliding window. This prevents the boundary burst problem of fixed window counters while being more memory-efficient than per-request log-based approaches.
When You'll Hear This
"Switch to sliding window — clients are gaming the fixed window boundaries." / "The sliding window counter uses Redis sorted sets for efficient counting."
Related Terms
Fixed Window
Fixed window rate limiting counts requests in fixed time blocks (e.g., per minute). Simple: reset the counter every 60 seconds. The catch?
Leaky Bucket
A leaky bucket processes requests at a fixed rate, like water dripping from a bucket. No matter how fast requests pour in, they come out at a steady drip.
Rate Limiter
A rate limiter controls how many requests someone can make to your API in a given time window. It's the bouncer who says 'you've had enough — come back in
Token Bucket
A token bucket is a rate limiting algorithm. Imagine a bucket that fills with tokens at a steady rate. Each request costs one token.