[
https://issues.apache.org/jira/browse/KAFKA-9611?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17046678#comment-17046678
]
Neil Green commented on KAFKA-9611:
-----------------------------------
I think it is a bug. One received message results in two messages being
published, one of which has a value which has never been correct. The number of
questions about this behaviour on SO suggests that it is, at the very best,
extremely surprising for a lot of users. When both the adder and subtractor are
executed on the same node it should be possible for them to be applied before
emitting the result.
> 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 |}}
> {{+----------+--+}}
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
