[jira] [Closed] (SPARK-6974) Possible error in TwitterPopularTags

["Nicola Ferraro (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-6974?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Nicola Ferraro closed SPARK-6974.
---------------------------------

Not an issue

> Possible error in TwitterPopularTags
> ------------------------------------
>
>                 Key: SPARK-6974
>                 URL: https://issues.apache.org/jira/browse/SPARK-6974
>             Project: Spark
>          Issue Type: Bug
>            Reporter: Nicola Ferraro
>            Priority: Minor
>
> Looking at the example for Twitter popular tags in spark streaming (https://github.com/apache/spark/blob/master/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterPopularTags.scala), it seems that the algorithm can have issues in some cases.
> Top k tags are computed using the following function on a DStream:
> topCounts60.foreachRDD(rdd => { ... print ... })
> But the function passed to "foreachRDD" is called multiple times when your DStream is composed of multiple RDDs, once per RDD in the DStream, resulting in multiple Top-k charts.
> Probably this scenario is unlikely to happen, because a previous transformation on the DStream (reduceByKeyAndWindow) collapses all RDDs of the stream into a single one.
> The problem is that this behavior is not stated in the documentation and can be changed in future versions.
> Moreover, computing correctly the topK chart in streaming seems impossible if you rely on the documentation only. But it is the base algorithm for many RT dashboard use cases.
> I have also tried to get some reply on stackoverflow (http://stackoverflow.com/questions/29539655/how-to-compute-the-top-k-words).



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