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The JobTracker should keep a track (with feedback from Reducers) of how many times a fetch for a particular map output failed. If this exceeds a certain threshold, then that map should be declared as lost, and should be reexecuted elsewhere. Based on the number of such complaints from Reducers, the JobTracker can blacklist the TaskTracker. This will make the framework reliable - it will take care of (faulty) TaskTrackers that sometimes always fail to serve up map outputs (for which exceptions are not properly raised/handled, for e.g., if the exception/problem happens in the Jetty server).
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Improvement
Closed
Major
JobTracker should collect statistics of failed map output fetches, and take decisions to reexecute map tasks and/or restart the (possibly faulty) Jetty server on the TaskTracker
