ExecDriver is the central class in co-ordinating execution of any map-reduce task.
ExecMapper is the generic Map class for Hive.
ExecReducer is the generic Reducer class for Hive.
HashTableLoader for MR loads the hashtable for MapJoins from local disk (hashtables are distributed by using the DistributedCache.
JobDebugger takes a RunningJob that has failed and grabs the top 4 failing tasks and outputs this information to the Hive CLI.
MapredLocalTask represents any local work (i.e.: client side work) that hive needs to execute.
Extension of ExecDriver: - can optionally spawn a map-reduce task from a separate jvm - will make last minute adjustments to map-reduce job parameters, viz: * estimating number of reducers * estimating whether job should run locally
Intelligence to make clients wait if the cluster is in a bad state.
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