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https://issues.apache.org/jira/browse/KAFKA-3705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16254129#comment-16254129
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Trevor Huey commented on KAFKA-3705:
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[~jfilipiak] Please bear with me while I try to get caught up. I'm not yet
familiar with the Kafka code base. I have a few questions to try to figure out
how I can get involved:
1. It seems like we need to get buy-in on your KIP-213? It doesn't seem like
there's been much activity on it besides yourself in a while. What's your
current plan of attack for getting that approved?
2. I know you said that the most difficult part is yet to be done. Is there
some code you can point me toward so I can start digging in and better
understand why this is so difficult?
3. This issue has been open since May '16. How far out do you think we are from
getting this implemented? Unfortunately, it seems like there's not a lot of
momentum behind it from the Kafka team, despite this being labeled a "Major"
bug.
> Support non-key joining in KTable
> ---------------------------------
>
> Key: KAFKA-3705
> URL: https://issues.apache.org/jira/browse/KAFKA-3705
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Guozhang Wang
> Labels: api
>
> Today in Kafka Streams DSL, KTable joins are only based on keys. If users
> want to join a KTable A by key {{a}} with another KTable B by key {{b}} but
> with a "foreign key" {{a}}, and assuming they are read from two topics which
> are partitioned on {{a}} and {{b}} respectively, they need to do the
> following pattern:
> {code}
> tableB' = tableB.groupBy(/* select on field "a" */).agg(...); // now tableB'
> is partitioned on "a"
> tableA.join(tableB', joiner);
> {code}
> Even if these two tables are read from two topics which are already
> partitioned on {{a}}, users still need to do the pre-aggregation in order to
> make the two joining streams to be on the same key. This is a draw-back from
> programability and we should fix it.
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