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Posted to jira@kafka.apache.org by "Michael Noll (JIRA)" <ji...@apache.org> on 2018/11/07 15:23:00 UTC
[jira] [Commented] (KAFKA-4601) Avoid duplicated repartitioning in
KStream DSL
[ https://issues.apache.org/jira/browse/KAFKA-4601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16678379#comment-16678379 ]
Michael Noll commented on KAFKA-4601:
-------------------------------------
[~bbejeck]: With the recent topology optimization (merging of repartitioning topics) that will be available in Kafka 2.1, what's the status of this ticket?
> 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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