[jira] [Commented] (SPARK-3461) Support external groupByKey using repartitionAndSortWithinPartitions

["Patrick Wendell (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-3461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14205520#comment-14205520 ] 

Patrick Wendell commented on SPARK-3461:
----------------------------------------

I think [~sandyr] wanted to take a crack a this so I'm assigning to him.

> Support external groupByKey using repartitionAndSortWithinPartitions
> --------------------------------------------------------------------
>
>                 Key: SPARK-3461
>                 URL: https://issues.apache.org/jira/browse/SPARK-3461
>             Project: Spark
>          Issue Type: Bug
>          Components: Spark Core
>            Reporter: Patrick Wendell
>            Assignee: Sandy Ryza
>            Priority: Critical
>
> Given that we have SPARK-2978, it seems like we could support an external group by operator pretty easily. We'd just have to wrap the existing iterator exposed by SPARK-2978 with a lookahead iterator that detects the group boundaries. Also, we'd have to override the cache() operator to cache the parent RDD so that if this object is cached it doesn't wind through the iterator.
> I haven't totally followed all the sort-shuffle internals, but just given the stated semantics of SPARK-2978 it seems like this would be possible.
> It would be really nice to externalize this because many beginner users write jobs in terms of groupByKey.



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