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https://issues.apache.org/jira/browse/BEAM-1396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15853298#comment-15853298
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Daniel Halperin edited comment on BEAM-1396 at 2/5/17 5:54 PM:
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To add a little more flavor: I'm not sure what right thing to do with unused or
little-used code in {{runners-core}}. These are meant to be illustrative and/or
useful to show runners how key functionality can be implemented. So, among many
courses of action:
1. More clearly document expectations in
{{GroupAlsoByWindowsViaOutputBufferDoFn}}
2. Possibly add another version ({{GroupAlsoByWindowsUsingSortedInputDoFn}} or
a flag that indicates whether input is already sorted. (ViaSortedOutputBuffer)?
3. .....
was (Author: dhalp...@google.com):
To add a little more flavor: I'm not sure what right thing to do with unused or
little-used code in {{runners-core}}. These are meant to be illustrative and/or
useful to show runners how key functionality can be implemented. So, among many
courses of action:
1. More clearly document expectations in
{{GroupAlsoByWindowsViaOutputBufferDoFn}}
1. Possibly add another version ({{GroupAlsoByWindowsUsingSortedInputDoFn}} or
a flag that indicates whether input is already sorted. (ViaSortedOutputBuffer)?
1 .....
> GABWVOBDoFn expects grouped values to be ordered by their timestamp but there
> is no such guarantee
> --------------------------------------------------------------------------------------------------
>
> Key: BEAM-1396
> URL: https://issues.apache.org/jira/browse/BEAM-1396
> Project: Beam
> Issue Type: Bug
> Components: sdk-java-core
> Reporter: Amit Sela
> Assignee: Kenneth Knowles
>
> GABWVOBDoFn relies on the grouped values to be ordered by their timestamp but
> nothing in the SDK guarantees this:
> https://github.com/apache/beam/blob/master/runners/core-java/src/main/java/org/apache/beam/runners/core/GroupAlsoByWindowsViaOutputBufferDoFn.java#L86
> If such a chunk of timestamped values will be processed out-of-order I assume
> we'd end up with an {{IllegalStateException}} thrown here:
> https://github.com/apache/beam/blob/master/runners/core-java/src/main/java/org/apache/beam/runners/core/InMemoryTimerInternals.java#L191
> I suggest we go ahead and add sorting before processing the bundle in chunks
> - this might prove expensive in extreme cases where a very large bundle with
> very few keys is processed, but it seems that timestamp order is necessary.
> As for runners who provide order guarantee, since GABW is optional I don't
> see an issue here, though [~dhalp...@google.com] suggested we add a
> "shouldSort" flag.
> Also, probably worth creating a test for this, though it would prove
> difficult since we would have to preset the order which is the problem to
> begin with :-)
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