Compute top-level span in tracer#2137
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## fix-tag-helper #2137 +/- ##
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Coverage 97.52% 97.53%
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Files 1040 1040
Lines 53991 54005 +14
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+ Hits 52656 52672 +16
+ Misses 1335 1333 -2
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This PR is the first step towards early top level detection in the tracer.
As a preamble, the definition of top-level span is:
After the introduction of the
service_entryattribute in #2080, now know how to calculate the effective top-level spans in a trace, exactly how the agent does. Both the tracer and agent must follow the definition in previous paragraph.For every trace received, the agent calculate the top-level spans and tags them with
_dd.top_level.This is the default case. But if we send a special header, (
Datadog-Client-Computed-Top-Level), the agent will skip calculating the top-level spans itself.With this PR, this is he trace timeline:
_dd.top_levelmetric.This means that the traces are effectively the same, but each top-level span received the tagging,
span.set_metric('_dd.top_level', 1.0), twice, having no ill-effect.Follow up work
Introduce the special header https://github.com/DataDog/datadog-agent/blob/b4542cc65a1289cfe72903e52c9ed4d219d6453b/pkg/trace/api/api.go#L359-L361 to allow for the Agent to completely skip top-level calculation.