[jira] [Commented] (KAFKA-6687) Allow to read a topic multiple times

["Richard Yu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-6687?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16530668#comment-16530668 ] 

Richard Yu commented on KAFKA-6687:
-----------------------------------

It appears that the summary and the description is somewhat contradictory: while the summary states that we should "allow a topic to be read multiple times", in the description it states that "we should allow adding a topic multiple times and rewrite the topology internally so that it can be read *only* once." Which one is it?

> Allow to read a topic multiple times
> ------------------------------------
>
>                 Key: KAFKA-6687
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6687
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Matthias J. Sax
>            Priority: Major
>
> Users often want to read topic multiple times. However, this is not possible because there is a single consumer and thus a topic can only be consumed once.
> Users get an exception
> {quote}Exception in thread “main” org.apache.kafka.streams.errors.TopologyException: Invalid topology: Topic source has already been registered by another source.
> {quote}
> If they use a topic name in multiple `stream()`, `table()`, `globalTable()` calls.
> However, with KAFKA-6034 in place, we could allow adding a topic multiple times and rewrite the topology internally to only read the topic once. This would simplify application code as users don't need to put workaround in place to get the same behavior.



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