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From "Amar Kamat (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4209) The TaskAttemptID should not have the JobTracker start time
Date Fri, 19 Sep 2008 04:40:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4209?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12632508#action_12632508
] 

Amar Kamat commented on HADOOP-4209:
------------------------------------

Owen,
The timestamp is introduced for a different purpose. Consider a case where the JT runs for
the first time and schedules an attempt from a tip tip_0. Let the attempt be attempt_0_0.
Let assume that the jobtracker crashes while attempt_0_0 is still running. Upon restart, the
JT might not have seen the attempt as its not logged to the history and so will go ahead and
schedule another attempt from tip_0. Now this attempt will also have the same id as the earlier
attempt (before restart) and hence the side-effect files will now clash. Consider a case where
the attempt_0_0 is done but not logged. In such a case the same tracker can now ask for an
attempt from tip_0 and might get attempt_0_0. Now not only the side effect files but also
the local directories will clash. To avoid such issues we have kept the attempt id unique
across restarts. This timestamp is redundant only if the jobtracker never restarts.

> The TaskAttemptID should not have the JobTracker start time
> -----------------------------------------------------------
>
>                 Key: HADOOP-4209
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4209
>             Project: Hadoop Core
>          Issue Type: Bug
>            Reporter: Owen O'Malley
>            Priority: Blocker
>             Fix For: 0.19.0
>
>
> The TaskAttemptID now includes the redundant copy of the JobTracker's start time as milliseconds.
We should instead change the JobID to have the longer unique string.

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