[BEAM-34] Change default output timestamp for combined values to end of window

• Type: Improvement
• Status: Resolved
• Priority: P2
• Resolution: Fixed
• Fix Version/s: 0.1.0-incubating
• Component/s: beam-model
• Labels: Windowing backward-incompatible
• Assignee: Kenneth Knowles
• Reporter: Kenneth Knowles
• Created: 19/Feb/16 22:37
• Updated: 24/Jul/20 20:56
• Resolved: 09/May/16 18:39

Description

Today, the output timestamp for a combined value (including iterables output by GroupByKey) is the earliest non-late timestamp of any element combined together. The user can customize this by specifying an OutputTimeFn, for example choosing the latest non-late timestamp, or the end of the window.

In many respects, the end of the window is the best behaved as a default, and is very easy to make performant. We have deferred making this change for backwards compatibility; this is a good time to do so.