Events refering to a non existing parent event are not shown in waterfall.

[simitt]

Scenario:
Testing the UI for distributed tracing with opbeans created data. Click on traces and choose opbeans-go GET /api/orders. The transaction sample shows following waterfall:

Issue:

• opbeans-python is listed as service, but not shown in waterfall. Looking into the existing documents shows that opbeans-python docs exist for this trace, but the entry transaction refers to a non-existing parent. Is it on purpose to not show all transactions and spans occuring after one event referenced a non-existing event?
  Afaik the events should still be shown, but with a message that some events are missing.

I also saw that the opbeans-python events had a timestamp ~30mins later then other events of this trace.

[elasticmachine]

Pinging @elastic/apm-ui

[felixbarny]

I don't think there is away of showing spans whose parent is missing. We can only add a warning on the trace level that there are spans missing.

The problem is that we don't know where to put the span tree. Especially when we have the tree navigation (#20660).

[jasonrhodes]

@simitt if possible, can you provide a link to this problem (minus hostname and I can load it locally or in the cloud instance)? I suspect this is just the services legend problem but your description makes it sound like it might be more than that, so I'd like to take a look. Thanks!

[simitt]

@jasonrhodes I tested this locally, so I cannot link to that unfortunately. However, I have a copy of the docs if that helps.
You should be able to reproduce this by taking any existing trace and delete a transaction in the middle of the trace. All spans and transactions that are (in-)direct children of the deleted transaction don't show up anymore in the waterfall.

[jasonrhodes]

@simitt thanks for the info. @alvarolobato this sounds like a different issue but one that would take some thinking, so probably not for 6.5, if you want to move this ticket wherever it should go to be thought about post-6.5 release.

[alvarolobato]

Are the missing spans from the node-agent? @watson could this be related to the issue you are working on?

[simitt]

@alvarolobato elastic/apm#9 is the related issue (also linked above).

[sorenlouv]

I agree with @felixbarny comment:

I don't think there is away of showing spans whose parent is missing. We can only add a warning on the trace level that there are spans missing.
The problem is that we don't know where to put the span tree. Especially when we have the tree navigation (#20660).

Since we construct the tree structure top-down, spans that don't have any parent will be orphans and never included. AFAICT there is no way for us to add them to the tree.

I'm fine with keeping the current behaviour, and leaving out spans whose parent is missing. At the very least for the upcoming release. In the future we could add a message about missing transactions/spans like in #24320

Any objections?

@makwarth @formgeist ?

[formgeist]

We agreed on this approach a while back, so 👍

[sorenlouv]

Cool, did we write this down anywhere, and can I close this issue?

[sorenlouv]

Superseeded by #25117