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fix: span compression bug where a buffered span would not be sent when an incompressible sibling ended #3076

Merged
merged 4 commits into from
Dec 20, 2022
Merged

fix: span compression bug where a buffered span would not be sent when an incompressible sibling ended #3076

merged 4 commits into from
Dec 20, 2022

Commits on Dec 19, 2022

  1. fix: span compression bug where a buffered span would not be sent whe… 

    …n an incompressible sibling ended

https://github.com/elastic/apm/blob/main/specs/agents/handling-huge-traces/tracing-spans-compress.md#span-buffering says:
> A buffered span gets reported when
>  1. its parent ends
>  2. a non-compressible sibling ends

Before this change, case 2 was not being handled. Further, a possibly
buffered span on the ending sibling would incorrectly get sent *twice*.
The scenario is as follows:

   trans t0
     span s1: _bufferdSpan=s2
       span s2: ended, compressible -> buffered on s1
       span s3: incompressible, _bufferdSpan=s4
         span s4: ended, compressible -> buffered on s3

What happens when s3 ends? We expect:
- s4 is encoded and sent
- s2 is encoded and sent
- s3 is encoded and sent

Before this change the agent would send: s4, s4, s3

Refs: https://discuss.elastic.co/t/apm-agent-send-duplicate-record-in-mysql/321440
    @trentm
    trentm committed Dec 19, 2022
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  2. changelog entry

    @trentm
    trentm committed Dec 19, 2022
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  3. ensure we don't get .getBufferSpan() on a null parentSpan; also refac… 

    …tor to avoid numerous calls to .getParentSpan()
    @trentm
    trentm committed Dec 19, 2022
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  4. missed part of last commit (more refactoring)

    @trentm
    trentm committed Dec 19, 2022
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