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Date: Wed, 4 Feb 2009 10:05:59 -0800 (PST)
From: "Doug Cutting (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-4927) Part files on the output filesystem
 are created irrespective of whether the corresponding task has anything to
 write there
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    [ https://issues.apache.org/jira/browse/HADOOP-4927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12670392#action_12670392 ] 

Doug Cutting commented on HADOOP-4927:
--------------------------------------

> LazyOutputFormat.set(actualoutputformat.class) and
> job.setOutputFormat(LazyOutputFormat.class)

Right.  That's the two-line penalty of a wrapper.  If we built it into FileInputFormat then it would only take one line:

FileOutputFormat.setLazyOutput(true);

but it would then also only work for subclasses of FileOutputFormat, rather than any OutputFormat implementation.  This is a tough call, since most, but not all, OutputFormats do subclass FileOutputFormat.  I'm leaning towards the wrapper, since, while a bit more complex for users, it is a cleaner layering, making FileOutputFormat less of a kitchen-sink of features.


> Part files on the output filesystem are created irrespective of whether the corresponding task has anything to write there
> --------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4927
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4927
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>            Reporter: Devaraj Das
>            Assignee: Jothi Padmanabhan
>             Fix For: 0.21.0
>
>         Attachments: hadoop-4927-v1.patch, hadoop-4927-v2.patch, hadoop-4927.patch
>
>
> When OutputFormat.getRecordWriter is invoked, a part file is created on the output filesystem. But the created RecordWriter is not used until the OutputCollector.collect call is made by the task (user's code). This results in empty part files even if the OutputCollector.collect is never invoked by the corresponding tasks.

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