Affects Version/s: None
Fix Version/s: 0.16.0
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.