Information:

Environment

  • Dynatrace Portal
Symptoms

Why do I see an overlap between Connection and First Byte time in the waterfall charts?

Solution

The database for the Dynatrace Portal stores two types of data for every collected metric:

  • The download time, stored as an integer.
  • The time stamp when the event occurred (in GMT).

When aggregating and reporting on these metrics, the Dynatrace Portal uses the integer value. However, in the waterfall chart, the time stamp of the metric also plays a role.

Because of a known limitation with SQL Server and time stamps, the best precision SQL Server can offer is 3 milliseconds. This means that even though the agent might report a first byte start time of 2/22/2016 09:10:11.012, the time is rounded down to 2/22/2016 09:10:11.01.

This rounding issue can occasionally make the First Byte Time look as if it started before the connection has been established (i.e., before the Connection Time is completed).

This issue only occurs in tests where the total test time is extremely short. When the total response time is within 2–3 seconds, a difference of milliseconds combined with the rounding issue described above may result in the apparent overlap of the metrics in the waterfall chart.

 

Root Cause

 

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