Fix distributor rebatch bug #5186
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… only for ring sharding (as required)
joe-elliott
reviewed
May 29, 2025
joe-elliott
reviewed
May 29, 2025
| @@ -472,7 +471,7 @@ func (d *Distributor) PushTraces(ctx context.Context, traces ptrace.Traces) (*te | |||
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| maxAttributeBytes := d.getMaxAttributeBytes(userID) | |||
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| keys, rebatchedTraces, truncatedAttributeCount, err := requestsByTraceID(batches, userID, spanCount, maxAttributeBytes) | |||
| ringTokens, rebatchedTraces, truncatedAttributeCount, err := requestsByTraceID(batches, userID, spanCount, maxAttributeBytes) | |||
joe-elliott
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May 29, 2025
knylander-grafana
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Jun 2, 2025
* Fix distributor rebatch bug, by not using a 32-bit hash for deduping, only for ring sharding (as required) * lint * changelog
mdisibio
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* Fix distributor rebatch bug, by not using a 32-bit hash for deduping, only for ring sharding (as required) * lint * changelog
carles-grafana
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* Fix distributor rebatch bug, by not using a 32-bit hash for deduping, only for ring sharding (as required) * lint * changelog
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What this PR does:
Distributors rebatch incoming writes by trace ID, in order to ensure that all spans for a given trace end up on the same ingesters over time. It's using a 32-bit hash which can lead to collisions. When 2 traces in the incoming write request have the same hash (collide), their spans will get intermixed, i.e. bad data.
The core issue is that the distributor logic was conflating hashing for the ring, and hashing for dedupe. These don't need to be the same hash, nor should they be. Because the ring requires 32-bit hashes and collisions there don't matter, it just means 2 traces go the same ingesters (normal and unavoidable).
But collisions for dedupe must be avoided, and we do this by swapping that part to a 64-bit hash. Same approach as in trace combiner for spans, and there are test cases for known trace ID collisions under the old method and a test to check the collision rate of the new method.
Which issue(s) this PR fixes:
Fixes #
Checklist
CHANGELOG.mdupdated - the order of entries should be[CHANGE],[FEATURE],[ENHANCEMENT],[BUGFIX]