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https://issues.apache.org/jira/browse/KAFKA-20358?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matthias J. Sax resolved KAFKA-20358.
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Resolution: Duplicate
> Allow KTable/KStream and GlobalKTable on same topic
> ---------------------------------------------------
>
> Key: KAFKA-20358
> URL: https://issues.apache.org/jira/browse/KAFKA-20358
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 4.2.0
> Reporter: Stef Noten
> Priority: Minor
>
> In a single streams app, we sometimes want to consume a topic in two ways:
> # as a GlobalKTable: for global read-only reference data
> # as a KTable or KStream: to react on changes on that same topic
> Kafka Streams currently prevents this by a validation check (in
> InternalTopologyBuilder.validateTopicNotAlreadyRegistered):
> {code:java}
> var builder = new StreamsBuilder();
> builder.table("input", Consumed.as("input-as-table"));
> builder.globalTable("input", Consumed.as("input-as-globaltable"));
> builder.build(); {code}
> Result:
> {code:java}
> Topic input has already been registered by another source. {code}
>
> However, there is nothing that conceptually prevents this from working, since
> GlobalKTables do not participate in the app's consumer group and are handled
> by a dedicated consumer/subtopology/GlobalStreamThread which does not need to
> commit any offsets. So it's only the validation rule that blocks this,
> requiring an annoying workaround to mirror the topic to another one with a
> different name:
> {code:java}
> var myTable = builder.table("my-topic");
> myTable.toStream().to("my-topic-global-copy");
> var myGlobalTable = builder.globalTable("my-topic-global-copy");{code}
>
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