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https://issues.apache.org/jira/browse/KAFKA-13769?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17680858#comment-17680858
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Matthias J. Sax commented on KAFKA-13769:
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I just updated fixed version from 3.0.0 to 3.3.3 and 3.4.0. Cf
https://issues.apache.org/jira/browse/KAFKA-14646 for details.
> KTable FK join can miss records if an upstream non-key-changing operation
> changes key serializer
> ------------------------------------------------------------------------------------------------
>
> Key: KAFKA-13769
> URL: https://issues.apache.org/jira/browse/KAFKA-13769
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Alex Sorokoumov
> Assignee: Alex Sorokoumov
> Priority: Major
> Fix For: 3.4.0, 3.3.3
>
>
> Consider a topology, where the source KTable is followed by a
> {{transformValues}} operation [that changes the key
> schema|https://github.com/apache/kafka/blob/db724f23f38cdb6c668a10681ea2a03bb11611ad/streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java#L452]
> followed by a foreign key join. The FK join might miss records in such a
> topology because they might be sent to the wrong partitions.
> As {{transformValues}} does not change the key itself, repartition won't
> happen after this operation. However, the KTable instance that calls
> {{doJoinOnForeignKey}} uses the new serde coming from {{transformValues}}
> rather than the original. As a result, all nodes in the FK join topology
> except for
> [SubscriptionResolverJoinProcessorSupplier|https://github.com/apache/kafka/blob/db724f23f38cdb6c668a10681ea2a03bb11611ad/streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java#L1225-L1232]
> use the "new" serde. {{SubscriptionResolverJoinProcessorSupplier}} uses the
> old one because it uses
> [valueGetterSupplier|https://github.com/apache/kafka/blob/db724f23f38cdb6c668a10681ea2a03bb11611ad/streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java#L1225]
> that in turn will retrieve the records from the topic.
> A different serializer might serialize keys to different series of bytes,
> which will lead to sending them to the wrong partitions. To run into that
> issue, multiple things must happen:
> * a topic should have more than one partition,
> * KTable's serializer should be modified via a non-key-changing operation,
> * the new serializer should serialize keys differently
> In practice, it might happen if the key type is a {{Struct}} because it
> serializes to a JSON string {{columnName -> value}}. If the
> {{transformValues}} operation changes column names to avoid name clashes with
> the joining table, such join can lead to incorrect behavior.
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