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

["Guozhang Wang (JIRA)" <ji...@apache.org>]

Guozhang Wang created KAFKA-3705:
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             Summary: 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
            Assignee: Guozhang Wang
             Fix For: 0.10.1.0


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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