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https://issues.apache.org/jira/browse/BEAM-145?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15359267#comment-15359267
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ASF GitHub Bot commented on BEAM-145:
-------------------------------------

GitHub user kennknowles opened a pull request:

    https://github.com/apache/incubator-beam/pull/573

    [BEAM-145] Fix timestamps in GroupAlsoByWindowsProperties

    Be sure to do all of the following to help us incorporate your contribution
    quickly and easily:
    
     - [x] Make sure the PR title is formatted like:
       `[BEAM-<Jira issue #>] Description of pull request`
     - [x] Make sure tests pass via `mvn clean verify`. (Even better, enable
           Travis-CI on your fork and ensure the whole test matrix passes).
     - [x] Replace `<Jira issue #>` in the title with the actual Jira issue
           number, if there is one.
     - [x] If this contribution is large, please file an Apache
           [Individual Contributor License 
Agreement](https://www.apache.org/licenses/icla.txt).
    
    ---
    
    Some of the timestamps were not adjusted when 
[BEAM-145](https://issues.apache.org/jira/browse/BEAM-145) was fixed to respect 
the `WindowFn`'s timestamps.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/kennknowles/incubator-beam GABWProperties

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/incubator-beam/pull/573.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #573
    
----
commit 190740f7971be506df5416dc4dfc5714bba0c972
Author: Kenneth Knowles <k...@google.com>
Date:   2016-07-01T16:53:37Z

    Fix timestamps in GroupAlsoByWindowsProperties
    
    Some of the timestamps were not adjusted when
    BEAM-145 was fixed to respect the WindowFn's
    timestamps.

----


> OutputTimeFn#assignOutputTime overrides WindowFn#getOutputTime in unfortunate 
> ways
> ----------------------------------------------------------------------------------
>
>                 Key: BEAM-145
>                 URL: https://issues.apache.org/jira/browse/BEAM-145
>             Project: Beam
>          Issue Type: Bug
>          Components: runner-core
>            Reporter: Kenneth Knowles
>            Assignee: Kenneth Knowles
>            Priority: Minor
>              Labels: windowing
>             Fix For: 0.1.0-incubating
>
>
> Today the {{OutputTimeFn}} includes {{#assignOutputTime}}, {{#combine}}, and 
> {{#merge}}. Together these express the grouping of timestamps, analogous to 
> the grouping of values in a GBK / Combine, in a canonical way.
> The default {{OutputTimeFn}} is provided by the {{WindowFn}}. In particular, 
> {{SlidingWindows}} provides an {{OutputTimeFn}} that shifts input timestamps 
> later to avoid watermark stuckness and then takes the minimum to compute the 
> output timestamp.
> The SDK additionally provides instance for "min", "max" and "end of window" 
> output timestamps.
> Unfortunately,  if one overrides the {{OutputTimeFn}} to one of these, the 
> shifting done by {{SlidingWindows}} is lost.
> This is actually only a minor problem for now, since "min" is the default, 
> "end of window" is unaffected, and "max" has only esoteric uses.The fix is 
> easy:
> This is interrelated with another suggested change:  Since there are only 
> three common {{OutputTimeFn}} instances, and it is a high bandwidth API, it 
> does not seem worthwhile to leave it in userland. So it is proposed to reduce 
> it to an enum, which would leave only the {{WindowFn}} as a userland place 
> for timestamp adjustments. (requiring special casing for end-of-window, since 
> it cannot be implemented without owning {{#assignOutputTime}})



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