Parent span timestamp is pined at service start moment or the child request sent moment?

[bigbanglwb]

Skywalking agent can avoid modify code so I used it. However, I am confused about when the timestamp is pined?
Take an example, now I have 2 service, named as "Parent Service" and "Child Service".

• When a client request come to "Parent Service", it map to a controller ( like Spring boot) , it will do some work and send an request to "Child Service".
• "Child Service" got the request and return the response to "Parent Service".
• "Parent Service" wait the "Child Service" response and do some work, then it return response to client.

Exit span belongs to "Parent Service", and entry span belongs to "Child Service", so I want to know exit span' s start timestamp is pined at the moment of "parent service" got the client request or the moment of "Parent Service " sent the request to "Child Service". Also, is the same true of the end time?

I have read serval blog and discussion but still confused. I would be very grateful if you could reply my question.

[wu-sheng]

The time is just on the minute level, so, I would not be surprised if they are the same. Even visualizing in ms, they could be the same too.

I am not sure what is your question actually, this has nothing related to skywalking, it is just the reality of the time.

[bigbanglwb]

The picture is not my doubt, it just take example for the relationship of "Parent Service" and "Child Service"

[wu-sheng]

Then, what is the actual question?

[bigbanglwb]

Sevice A send an request toService B . My question is when the service A 's exit span is created and ended ?

[wu-sheng]

That depends on which plugin you are using. Exit span is created by the HTTP client plugin.

[pg-yang]

Exit span belongs to "Parent Service", and entry span belongs to "Child Service", so I want to know exit span' s start timestamp is pined at the moment of "parent service" got the client request or the moment of "Parent Service " sent the request to "Child Service". Also, is the same true of the end time?

Parent Service include two component usually , receiver or sender , like spring mvc controller and apache HttpClient .
For Parent Service, It create a Entry span when receive a request , and create Exist span when send a request by HttpClient

[bigbanglwb]

Thank you, your answer is completely solve my question! So can I think that parent service exit span will very similar to entry span? Because their send time and recv time is similar.

I mean, is the parent service exit span end timestamp pined when received the child service response?

As the figure shows, I am confused about why the exit span is much longer than entry span. It just caused by wrong code?

[pg-yang]

+-------------+         +------------------+            +-------------------------+
|   Browser   |         |  Case Servlet    |            | ContextPropagateServlet |
|             |         |                  |            |                         |
+-----|-------+         +---------|--------+            +------------|------------+
      |                           |                                  |
      |                           |                                  |
      |       WebHttp            +-+                                 |
      +------------------------> |-|         HttpClient             +-+
      |                          |--------------------------------> |-|
      |                          |-|                                |-|
      |                          |-|                                |-|
      |                          |-| <--------------------------------|
      |                          |-|                                +-+
      | <--------------------------|                                 |
      |                          +-+                                 |
      |                           |                                  |
      |                           |                                  |
      |                           |                                  |
      |                           |                                  |
      +                           +                                  +

Case Servlet receive a request will create entrySpan , And close the span when it finish all work . HttpClient's exitSpan is A Child span of entrySpan .
Generally speaking， HttpClient exist span close when it receive response.
And Case Servlet entrySpan Close when it reponse client complete 。
https://skywalking.apache.org/docs/skywalking-java/latest/en/setup/service-agent/java-agent/plugin-test/