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https://issues.apache.org/jira/browse/BEAM-146?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Daniel Halperin updated BEAM-146:
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Fix Version/s: 0.2.0-incubating
> WindowFn.AssignContext leaks implementation details about compressed
> WindowedValue representation
> -------------------------------------------------------------------------------------------------
>
> Key: BEAM-146
> URL: https://issues.apache.org/jira/browse/BEAM-146
> Project: Beam
> Issue Type: Bug
> Components: beam-model
> Reporter: Kenneth Knowles
> Assignee: Kenneth Knowles
> Priority: Minor
> Fix For: 0.2.0-incubating
>
>
> Today, {{WindowFn.AssignContext}} provides simultaneous access to all of the
> windows that a value has been placed in.
> Providing access to the current window for a value is convenient for, e.g.
> converting day windows to hour windows for each hour of the assign day. But
> providing access to all the assigned windows allows spooky action across
> windows, and is generally not intended to be observable - elements are
> semantically considered to be "duplicated" into each of the assigned windows.
> This ticket proposes that the {{AssignContext}} should provide only a single
> window, and that windows should be "exploded" prior to window re-assignment
> so that elements are only observed within one window at a time. This can be
> accomplished trivially today via surgical insertion of
> {{RequiresWindowAccess}} but the {{AssignContext}} should have its API
> adjusted to be explicit about it, too.
> This will affect only pipelines for which _all_ of the following hold:
> - assigns to sliding windows (or custom {{WindowFn}} that places each
> element in multiple windows)
> - re-assigns to different windows without a {{GroupByKey}} between.
> - the new window assignment actually does depend on the full set of windows
> assigned
> I hypothesize the number of such pipelines is zero.
> I expect to address this during the Beam Runner API design.
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