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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