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https://issues.apache.org/jira/browse/SPARK-25274?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16596860#comment-16596860
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Bryan Cutler commented on SPARK-25274:
--------------------------------------

This is a followup to SPARK-23030 that is now possible since Arrow stream 
format is being used

> Improve `toPandas` with Arrow by sending out-of-order record batches
> --------------------------------------------------------------------
>
>                 Key: SPARK-25274
>                 URL: https://issues.apache.org/jira/browse/SPARK-25274
>             Project: Spark
>          Issue Type: Sub-task
>          Components: PySpark, SQL
>    Affects Versions: 2.4.0
>            Reporter: Bryan Cutler
>            Priority: Major
>
> When executing {{toPandas}} with Arrow enabled, partitions that arrive in the 
> JVM out-of-order must be buffered before they can be send to Python. This 
> causes an excess of memory to be used in the driver JVM and increases the 
> time it takes to complete because data must sit in the JVM waiting for 
> preceding partitions to come in.
> This can be improved by sending out-of-order partitions to Python as soon as 
> they arrive in the JVM, followed by a list of indices so that Python can 
> assemble the data in the correct order. This way, data is not buffered at the 
> JVM and there is no waiting on particular partitions so performance will be 
> increased.



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