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fix: handle zero bucket counts in ExponentialHistogram merge #4459

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merged 2 commits into from
Feb 6, 2024

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mwear
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@mwear mwear commented Feb 5, 2024

Which problem is this PR solving?

This PR fixes a bug in the exponential histogram merge operation where the source histogram has empty bucket counts. The bucket index was not being set properly in this case, and depending on the histogram being merged, it can lead to corrupted counts in the resulting histogram.

Fixes #4450

Short description of the changes

Added special case handling for the zero-length bucket counts case in the _incrementIndexBy method.

Type of change

Please delete options that are not relevant.

  • Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Added a unit test that replicates a real world failure that exhibits this issue. If you comment out the changes added to _incrementIndexBy you will see the newly added test fail.

Checklist:

  • Followed the style guidelines of this project
  • Unit tests have been added
  • Documentation has been updated

@mwear mwear requested a review from a team February 5, 2024 03:31
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codecov bot commented Feb 5, 2024

Codecov Report

Merging #4459 (e4f1c85) into main (588d8ad) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files
@@            Coverage Diff             @@
##             main    #4459      +/-   ##
==========================================
+ Coverage   92.41%   92.42%   +0.01%     
==========================================
  Files         330      330              
  Lines        9514     9516       +2     
  Branches     2028     2029       +1     
==========================================
+ Hits         8792     8795       +3     
+ Misses        722      721       -1     
Files Coverage Δ
...sdk-metrics/src/aggregator/ExponentialHistogram.ts 98.13% <100.00%> (+0.01%) ⬆️

... and 1 file with indirect coverage changes

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@pichlermarc pichlermarc left a comment

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Wow, that's a tricky one! Thanks for doing the investigation and coming up with a fix so quickly @mwear 🙂

@pichlermarc pichlermarc merged commit 6d276f4 into open-telemetry:main Feb 6, 2024
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Zirak pushed a commit to Zirak/opentelemetry-js that referenced this pull request Sep 14, 2024
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Successfully merging this pull request may close these issues.

Exponential Histogram : observed bucket counts sometimes not matching with overall count
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