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[ https://issues.apache.org/jira/browse/HADOOP-4927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12658909#action_12658909 ]

Koji Noguchi commented on HADOOP-4927:
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On one of our clusters, counted number of empty "part-" files.

Out of 30 million files/dirs, 4.5 million part- files were empty. 40 users having more than 10,000 empty files.

bq. If you specify N output partitions then you should generate N output files,
I believe some users did mention that the feature of having exactly N output files is useful.

If we could somehow make the no-empty-part-files feature configurable, it'll ease up our support work a lot.
(Instead of asking our users to implement a custom outputformat, I can just ask them to set the jobconf.)


Part files on the output filesystem are created irrespective of whether the corresponding task has anything to write there
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Key: HADOOP-4927
URL: https://issues.apache.org/jira/browse/HADOOP-4927
Project: Hadoop Core
Issue Type: Bug
Reporter: Devaraj Das
Fix For: 0.20.0


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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