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Posted to jira@kafka.apache.org by "Matthias J. Sax (JIRA)" <ji...@apache.org> on 2018/11/28 06:27:00 UTC
[jira] [Updated] (KAFKA-3705) Support non-key joining in KTable
[ https://issues.apache.org/jira/browse/KAFKA-3705?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Matthias J. Sax updated KAFKA-3705:
-----------------------------------
Issue Type: New Feature (was: Bug)
> Support non-key joining in KTable
> ---------------------------------
>
> Key: KAFKA-3705
> URL: https://issues.apache.org/jira/browse/KAFKA-3705
> Project: Kafka
> Issue Type: New Feature
> Components: streams
> Reporter: Guozhang Wang
> Priority: Major
> 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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