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https://issues.apache.org/jira/browse/HIVE-8043?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14138824#comment-14138824
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Rui Li commented on HIVE-8043:
------------------------------
Hi [~xuefuz],
The DDL task that merges files is an alter table statement:
{code}
ALTER TABLE tbl CONCATENATE;
{code}
In this case, the DDL task creates a {{MergeFileTask}} and {{MergeFileTask}}
launches an MR job to merge the files. This feature currently only supports
RC/Orc tables.
Strange thing is that I didn't find anything about this in the wiki or other
official doc. Maybe I'm missing something?
The main problem I see here is that, ideally we should launch the job according
to the execution engine. But DDL task uses a different semantic analyzer
{{DDLSemanticAnalyzer}}, and always launches an MR job. I think Tez doesn't
handle this either.
> Support merging small files [Spark Branch]
> ------------------------------------------
>
> Key: HIVE-8043
> URL: https://issues.apache.org/jira/browse/HIVE-8043
> Project: Hive
> Issue Type: Task
> Components: Spark
> Reporter: Xuefu Zhang
> Assignee: Rui Li
> Labels: Spark-M1
> Attachments: HIVE-8043.1-spark.patch
>
>
> Hive currently supports merging small files with MR as the execution engine.
> There are options available for this, such as
> {code}
> hive.merge.mapfiles
> hive.merge.mapredfiles
> {code}
> Hive.merge.sparkfiles is already introduced in HIVE-7810. To make it work, we
> might need a little more research and design on this.
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