[jira] [Commented] (KAFKA-3705) Support non-key joining in KTable

["Michael Noll (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15826064#comment-15826064 ] 

Michael Noll commented on KAFKA-3705:
-------------------------------------

[~jfilipiak]: Now that support for global KTables is around the corner (see KIP-99 at https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=67633649), would that serve all / most of your needs here?  I am aware that "non-key joining in KTable" and "global KTables" is not a full overlap, but still the overlap is quite significant.

> 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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