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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1876) Persisting completed jobs status
Date Wed, 09 Jan 2008 19:47:34 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1876?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12557397#action_12557397
] 

Arun C Murthy commented on HADOOP-1876:
---------------------------------------

bq. Can this patch make JobHistory log obsolete? Or at least is that intended? I hate to see
same information logged at different places in different forms using different code paths.

This patch doesn't do that, but definitely that is the direction I'd go too... +1.

Should we broaden the scope HADOOP-2178 to re-work JobHistory to use Writables rather than
the custom format? Or is that a new jira?

bq. Other than being in text format (which has its pros and cons), job history log is event
based [...]

Yes, moving to Writable wouldn't hurt the _job analysis_ part since, as you point out, it's
event-based - we just need to use Writable.readFields rather than the custom text-parsing...
anyone sees other issues?



> 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
>            Assignee: Alejandro Abdelnur
>            Priority: Critical
>             Fix For: 0.16.0
>
>         Attachments: patch1876.txt, patch1876.txt
>
>
> 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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