APIs performance: Meaning of percentile

Hi Avid Learner,

Today we're going to talk about the concept of percentile. Below is a screenshot from Grafana, which is an excellent tool to view the APIs' performance metrics. Today's article is about understanding what we mean exactly when we say e.g. 99th percentile response time of this API is Xms or for that matter, any percentile, be it 99th, 90th, 70th, 50th, or any number.

Let's see the image below first

(Image credit: https://resilience4j.readme.io/docs/grafana-1)

Let's say there are 100 values of response times and we arrange the values in ascending order. In order to compute the 90th percentile, the value at the 91st position would be the 90th percentile. In order words, 90% of the values are smaller than this value.

Importance of percentile:

The percentile gives an accurate indication of system performance as we're taking care of the worst case. Average won't be that helpful as the traffic pattern may vary with time.

Hopefully, this is clear! See you next time with the next article, till then Happy Tech Learnings!

PS: A bunch of articles e.g Circuit Breaker Design Pattern and the OAuth series already been published; do go through them if you're interested to learn more.

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