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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