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https://issues.apache.org/jira/browse/SPARK-26858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16772570#comment-16772570
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Hyukjin Kwon commented on SPARK-26858:
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Yes .. that's matched with what I was thinking. Thanks for clarification. T
he discussion is getting long .. to make it short ..
- Arrow requires to know its schema for its output
- Schema can be only known after R native function execution for its output
- It might be able to work around by, for instance, set the DataFrame's
output as {{binary}} type for its output, and then construct Arrow streaming
format by, somehow, lazily providing the schema (for its batch or {{Schema}}).
Given my try, it's quite hacky since it basically means you need to send
{{Schema}} from executor to driver (to be used in {{collect()}} later).
Yes, it's currently se/deserialized row by row bytes over socket.
> Vectorized gapplyCollect, Arrow optimization in native R function execution
> ---------------------------------------------------------------------------
>
> Key: SPARK-26858
> URL: https://issues.apache.org/jira/browse/SPARK-26858
> Project: Spark
> Issue Type: Sub-task
> Components: SparkR, SQL
> Affects Versions: 3.0.0
> Reporter: Hyukjin Kwon
> Assignee: Hyukjin Kwon
> Priority: Major
>
> Unlike gapply, gapplyCollect requires additional ser/de steps because it can
> omit the schema, and Spark SQL doesn't know the return type before actually
> execution happens.
> In original code path, it's done via using binary schema. Once gapply is done
> (SPARK-26761). we can mimic this approach in vectorized gapply to support
> gapplyCollect.
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