[jira] [Commented] (SPARK-6221) SparkSQL should support auto merging output files

["Tian Tian (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-6221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17002085#comment-17002085 ] 

Tian Tian commented on SPARK-6221:
----------------------------------

I encounterd this problem and find [issue-24940](https://issues.apache.org/jira/browse/SPARK-24940)

Use /*+ COALESCE(numPartitions) */ or /*+ REPARTITION(numPartitions) */ in spark sql query will control output file numbers.

In my parctice I recommend second parm for users, because it will generate a new stage to do this job, while first parm won't which may lead the job dead because of fewer tasks in the last stage.

> SparkSQL should support auto merging output files
> -------------------------------------------------
>
>                 Key: SPARK-6221
>                 URL: https://issues.apache.org/jira/browse/SPARK-6221
>             Project: Spark
>          Issue Type: New Feature
>          Components: SQL
>            Reporter: Tianyi Wang
>            Priority: Major
>
> Hive has a feature that could automatically merge small files in HQL's output path. 
> This feature is quite useful for some cases that people use {{insert into}} to  handle minute data from the input path to a daily table.
> In that case, if the SQL includes {{group by}} or {{join}} operation, we always set the {{reduce number}} at least 200 to avoid the possible OOM in reduce side.
> That will cause this SQL output at least 200 files at the end of the execution. So the daily table will finally contains more than 50000 files. 
> If we could provide the same feature in SparkSQL, it will extremely reduce hdfs operations and spark tasks when we run other sql on this table.



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