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https://issues.apache.org/jira/browse/KAFKA-9611?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17045775#comment-17045775
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Bruno Cadonna commented on KAFKA-9611:
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[~neilgreen] Thank you for the bug report!
When you say "Then the output should contain", is this the output that you see?
Actually, it is not true that the sum of the signal is never 4. If the update
{{abc1234/signal2 | 4}} is sent to the aggregation processor before update
{{abc1234/signal1 | 2}}, the sum is 4 before it becomes 6. It depends on your
cache size specified by {{cache.max.bytes.buffering}}, how many updates you see
downstreams. If you set {{cache.max.bytes.buffering}} to zero, you should see
all updates.
> KGroupedTable.aggregate(...) emits incorrect values
> ---------------------------------------------------
>
> Key: KAFKA-9611
> URL: https://issues.apache.org/jira/browse/KAFKA-9611
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.4.0
> Reporter: Neil Green
> Priority: Major
>
> I've run into what appears to be undesirable behaviour in a streams app.
> I have a KTable produced from a topic. The table contains entries like
> "abc1234/signal1" : 1, "abc1234/signal2" : 3
> The key is "id/signal name" and the value is an int. I want to produce a
> aggregate ktable containing the sum all of the
> signals for a given id.
> {{So if source ktable contains:}}
> {{+------------------+--+}}
> {{| abc1234/signal1 | 2 |}}
> {{| abc1234/signal2 | 4 |}}
> {{| abc4566/signal1 | 3 |}}
> {{+------------------+--+}}
> {{Then the output should contain}}
> {{+----------+--+}}
> {{| abc1234 | 6 |}}
> {{| abc4566 | 3 |}}
> {{+----------+--+}}
> {{On a change}}
> {{+------------------+--+}}
> {{| abc1234/signal1 | 3 |}}
> {{+------------------+--+}}
> {{```}}
> {{I would expect the change}}
> {{```}}
> {{+----------+--+}}
> {{| abc1234 | 7 |}}
> {{+----------+--+}}
> {{to be published.}}
> In fact there are two changelog entries published
> {{+----------+--+}}
> {{| abc1234 | 4 | // This is incorrect. The sum of the signals is never 4.}}
> {{+----------+--+}}
> Then
> {{+----------+--+}}
> {{| abc1234 | 7 |}}
> {{+----------+--+}}
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