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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Created] (YARN-202) Log Aggregation generates a storm of fsync() for namenode
Date Tue, 06 Nov 2012 00:30:12 GMT
Kihwal Lee created YARN-202:
-------------------------------

             Summary: Log Aggregation generates a storm of fsync() for namenode
                 Key: YARN-202
                 URL: https://issues.apache.org/jira/browse/YARN-202
             Project: Hadoop YARN
          Issue Type: Bug
    Affects Versions: 0.23.4, 2.0.2-alpha
            Reporter: Kihwal Lee
            Priority: Critical


When the log aggregation is on, write to each aggregated container log causes hflush() to
be called. For large clusters, this can creates a lot of fsync() calls for namenode. 

We have seen 6-7x increase in the average number of fsync operations compared to 1.0.x on
a large busy cluster. Over 99% of fsync ops were for log aggregation writing to tmp files.

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