[jira] [Created] (SPARK-3356) Document when RDD elements' ordering within partitions is nondeterministic

["Matei Zaharia (JIRA)" <ji...@apache.org>]

Matei Zaharia created SPARK-3356:
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             Summary: Document when RDD elements' ordering within partitions is nondeterministic
                 Key: SPARK-3356
                 URL: https://issues.apache.org/jira/browse/SPARK-3356
             Project: Spark
          Issue Type: Documentation
          Components: Documentation
            Reporter: Matei Zaharia


As reported in SPARK-3098 for example, for users using zipWithIndex, zipWithUniqueId, etc, (and maybe even things like mapPartitions) it's confusing that the order of elements in each partition after a shuffle operation is nondeterministic (unless the operation was sortByKey). We should explain this in the docs for the zip and partition-wise operations.

Another subtle issue is that the order of values for each key in groupBy / join / etc can be nondeterministic -- we need to explain that too.



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