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https://issues.apache.org/jira/browse/KAFKA-10493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17433123#comment-17433123
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Matthias J. Sax commented on KAFKA-10493:
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A custom timestamp extractor seems orthogonal. – Even if by default the
producer would set the timestamp on the record (and thus guaranteeing order),
it is also possible that the user set the timestamp explicitly via `new
ProducerRecord(...)`. Thus, even with the default timestamp extractor and
single write, users could "mess" with the timestamp order. Thus, the single
writer principle actually implies, that the user ensures that the records are
in timestamp order, independent if the timestamp is store in the record
ts-field or in the payload...
> KTable out-of-order updates are not being ignored
> -------------------------------------------------
>
> Key: KAFKA-10493
> URL: https://issues.apache.org/jira/browse/KAFKA-10493
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.6.0
> Reporter: Pedro Gontijo
> Assignee: Matthias J. Sax
> Priority: Blocker
> Fix For: 4.0.0
>
> Attachments: KTableOutOfOrderBug.java, out-of-order-table.png
>
>
> On a materialized KTable, out-of-order records for a given key (records which
> timestamp are older than the current value in store) are not being ignored
> but used to update the local store value and also being forwarded.
> I believe the bug is here:
> [https://github.com/apache/kafka/blob/2.6.0/streams/src/main/java/org/apache/kafka/streams/state/internals/ValueAndTimestampSerializer.java#L77]
> It should return true, not false (see javadoc)
> The bug impacts here:
> [https://github.com/apache/kafka/blob/2.6.0/streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableSource.java#L142-L148]
> I have attached a simple stream app that shows the issue happening.
> Thank you!
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