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From "Kenneth Knowles (JIRA)" <>
Subject [jira] [Resolved] (BEAM-170) Session windows should not be identified by their bounds
Date Fri, 01 Dec 2017 17:46:00 GMT


Kenneth Knowles resolved BEAM-170.
       Resolution: Invalid
         Assignee: Kenneth Knowles
    Fix Version/s: Not applicable

> Session windows should not be identified by their bounds
> --------------------------------------------------------
>                 Key: BEAM-170
>                 URL:
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-java-core
>            Reporter: Kenneth Knowles
>            Assignee: Kenneth Knowles
>              Labels: backward-incompatible
>             Fix For: Not applicable
> Today, if two session windows for the same key have the same bounds, they are considered
the same window. This is an accident. It is not intended that any session windows are considered
equal except via the operation of merging them into the same session.
> A risk associated with this behavior is that two windows that happen to coincide will
share per-window-and-key state rather than evolving separately and having their separate state
reconciled by state merging logic. These code paths are not required to be coherent, and in
practice they are not.
> In particular, if the trigger for a session window ever finishes, then subsequent data
in a window with the same bounds will be dropped, whereas if it had differed by a millisecond
it would have created a new session, ignoring the previously closed session.

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