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https://issues.apache.org/jira/browse/KAFKA-3705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15395478#comment-15395478
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Jan Filipiak edited comment on KAFKA-3705 at 7/27/16 11:24 AM:
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Something that starts happening to us is that for low cardinality columns on
the join, the prefix scan on the rocks can return a big amount of values. That
leads to to much time spent between poll() and us loosing group membership. One
could check the need for a poll() on the consumer while context.forward()
maybe, as we do context.forward() for every row that comes from the prefix
scan. The fix with setting session time-out very high, that we are currently
using is not that good IMO
was (Author: jfilipiak):
Something that starts happening to us is that for low cardinality columns on
the join, the prefix scan on the rocks can return a big amount of values. That
leads to to much time spent between poll() and us loosing group membership. One
could check the need for a poll() on the consumer while context.forward()
maybe. The fix with setting session time-out very high, that we are currently
using is not that good IMO
> 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: Liquan Pei
> Labels: api
> 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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