[jira] [Commented] (SPARK-27025) Speed up toLocalIterator

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

    [ https://issues.apache.org/jira/browse/SPARK-27025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16782051#comment-16782051 ] 

Sean Owen commented on SPARK-27025:
-----------------------------------

If you fetched it all at once proactively, you have another problem: what if it doesn't fit on the driver? the use case for toLocalIterator() is probably exactly to avoid this.

> Speed up toLocalIterator
> ------------------------
>
>                 Key: SPARK-27025
>                 URL: https://issues.apache.org/jira/browse/SPARK-27025
>             Project: Spark
>          Issue Type: Wish
>          Components: Spark Core
>    Affects Versions: 2.3.3
>            Reporter: Erik van Oosten
>            Priority: Major
>
> Method {{toLocalIterator}} fetches the partitions to the driver one by one. However, as far as I can see, any required computation for the yet-to-be-fetched-partitions is not kicked off until it is fetched. Effectively only one partition is being computed at the same time. 
> Desired behavior: immediately start calculation of all partitions while retaining the download-a-partition at a time behavior.



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