[GitHub] spark pull request #16294: [SPARK-18669][SS][DOCS] Update Apache docs for St...

[wangmiao1981 <gi...@git.apache.org>]

Github user wangmiao1981 commented on a diff in the pull request:

    https://github.com/apache/spark/pull/16294#discussion_r92757455
  
    --- Diff: docs/structured-streaming-programming-guide.md ---
    @@ -671,12 +678,114 @@ windowedCounts = words.groupBy(
     </div>
     
     
    +### Handling Late Data and Watermarking
     Now consider what happens if one of the events arrives late to the application.
     For example, a word that was generated at 12:04 but it was received at 12:11. 
    -Since this windowing is based on the time in the data, the time 12:04 should be considered for windowing. This occurs naturally in our window-based grouping \u2013 the late data is automatically placed in the proper windows and the correct aggregates are updated as illustrated below.
    +Since this windowing is based on the time in the data, the time 12:04 should be considered for 
    +windowing. This occurs naturally in our window-based grouping \u2013 the late data is 
    +automatically placed in the proper windows and the correct aggregates are updated as illustrated below.
     
     ![Handling Late Data](img/structured-streaming-late-data.png)
     
    +Furthermore, since Spark 2.1, you can define a watermark on the event time, and specify the threshold 
    +on how late the date can be in terms of the event time. The engine will automatically track the 
    +event time and drop any state that is related to old windows that are not expected to receive older 
    +than (max event time seen - late threshold). This allows the engine to bound the size of the state 
    +that is needed for calculating windowed aggregates. For example, we can apply watermarking to the 
    +previous example as follows.
    +
    +<div class="codetabs">
    +<div data-lang="scala"  markdown="1">
    +
    +{% highlight scala %}
    +import spark.implicits._
    --- End diff --
    
    Just curious, will there be a complete example in the examples folder? In documents like ML, SQL, the code is cited from the example file instead of hard code in the document. Thanks!


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