[jira] [Commented] (SPARK-20638) Optimize the CartesianRDD to reduce repeatedly data fetching

["Sean Owen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-20638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16002295#comment-16002295 ] 

Sean Owen commented on SPARK-20638:
-----------------------------------

I am still not clear why grouped() is better than buffering the iterator? isn't it just {{.buffered}}?

> Optimize the CartesianRDD to reduce repeatedly data fetching
> ------------------------------------------------------------
>
>                 Key: SPARK-20638
>                 URL: https://issues.apache.org/jira/browse/SPARK-20638
>             Project: Spark
>          Issue Type: Improvement
>          Components: Spark Core
>    Affects Versions: 2.2.0
>            Reporter: Teng Jiang
>
> In CartesianRDD, group each iterator to multiple groups. Thus in the second iteration, the data with be fetched (num of data)/groupSize times, rather than (num of data) times.
> The test results are:
> Test Environment : 3 workers, each has 10 cores, 30G memory, 1 executor
> Test data : users : 480,189, each is a 10-dim vector, and items : 17770, each is a 10-dim vector.
> With default CartesianRDD, cartesian time is 2420.7s.
> With this proposal, cartesian time is 45.3s
> 50x faster than the original method.



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