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From "Ben Chambers (JIRA)" <>
Subject [jira] [Commented] (BEAM-32) Consider not emitting empty ON_TIME pane unless requested
Date Wed, 03 May 2017 20:34:04 GMT


Ben Chambers commented on BEAM-32:

Emmitting an empty creates a problem for a CombineFn. Specifically, it requires an identity.
For some classes of combine Fn there is no natural identity. For example, "the smallest string
combineFn" would have "the largest string" as its identity. But we shouldn't actually instantiate
the largest string, so then the combineFn needs to have an artificial identity (such as "null")
created, and handled.

> Consider not emitting empty ON_TIME pane unless requested
> ---------------------------------------------------------
>                 Key: BEAM-32
>                 URL:
>             Project: Beam
>          Issue Type: New Feature
>          Components: beam-model, runner-core
>            Reporter: Kenneth Knowles
>            Priority: Minor
>              Labels: Triggers, Windowing, backward-incompatible
>             Fix For: First stable release
> Today, the ReduceFnRunner sets a timers and emits an empty ON_TIME pane as long as the
trigger allows it. This could be controlled in a manner analogous to the empty final pane
at window expiration (also owned by the ReduceFnRunner).

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