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Posted to commits@beam.apache.org by "Kenneth Knowles (JIRA)" <ji...@apache.org> on 2016/05/09 18:40:12 UTC
[jira] [Resolved] (BEAM-145) OutputTimeFn#assignOutputTime
overrides WindowFn#getOutputTime in unfortunate ways
[ https://issues.apache.org/jira/browse/BEAM-145?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Kenneth Knowles resolved BEAM-145.
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Resolution: Fixed
> 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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