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From "ZhuGuanyin (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1254) job.xml should add crc check in tasktracker and sub jvm.
Date Fri, 04 Dec 2009 09:41:20 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1254?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12785838#action_12785838
] 

ZhuGuanyin commented on MAPREDUCE-1254:
---------------------------------------

Because the local inexpensive disks are not reliable, and we once found the non zero file
became zero length, but the os kernel message has no warning, while some minutes later, the
kernel message report the disk failtures. Durining that time,  the read operation return success
without throw any IOException. 

In current implementation, it would throw IOException if the job.xml missing, but it couldn't
detect the configuration file has corrupted or has being truncated.

> job.xml should add crc check in tasktracker and sub jvm.
> --------------------------------------------------------
>
>                 Key: MAPREDUCE-1254
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1254
>             Project: Hadoop Map/Reduce
>          Issue Type: New Feature
>          Components: task, tasktracker
>    Affects Versions: 0.22.0
>            Reporter: ZhuGuanyin
>
> Currently job.xml in tasktracker and subjvm are write to local disk through ChecksumFilesystem,
and already had crc checksum information, but load the job.xml file without crc check. It
would cause the mapred job finished successful but with wrong data because of disk error.
 Example: The tasktracker and sub task jvm would load the default configuration if it doesn't
successfully load the job.xml which maybe replace the mapper with IdentityMapper. 

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