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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1876) Persisting completed jobs status
Date Tue, 11 Sep 2007 06:46:32 GMT
Persisting completed jobs status
--------------------------------

                 Key: HADOOP-1876
                 URL: https://issues.apache.org/jira/browse/HADOOP-1876
             Project: Hadoop
          Issue Type: Improvement
          Components: mapred
         Environment: all
            Reporter: Alejandro Abdelnur
            Priority: Minor


Currently the JobTracker keeps information about completed jobs in memory. 

This information is  flushed from the cache when it has outlived (#RETIRE_JOB_INTERVAL) or
because the limit of completed jobs in memory has been reach (#MAX_COMPLETE_USER_JOBS_IN_MEMORY).


Also, if the JobTracker is restarted (due to being recycled or due to a crash) information
about completed jobs is lost.

If any of the above scenarios happens before the job information is queried by a hadoop client
(normally the job submitter or a monitoring component) there is no way to obtain such information.

A way to avoid this is the JobTracker to persist in DFS the completed jobs information upon
job completion. This would be done at the time the job is moved to the completed jobs queue.
Then when querying the JobTracker for information about a completed job, if it is not found
in the memory queue, a lookup  in DFS would be done to retrieve the completed job information.


A directory in DFS (under mapred/system) would be used to persist completed job information,
for each completed job there would be a directory with the job ID, within that directory all
the information about the job: status, jobprofile, counters and completion events.

A configuration property will indicate for how log persisted job information should be kept
in DFS. After such period it will be cleaned up automatically.

This improvement would not introduce API changes.


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