| Class and Description | 
|---|
| ClusterStatus Status information on the current state of the Map-Reduce cluster. | 
| Counters A set of named counters. | 
| Counters.Counter A counter record, comprising its name and value. | 
| Counters.Group Groupof counters, comprising of counters from a particular
  counterEnumclass. | 
| FileAlreadyExistsException Used when target file already exists for any operation and 
 is not configured to be overwritten. | 
| FileInputFormat A base class for file-based  InputFormat. | 
| FileOutputFormat A base class for  OutputFormat. | 
| FileSplit A section of an input file. | 
| InputFormat InputFormatdescribes the input-specification for a 
 Map-Reduce job. | 
| InputSplit InputSplitrepresents the data to be processed by an 
 individualMapper. | 
| InputSplitWithLocationInfo | 
| InvalidJobConfException This exception is thrown when jobconf misses some mendatory attributes
 or value of some attributes is invalid. | 
| JobConf A map/reduce job configuration. | 
| JobConfigurable That what may be configured. | 
| JobContext | 
| JobID JobID represents the immutable and unique identifier for 
 the job. | 
| JobPriority Used to describe the priority of the running job. | 
| JobQueueInfo Class that contains the information regarding the Job Queues which are 
 maintained by the Hadoop Map/Reduce framework. | 
| JobStatus Describes the current status of a job. | 
| Mapper Maps input key/value pairs to a set of intermediate key/value pairs. | 
| MapRunnable Expert: Generic interface for  Mappers. | 
| OutputCollector | 
| OutputCommitter OutputCommitterdescribes the commit of task output for a 
 Map-Reduce job. | 
| OutputFormat OutputFormatdescribes the output-specification for a 
 Map-Reduce job. | 
| Partitioner Partitions the key space. | 
| RecordReader RecordReaderreads <key, value> pairs from anInputSplit. | 
| RecordWriter RecordWriterwrites the output <key, value> pairs 
 to an output file. | 
| Reducer Reduces a set of intermediate values which share a key to a smaller set of
 values. | 
| Reporter A facility for Map-Reduce applications to report progress and update 
 counters, status information etc. | 
| RunningJob RunningJobis the user-interface to query for details on a 
 running Map-Reduce job. | 
| SequenceFileInputFormat An  InputFormatforSequenceFiles. | 
| SequenceFileOutputFormat An  OutputFormatthat writesSequenceFiles. | 
| SplitLocationInfo | 
| TaskAttemptContext | 
| TaskAttemptID TaskAttemptID represents the immutable and unique identifier for 
 a task attempt. | 
| TaskCompletionEvent This is used to track task completion events on 
 job tracker. | 
| TaskCompletionEvent.Status | 
| TaskID TaskID represents the immutable and unique identifier for 
 a Map or Reduce Task. | 
| TaskReport A report on the state of a task. | 
| Class and Description | 
|---|
| JobClient JobClientis the primary interface for the user-job to interact
 with the cluster. | 
| JobConf A map/reduce job configuration. | 
| JobID JobID represents the immutable and unique identifier for 
 the job. | 
| Class and Description | 
|---|
| InputFormat InputFormatdescribes the input-specification for a 
 Map-Reduce job. | 
| InputSplit InputSplitrepresents the data to be processed by an 
 individualMapper. | 
| JobConf A map/reduce job configuration. | 
| RecordReader RecordReaderreads <key, value> pairs from anInputSplit. | 
| Reporter A facility for Map-Reduce applications to report progress and update 
 counters, status information etc. | 
| Class and Description | 
|---|
| FileInputFormat A base class for file-based  InputFormat. | 
| FileOutputFormat A base class for  OutputFormat. | 
| FileSplit A section of an input file. | 
| InputFormat InputFormatdescribes the input-specification for a 
 Map-Reduce job. | 
| InputSplit InputSplitrepresents the data to be processed by an 
 individualMapper. | 
| JobConf A map/reduce job configuration. | 
| JobConfigurable That what may be configured. | 
| Mapper Maps input key/value pairs to a set of intermediate key/value pairs. | 
| MapReduceBase | 
| MapRunnable Expert: Generic interface for  Mappers. | 
| OutputCollector | 
| OutputFormat OutputFormatdescribes the output-specification for a 
 Map-Reduce job. | 
| Partitioner Partitions the key space. | 
| RecordReader RecordReaderreads <key, value> pairs from anInputSplit. | 
| RecordWriter RecordWriterwrites the output <key, value> pairs 
 to an output file. | 
| Reducer Reduces a set of intermediate values which share a key to a smaller set of
 values. | 
| Reporter A facility for Map-Reduce applications to report progress and update 
 counters, status information etc. | 
| Class and Description | 
|---|
| JobConf A map/reduce job configuration. | 
| JobConfigurable That what may be configured. | 
| Mapper Maps input key/value pairs to a set of intermediate key/value pairs. | 
| OutputCollector | 
| Reducer Reduces a set of intermediate values which share a key to a smaller set of
 values. | 
| Reporter A facility for Map-Reduce applications to report progress and update 
 counters, status information etc. | 
| Class and Description | 
|---|
| InputFormat InputFormatdescribes the input-specification for a 
 Map-Reduce job. | 
| InputSplit InputSplitrepresents the data to be processed by an 
 individualMapper. | 
| JobConf A map/reduce job configuration. | 
| JobConfigurable That what may be configured. | 
| OutputFormat OutputFormatdescribes the output-specification for a 
 Map-Reduce job. | 
| RecordReader RecordReaderreads <key, value> pairs from anInputSplit. | 
| RecordWriter RecordWriterwrites the output <key, value> pairs 
 to an output file. | 
| Reporter A facility for Map-Reduce applications to report progress and update 
 counters, status information etc. | 
| Class and Description | 
|---|
| JobConf A map/reduce job configuration. | 
| RunningJob RunningJobis the user-interface to query for details on a 
 running Map-Reduce job. | 
| Class and Description | 
|---|
| ID A general identifier, which internally stores the id
 as an integer. | 
| SplitLocationInfo | 
| TaskCompletionEvent This is used to track task completion events on 
 job tracker. | 
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