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https://issues.apache.org/jira/browse/BEAM-11632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17276675#comment-17276675
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Ahmet Altay commented on BEAM-11632:
------------------------------------

We can also add a similar warning to the related javadoc here 
(https://beam.apache.org/releases/javadoc/2.27.0/org/apache/beam/sdk/io/gcp/pubsub/PubsubIO.Read.html#fromTopic-java.lang.String-)

> Guardrails around fromTopic (pubsub)
> ------------------------------------
>
>                 Key: BEAM-11632
>                 URL: https://issues.apache.org/jira/browse/BEAM-11632
>             Project: Beam
>          Issue Type: Bug
>          Components: io-java-gcp, io-py-gcp
>            Reporter: Ahmet Altay
>            Assignee: Chamikara Madhusanka Jayalath
>            Priority: P2
>
> Fundamentally, we should strongly discourage the use of ephemeral topics 
> (fromTopic() in PubsubIO) in favor of user-created subscriptions. Currently, 
> the documentation for fromTopic states this matter-of-factly, without drawing 
> attention to the fact that this is almost certainly *not* what the wants:
> {quote}The Beam runner will start reading data published on this topic from 
> the time the pipeline is started. Any data published on the topic before the 
> pipeline is started will not be read by the runner.{quote}
> Suggestion: We should include an execution warning whenever fromTopic is 
> used, as well as update the documentation.



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