What is the Apdex value when a service is down?

Question

Apdex is an industry-standard to measure users' satisfaction with the response time of web applications and services, as shared by the New Relic document

https://docs.newrelic.com/docs/apm/new-relic-apm/apdex/apdex-measure-user-satisfaction/

For formula I derived from the document is like (A + B/2)/C where

• A = requests meeting the perforcemance
• B = requests meeting half the performance
• C = the total requests

(A + B <= C).

My question is when the service is down, what happens to the Apdex value? Does it goes infinity i.e 0/0 .... or it is handled as 0?

I'm trying to figure out if Apdex value can help to detect the system down.

Answer 1

When a system is down, users change their behaviour. Some users might try again and again, waiting for the service to be available, some might give up:

• Those who try repeatedly will be counted as unsatisfied.
• Those who give up, will no longer be counted. That is - in a way - sensible, because they are already frustrated enough to give up. Conceptual, there is only a small difference between a user giving up because a request takes to long and a user giving up, because the system is down.

I don't think it is sensible to use the Apdex value to determine if a system is down. I'd rather think, it is the other way around: Users will almost certainly be disappointed.