Fixed Window Counter Algorithm

For each time window, we allow a fixed request to go through.

For example, in this case. We only allow 3 requests for each micro second.

Pros and Cons

Pros

• Memory efficient
• Easy to implement

Cons

• Spikes in edges of the windows might cause more request to go in than allowed. For example:
  • In this case, we only allow 5 requests to go in per second.
  • If in the end of 2:00:00 if we have 5 requests, and then in the beginning of 2:01:00, from 2:00:30 to 2:01:30 we have 10 requests.
• To address this problem, we use
  • Sliding window log algorithm
  • Sliding window counter algorithm