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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-439) merge small files whenever possible
Date Fri, 19 Jun 2009 02:19:07 GMT

    [ https://issues.apache.org/jira/browse/HIVE-439?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12721622#action_12721622
] 

Zheng Shao commented on HIVE-439:
---------------------------------

@hive.439.3.patch:
I don't understand how the ConditionalTask gets the resolver and resolverCtx at execution
time.

Are they serialized together with the ConditionalTask?
If so, we need to mark those classes as serializable and move them to ConditionalWork, right?
Otherwise it kind of breaks the implicit contract that everything that needs to be serialized
is in the Work instead of the Task.


> 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
>         Attachments: hive.439.1.patch, hive.439.2.patch, hive.439.3.patch
>
>
> 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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