fix(tdigest): fix centroid encoding overwrite for same mean #2878
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LindaSummer
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Sorry for delaying, I'm quite busy this week, will take a round tonight |
mapleFU
approved these changes
Apr 15, 2025
| PutDouble(&sub_key, centroid.mean); // It uses EncodeDoubleToUInt64 and keeps original order of double | ||
| // The tdigest centroids only cares about the weight rather than the mean, so different centroids may have same mean, | ||
| // we should keep them with same original order, this seq id could be discarded in decode | ||
| PutFixed32(&sub_key, seq); |
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Hi @mapleFU ,
Thanks very much for your kind review!😊
I thought about the size when adding this seq-id.
The compression is uint32 now, so the limitation of centroids is uint32 maximum.
So I decided to use uint32 for safety.
Best Regards,
Edward
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PragmaTwice
approved these changes
Apr 16, 2025
PragmaTwice
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Issue
TDigest only cares about weight when merging, so it is possible to have centroids with same mean.
This will lead the centroids overwriting during serialization.
Proposed Changes
Add a seq id to make centroids mean encoding keep same order as the original centroids list without confliction.
Related Issue
#2849