[GitHub] spark pull request: [SPARK-9066][SQL] Improve cartesian performanc...

[cloud-fan <gi...@git.apache.org>]

Github user cloud-fan commented on the pull request:

    https://github.com/apache/spark/pull/7417#issuecomment-145190616
  
    @zsxwing the rdds order do matters for `RDD.cartesian`, because of the inefficient way we compute `CartesianRDD`:
    ```
    for (x <- rdd1.iterator(currSplit.s1, context);
         y <- rdd2.iterator(currSplit.s2, context)) yield (x, y)
    ```
    For `a.cartesian(b)`, when we compute partition in result RDD, logically we only need to compute the referenced partition of `a` and `b` once, but actually we comput partition of `b` many times according to the number of elements in partition of `a`.
    
    Anyway this PR LGTM


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