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Date: Mon, 22 Aug 2016 01:34:20 +0000 (UTC)
From: "Daniel Halperin (JIRA)" <jira@apache.org>
To: commits@beam.incubator.apache.org
Message-ID: <JIRA.12952913.1458754702000.365453.1471829660465@Atlassian.JIRA>
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Subject: [jira] [Updated] (BEAM-145) OutputTimeFn#assignOutputTime overrides
 WindowFn#getOutputTime in unfortunate ways
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archived-at: Mon, 22 Aug 2016 01:34:26 -0000


     [ https://issues.apache.org/jira/browse/BEAM-145?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Daniel Halperin updated BEAM-145:
---------------------------------
    Fix Version/s:     (was: 0.1.0-incubating)

> 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
>
> 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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