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https://issues.apache.org/jira/browse/BEAM-2680?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eugene Kirpichov updated BEAM-2680:
-----------------------------------
Description:
[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.
was:
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 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.
> 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
> Assignee: Eugene Kirpichov
> Priority: Major
>
> [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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