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From "Yi Tian (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-6221) SparkSQL should support auto merging output files
Date Tue, 10 Mar 2015 02:44:38 GMT

    [ https://issues.apache.org/jira/browse/SPARK-6221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14354166#comment-14354166
] 

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

[~srowen], thanks for your comment.
I think we should add an extra job after the job generated by SQL to implement the merge operation,
just like HIVE does.
There are two benefits:
1. It will make the merge logic more independent.
2. It will be easy to merge all the output files with same size, which is good for the next
operation.

BTW, I agreed with your idea of making this argument for any output from Spark.

> 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: Yi Tian
>
> 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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