[jira] [Commented] (BEAM-2680) Improve scalability of the Watch transform

["Beam JIRA Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-2680?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17189464#comment-17189464 ] 

Beam JIRA Bot commented on BEAM-2680:
-------------------------------------

This issue was marked "stale-P2" and has not received a public comment in 14 days. It is now automatically moved to P3. If you are still affected by it, you can comment and move it back to P2.

> Improve scalability of the Watch transform
> ------------------------------------------
>
>                 Key: BEAM-2680
>                 URL: https://issues.apache.org/jira/browse/BEAM-2680
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-java-core
>            Reporter: Eugene Kirpichov
>            Priority: P3
>
> [https://github.com/apache/beam/pull/3565] introduces the Watch transform [http://s.apache.org/beam-watch-transform].
> The implementation leaves several scalability-related TODOs:
>  1) The state stores hashes and timestamps of outputs that have already been output and should be omitted from future polls. We could garbage-collect this state, e.g. dropping elements from "completed" and from addNewAsPending() if their timestamp is more than X behind the watermark.
>  2) When a poll returns a huge number of elements, we don't necessarily have to add all of them into state.pending - instead we could add only N oldest elements and ignore others, relying on future poll rounds to provide them, in order to avoid blowing up the state. Combined with garbage collection of GrowthState.completed, this would make the transform scalable to very large poll results.



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