Sophie Blee-Goldman created KAFKA-9923:
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Summary: Join window store duplicates can be compacted in
changelog
Key: KAFKA-9923
URL: https://issues.apache.org/jira/browse/KAFKA-9923
Project: Kafka
Issue Type: Bug
Components: streams
Reporter: Sophie Blee-Goldman
Stream-stream joins use the regular `WindowStore` implementation but with
`retainDuplicates` set to true. To allow for duplicates while using the same
unique-key underlying stores we just wrap the key with an incrementing sequence
number before inserting it.
This wrapping occurs at the innermost layer of the store hierarchy, which means
the duplicates must first pass through the changelogging layer. At this point
the keys are still identical. So, we end up sending the records to the
changelog without distinct keys and therefore may lose the older of the
duplicates during compaction.
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