Fix minimum required bucket count for exponential histogram merging #133711
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elasticsearchmachine
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:StorageEngine/Mapping
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felixbarny
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Aug 28, 2025
...stogram/src/main/java/org/elasticsearch/exponentialhistogram/ExponentialHistogramMerger.java
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Just added test-failure label and this comment to force an automation. Normally we wouldn't add the test-failure label, but because test-failure was added originally, this ticket it getting alerted as a test failure. By adding back to label and adding a comment, it forces this ticket to no longer show up in alerts. |
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The exponential histogram merging algorithm previously did not verify the desired target bucket count for the result of the merge operation.
Because due to how exponentialhistograms work, at least for buckets are requried to represent every possible distribution:
(-Inf, -1),(-1, 0),(0, 1)and(1, +Inf).This was uncovered by a randomized test from a different PR:
https://buildkite.com/elastic/elasticsearch-pull-request/builds/88511#0198f05a-75bd-4e01-82fb-96ff2133a74e
This PR adds a fix and a reproducer test.