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Date: Tue, 7 Jun 2011 00:54:58 +0000 (UTC)
From: "Namit Jain (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
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Subject: [jira] [Created] (HIVE-2201) remove name node calls in hive by
 creating temporary directories
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remove name node calls in hive by creating temporary directories
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                 Key: HIVE-2201
                 URL: https://issues.apache.org/jira/browse/HIVE-2201
             Project: Hive
          Issue Type: Improvement
            Reporter: Namit Jain


Currently, in Hive, when a file gets written by a FileSinkOperator,
the sequence of operations is as follows:

1. In tmp directory tmp1, create a tmp file _tmp_1
2. At the end of the operator, move
/tmp1/_tmp_1 to /tmp1/1
3. Move directory /tmp1 to /tmp2
4. For all files in /tmp2, remove all files starting with _tmp and
duplicate files.

Due to speculative execution, a lot of temporary files are created
in /tmp1 (or /tmp2). This leads to a lot of name node calls,
specially for large queries.

The protocol above can be modified slightly:

1. In tmp directory tmp1, create a tmp file _tmp_1
2. At the end of the operator, move
/tmp1/_tmp_1 to /tmp2/1
3. Move directory /tmp2 to /tmp3
4. For all files in /tmp3, remove all duplicate files.

This should reduce the number of tmp files.

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