[jira] Commented: (HIVE-439) merge small files whenever possible

["Namit Jain (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-439?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12717820#action_12717820 ] 

Namit Jain commented on HIVE-439:
---------------------------------

Instead of having a map-only job to do the concatenation, I think we should use a map-reduce job.
This way, when sorting properties of a table are maintained in the metastore, they can be preserved.

> merge small files whenever possible
> -----------------------------------
>
>                 Key: HIVE-439
>                 URL: https://issues.apache.org/jira/browse/HIVE-439
>             Project: Hadoop Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Namit Jain
>
> There are cases when the input to a Hive job are thousands of small files. In this case, there is a mapper for each file. Most of the overhead for spawning all these mappers can be avoided if these small files are combined into fewer larger files.
> The problem can also be addressed by having a mapper span multiple blocks as in:
> https://issues.apache.org/jira/browse/HIVE-74
> Bit, it also makes sense in HIVE to merge files whenever possible.

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