[jira] [Resolved] (BEAM-170) Session windows should not be identified by their bounds

["Kenneth Knowles (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/BEAM-170?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

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: https://issues.apache.org/jira/browse/BEAM-170
>             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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