Fixed window algorithm in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Fixed Window Algorithm in rate limiting?

It is a method to limit the number of requests a user can make in a fixed time period, like allowing 100 requests per minute. If the limit is reached, further requests are blocked until the next time window starts.

beginner

How does the Fixed Window Algorithm count requests?

It counts all requests within the current fixed time window, for example, from 12:00:00 to 12:00:59. When the window ends, the count resets to zero for the next window.

intermediate

What is a downside of the Fixed Window Algorithm?

It can cause bursts of traffic at the edges of windows. For example, a user can send the maximum allowed requests at the end of one window and again at the start of the next, effectively doubling the allowed rate temporarily.

beginner

In the Fixed Window Algorithm, what happens when the request count exceeds the limit?

The system rejects or delays further requests until the current time window ends and the count resets.

beginner

Why is the Fixed Window Algorithm easy to implement?

Because it only needs to track the count of requests in a simple fixed time window, without complex calculations or storing timestamps for each request.

What does the Fixed Window Algorithm use to limit requests?

A A fixed time period to count requests

B A sliding time window

C Random request sampling

D User IP address only

The Fixed Window Algorithm counts requests in a fixed time period, like one minute.

What happens when the request count reaches the limit in a fixed window?

A Requests are always allowed

B Requests are blocked until the window resets

C Requests are queued indefinitely

D The limit increases automatically

Once the limit is reached, further requests are blocked until the next time window.

What is a common problem with the Fixed Window Algorithm?

A It allows bursts of requests at window edges

B It requires complex calculations

C It never resets the count

D It blocks all requests

Users can send many requests at the end of one window and start of the next, causing bursts.

Which of these is NOT true about the Fixed Window Algorithm?

A It limits requests per fixed time period

B It resets the count after each time window

C It is simple to implement

D It tracks requests individually with timestamps

The Fixed Window Algorithm does not track individual timestamps, only counts per window.

Why might someone choose the Fixed Window Algorithm?

A Because it perfectly smooths request rates

B Because it never blocks requests

C Because it is easy and fast to implement

D Because it tracks each request's exact time

Its simplicity and speed make it a common choice despite some limitations.

Explain how the Fixed Window Algorithm controls the number of API requests.

Think about counting requests in a set time and what happens when the limit is reached.

Describe one advantage and one disadvantage of the Fixed Window Algorithm.

Consider simplicity and how traffic might spike.