Apdex is an industry standard to measure users' satisfaction with the response time of an application or service. It's a simplified Service Level Agreement (SLA) solution that gives application owners better insight into how satisfied users are, in contrast to traditional metrics like average response time, which can be skewed by a few very long responses.
Apdex is a measure of response time based against a set threshold. It measures the ratio of satisfactory response times to unsatisfactory response times. The response time is measured from an asset request to completed delivery back to the requestor.
The application owner defines a response time threshold T. All responses handled in T or less time satisfy the user.
For example, if T is 1.2 seconds and a response completes in 0.5 seconds, then the user is satisfied. All responses greater than 1.2 seconds dissatisfy the user.
Apdex tracks three response counts:
The Time calculation will change based on your own app's T setting. In the following example, T = 1.2 seconds.
|Level||Multiplier||Time (T Example = 1.2)|
|Satisfied||T or less||<= 1.2 seconds||Tolerated||>T, <= 4T||Between 1.2 and 4.8 seconds|
|Frustrated||> 4T||Greater than 4.8 seconds|
Note: Your configuration file's
apdex_f value is four times your app server's Apdex T value. This threshold is useful, for example, with transaction tracing. For more information, see the configuration file documentation for your New Relic agent.
The Apdex score is a ratio value of the number of satisfied and tolerating requests to the total requests made. Each satisfied request counts as one request, while each tolerating request counts as half as satisfied request.
(170 + (20/2))/200 = 0.9.
Note: You can download this diagram and example [PDF].
Errors frustrate your users. Any request that raises a server-side error is considered a frustrating response, no matter how fast it returns to the user. Nobody likes to see a "500: Application Error" page. This makes it possible to have an average response time that is well below the Apdex T but still have a poor Apdex score.
The dissatisfaction percentage is the percentage of the total dissatisfaction experienced by the app's users that is contributed by this transaction.
(Frustrations(App) + Tolerations(App)/2)
If a transaction is always frustratingly slow but rarely visited, it will not contribute much to the app's total dissatisfaction. Conversely, if a transaction normally is fast (for example, Apdex 0.95) but has high throughput, this may contribute a large proportion of the app's dissatisfaction simply because it contributes a large proportion of your app's traffic.
Additional documentation resources include:
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