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From "Bill Bejeck (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (KAFKA-4601) Avoid duplicated repartitioning in KStream DSL
Date Wed, 14 Nov 2018 01:58:00 GMT

     [ https://issues.apache.org/jira/browse/KAFKA-4601?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Bill Bejeck resolved KAFKA-4601.
--------------------------------
    Resolution: Fixed

Marking this resolved with [https://github.com/apache/kafka/pull/5451.]

As [~guozhang] said we will address follow up work with individual tickets.

> Avoid duplicated repartitioning in KStream DSL
> ----------------------------------------------
>
>                 Key: KAFKA-4601
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4601
>             Project: Kafka
>          Issue Type: Sub-task
>          Components: streams
>            Reporter: Guozhang Wang
>            Priority: Major
>              Labels: performance
>
> Consider the following DSL:
> {code}
> Stream<String, String> source = builder.stream(Serdes.String(), Serdes.String(),
"topic1");
> Stream<String, String> mapped = source.map(..);
>         KTable<String, Long> counts = mapped
>                 .groupByKey()
>                 .count("Counts");
>         KStream<String, String> sink = mapped.leftJoin(counts, ..);
> {code}
> The resulted topology looks like this:
> {code}
> ProcessorTopology:
> 				KSTREAM-SOURCE-0000000000:
> 					topics:		[topic1]
> 					children:	[KSTREAM-MAP-0000000001]
> 				KSTREAM-MAP-0000000001:
> 					children:	[KSTREAM-FILTER-0000000004, KSTREAM-FILTER-0000000007]
> 				KSTREAM-FILTER-0000000004:
> 					children:	[KSTREAM-SINK-0000000003]
> 				KSTREAM-SINK-0000000003:
> 					topic:		X-Counts-repartition
> 				KSTREAM-FILTER-0000000007:
> 					children:	[KSTREAM-SINK-0000000006]
> 				KSTREAM-SINK-0000000006:
> 					topic:		X-KSTREAM-MAP-0000000001-repartition
> ProcessorTopology:
> 				KSTREAM-SOURCE-0000000008:
> 					topics:		[X-KSTREAM-MAP-0000000001-repartition]
> 					children:	[KSTREAM-LEFTJOIN-0000000009]
> 				KSTREAM-LEFTJOIN-0000000009:
> 					states:		[Counts]
> 				KSTREAM-SOURCE-0000000005:
> 					topics:		[X-Counts-repartition]
> 					children:	[KSTREAM-AGGREGATE-0000000002]
> 				KSTREAM-AGGREGATE-0000000002:
> 					states:		[Counts]
> {code}
> I.e. there are two repartition topics, one for the aggregate and one for the join, which
not only introduce unnecessary overheads but also mess up the processing ordering (users are
expecting each record to go through aggregation first then the join operator). And in order
to get the following simpler topology users today need to add a {{through}} operator after
{{map}} manually to enforce repartitioning.
> {code}
> Stream<String, String> source = builder.stream(Serdes.String(), Serdes.String(),
"topic1");
> Stream<String, String> repartitioned = source.map(..).through("topic2");
>         KTable<String, Long> counts = repartitioned
>                 .groupByKey()
>                 .count("Counts");
>         KStream<String, String> sink = repartitioned.leftJoin(counts, ..);
> {code}
> The resulted topology then will look like this:
> {code}
> ProcessorTopology:
> 				KSTREAM-SOURCE-0000000000:
> 					topics:		[topic1]
> 					children:	[KSTREAM-MAP-0000000001]
> 				KSTREAM-MAP-0000000001:
> 					children:	[KSTREAM-SINK-0000000002]
> 				KSTREAM-SINK-0000000002:
> 					topic:		topic 2
> ProcessorTopology:
> 				KSTREAM-SOURCE-0000000003:
> 					topics:		[topic 2]
> 					children:	[KSTREAM-AGGREGATE-0000000004, KSTREAM-LEFTJOIN-0000000005]
> 				KSTREAM-AGGREGATE-0000000004:
> 					states:		[Counts]
> 				KSTREAM-LEFTJOIN-0000000005:
> 					states:		[Counts]
> {code} 
> This kind of optimization should be automatic in Streams, which we can consider doing
when extending from one-operator-at-a-time translation.



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