How is the response time contributions calculated in complex service flows?

[kevin_aird]

I have been trying to explain to a project how response time
contribution is calculated in a Service Flow diagram. I have been referring to
this answer but came across an inconsistency in the calculation results for
more complex service flows. Can someone please tell me how response time
contributions are calculated and why my calculations seem to be off in Example
#2 attached?

Excel calculations examples-calcs.xlsx

In Example 1 –

• In
  this case I am using the service flow for a single PurePath


• The
  calculations in this case are mostly adding up – The response time
  contribution calculation matches the contribution reported in the service
  flow

In Example 2 –

• For
  this case I use a service flow analyzing approx. 2k transactions.


• Using
  the same formulas from example 1, the response time contributions no longer
  match what we're seeing in the Service Flow


• There's
  some asynchronous invocations in play here. But even the contribution
  calculation for the Web Tier, which is upstream to the async calls, does
  not match what is reported in the service flow

The formulas I'm
using:

• (Average
  time per Tier) = (Average
  Response Time) x (Call Percentage) x (Calls per request)
• (Calls per request) = (Requests) / (Consuming API.Requests)
• (Response Time Contribution) = (Average time per Tier) /
  (Consuming API.Average Response Time)

Note: The first formula I got from this answer: https://answers.dynatrace.com/questions/200720/how-is-the-response-time-contribution-in-service-f.ht...

[skrystosik]

I understand this like this

We have something like this:

Root —- A(60%) —- B (70%). —- C (20%)

This means that on A we spent 60%, from this time 70% was spent on component B (from root it will be x*0.6*0.7)

From this time 20% was spent on component C so x*0.6*0.7*0.2

Sebastian

[kevin_aird]

Thanks for the reply Sebastian. So please correct me if I'm misinterpreting your answer. But from that I'm getting this formula:

(Average Time on C) = (Average Time on Root) x (Response time Contrib on A) x (Response time Contrib on B) x (Response time Contrib on C)

which becomes this formula (when trying to get the contribution time on C):

(Response time Contrib on C) = (Average Time on C)/( (Average Time on Root) x (Response time Contrib on B) x (Response time Contrib on A) )

When I try to apply this new formula to the two examples in my note however, the results still do not match the response time contributions reported on the Dynatrace Servce Flow. Are there any other factors I'm missing here?