[jira] [Commented] (FLINK-5375) Fix watermark documentation

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-5375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15832216#comment-15832216 ] 

ASF GitHub Bot commented on FLINK-5375:
---------------------------------------

GitHub user tzulitai opened a pull request:

    https://github.com/apache/flink/pull/3185

    [FLINK-5375] [doc] Fix Watermark Semantics

    Fix watermark semantics in documenation to be correctly aligned with implementation: a Watermark _t_ declares that event time has reached time _t_ in that stream, meaning that there should be no more elements from the stream with a timestamp **t' <= t** (i.e. events with timestamps older or equal to the watermark).
    
    Also proof-read and corrected some mistakes in event-time / watermark related docs.


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/tzulitai/flink FLINK-5375

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/3185.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #3185
    
----
commit a9469b982f58a37f395fb53fc7b762b557437e4f
Author: Tzu-Li (Gordon) Tai <tz...@apache.org>
Date:   2017-01-20T18:12:27Z

    [FLINK-5375] [doc] Fix Watermark Semantics

----


> Fix watermark documentation
> ---------------------------
>
>                 Key: FLINK-5375
>                 URL: https://issues.apache.org/jira/browse/FLINK-5375
>             Project: Flink
>          Issue Type: Bug
>          Components: Documentation, Project Website
>    Affects Versions: 1.2.0, 1.1.3, 1.3.0
>            Reporter: Fabian Hueske
>            Assignee: Tzu-Li (Gordon) Tai
>            Priority: Critical
>             Fix For: 1.2.0, 1.3.0, 1.1.5
>
>
> The [documentation of watermarks|https://ci.apache.org/projects/flink/flink-docs-release-1.2/dev/event_time.html#event-time-and-watermarks] is not correct. It states 
> {quote}
> A Watermark(t) declares that event time has reached time t in that stream, meaning that all events with a timestamps t’ < t have occurred.
> {quote}
> whereas the JavaDocs which is aligned with implementation says
> {quote}
> A Watermark tells operators that receive it that no elements with a
> timestamp older or equal to the watermark timestamp should arrive at the
> operator.
> {quote}
> The documentation needs to be updated. Moreover, we need to carefully check that the watermark semantics are correctly described in other pages of the documentation and blog posts published on the Flink website.



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