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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1018) Single lost heartbeat leads to a "Lost task tracker"
Date Wed, 14 Feb 2007 02:05:06 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1018?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12472961
] 

Arun C Murthy commented on HADOOP-1018:
---------------------------------------

JobTracker does exactly what your suggested: acknowledge the duplicate status-update without
processsing; it resends the 'prevHeartbeatRespone'  i.e. the lost heartbeat response to the
TT. Maybe the log message there is misleading?

> Single lost heartbeat leads to a "Lost task tracker"
> ----------------------------------------------------
>
>                 Key: HADOOP-1018
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1018
>             Project: Hadoop
>          Issue Type: Bug
>    Affects Versions: 0.10.0, 0.11.2, 0.12.0
>         Environment: Nutch trunk/ (Hadoop 0.10.0), Linux, JDK 1.5, a cluster of 9 machines.
>            Reporter: Andrzej Bialecki 
>
> Under heavy load, task tracker may lose the heartbeat response from the JobTracker. Task
tracker tries to resend the last heartbeat message, which job tracker treats as "duplicate"
response and ignores. Since task tracker tries to resend the same heartbeat message, with
the same id, over and over again, no "valid" messages reach the job tracker, so after a while
it considers the task tracker to be lost. Task tracker cannot recover from this state and
needs to be restarted.
> Looking at Hadoop trunk/ I believe this problem still may occur - in JobTracker.java.heartbeat():992
JobTracker should not ignore duplicate messages but acknowledge them without processing. This
would cause the task tracker to sync back it's last heartbeat id with the last hearbeat id
remembered in the job tracker.

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