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Posted to mapreduce-issues@hadoop.apache.org by "Jason Lowe (JIRA)" <ji...@apache.org> on 2012/10/08 22:20:02 UTC
[jira] [Created] (MAPREDUCE-4714) Historyserver retrieves job from
jobID more often than necessary
Jason Lowe created MAPREDUCE-4714:
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Summary: Historyserver retrieves job from jobID more often than necessary
Key: MAPREDUCE-4714
URL: https://issues.apache.org/jira/browse/MAPREDUCE-4714
Project: Hadoop Map/Reduce
Issue Type: Bug
Components: jobhistoryserver, mrv2
Affects Versions: 2.0.0-alpha, 0.23.3
Reporter: Jason Lowe
Priority: Minor
When serving up a web page for job history, AppController.requireJob() is converting from a jobID to a job twice when it only needs to do it once. The resulting job is stored into the app object, which we could, in turn, use in historyserver web page render() methods to simply retrieve the job rather than performing yet another jobID->job lookup. That would cut the job lookups down from 3 to 1.
jobID->job lookups aren't necessarily cheap. If the job isn't in the historyserver joblist cache then the historyserver needs to scan directories looking for it, adding an unnecessary extra load onto the namenode.
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