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From aljoscha <...@git.apache.org>
Subject [GitHub] flink pull request #3191: [FLINK-5529] [FLINK-4752] [docs] Improve / extends...
Date Wed, 25 Jan 2017 17:32:12 GMT
Github user aljoscha commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3191#discussion_r97827894
  
    --- Diff: docs/dev/windows.md ---
    @@ -622,133 +690,138 @@ input
     </div>
     </div>
     
    -## Dealing with Late Data
    +## Triggers
     
    -When working with event-time windowing it can happen that elements arrive late, i.e the
    -watermark that Flink uses to keep track of the progress of event-time is already past
the
    -end timestamp of a window to which an element belongs. Please
    -see [event time](./event_time.html) and especially
    -[late elements](./event_time.html#late-elements) for a more thorough discussion of
    -how Flink deals with event time.
    +A `Trigger` determines when a window (as formed by the `WindowAssigner`) is ready to
be
    +processed by the *window function*. Each `WindowAssigner` comes with a default `Trigger`.

    +If the default trigger does not fit your needs, you can specify a custom trigger using
`trigger(...)`.
     
    -You can specify how a windowed transformation should deal with late elements and how
much lateness
    -is allowed. The parameter for this is called *allowed lateness*. This specifies by how
much time
    -elements can be late. Elements that arrive within the allowed lateness are still put
into windows
    -and are considered when computing window results. If elements arrive after the allowed
lateness they
    -will be dropped. Flink will also make sure that any state held by the windowing operation
is garbage
    -collected once the watermark passes the end of a window plus the allowed lateness.
    +The trigger interface provides five methods that react to different events: 
    --- End diff --
    
    I think it doesn't "provide" the methods, maybe write "The trigger interface has five
methods that allow a Trigger to react to different events"


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