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https://issues.apache.org/jira/browse/SPARK-32104?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17146839#comment-17146839
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Zuo Dao commented on SPARK-32104:
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Yes, same problem. [~viirya]

> Avoid full outer join OOM on skewed dataset
> -------------------------------------------
>
>                 Key: SPARK-32104
>                 URL: https://issues.apache.org/jira/browse/SPARK-32104
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 2.3.1, 2.4.6, 3.0.0
>            Reporter: Zuo Dao
>            Priority: Minor
>
> SPARK-24985 changed {{SortMergeJoinExec}} to use 
> {{ExternalAppendOnlyUnsafeRowArray}} on {{SortMergeFullOuterJoinScanner}}.
> But its performance is very poor, because when matching the key, you need to 
> constantly get the element at the specified position according to the index.
> This PR add a {{FileBasedAppendOnlyUnsafeRowArray}}.
> It can quickly locate the corresponding data according to the given index 
> because of the offsets array in memory.
> And in memory buffer rows can be limited by 
> {{spark.sql.sortMergeJoinExec.buffer.in.memory.threshold}}.



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