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Add spec for 'span.sync' field #802

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Jun 8, 2023
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Add spec for 'span.sync' field #802

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2a87148
add spec for 'span.sync' field
SylvainJuge Jun 1, 2023
c08703d
clarify per-platform behavior in UI
SylvainJuge Jun 6, 2023
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11 changes: 11 additions & 0 deletions specs/agents/tracing-spans.md
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Expand Up @@ -33,6 +33,17 @@ Each span will have a `name`, which is a descriptive, low-cardinality string.

If a span is created without a valid `name`, the string `"unnamed"` SHOULD be used.

### Span `sync`

Span execution within a transaction or span can be synchronous (the caller waits for completion), or asynchronous (the caller does not wait
for completion).
Comment on lines +38 to +39
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Maybe here we should clarify that the agents should only be able to capture the (a)synchronous "nature" of a specific span, for example when a synchronous or asynchronous API is used.

It might sound obvious, but if an asynchronous span is (mis)used in a synchronous way this can't easily be detected by agents at runtime, so from the user perspective it's only in the "shape" of the trace and the relative position of the blocking or async spans that we can infer if that's an issue or not.

Few examples:

  • an asynchronous API is used in a blocking way: having the async span making the parent span/transaction longer indicates that refactoring code could help.
  • starting multiple async tasks from a single span/transaction and then awaiting their completion in a blocking way would not be considered a problem because the async tasks are started in parallel. However, doing the same with a single span would make it fall in the "async API used in a blocking way" described above.


In UI:

- when `sync` field is not present or `null`, we assume it's the platform default and no badge is shown.
- when `sync` field is set to `true`, a `blocking` badge is shown in traces where the platform default is `async`: `nodejs`, `rum` and `javascript`
- when `sync` field is set to `false`, an `async` badge is shown in traces where the platform default is `blocking`: other agents

### Span outcome

The `outcome` property denotes whether the span represents a success or failure, it is used to compute error rates
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