| Package | Description | 
|---|---|
| org.apache.hadoop.io | Generic i/o code for use when reading and writing data to the network,
to databases, and to files. | 
| org.apache.hadoop.io.serializer | 
This package provides a mechanism for using different serialization frameworks
in Hadoop. | 
| org.apache.hadoop.mapred | |
| org.apache.hadoop.mapreduce | |
| org.apache.hadoop.mapreduce.lib.partition | |
| org.apache.hadoop.record | 
    (DEPRECATED) Hadoop record I/O contains classes and a record description language
    translator for simplifying serialization and deserialization of records in a
    language-neutral manner. | 
| Modifier and Type | Class and Description | 
|---|---|
| class  | WritableComparatorA Comparator for  WritableComparables. | 
| Modifier and Type | Class and Description | 
|---|---|
| class  | org.apache.hadoop.io.serializer.DeserializerComparator<T>
 A  RawComparatorthat uses aDeserializerto deserialize
 the objects to be compared so that the standardComparatorcan
 be used to compare them. | 
| class  | JavaSerializationComparator<T extends Serializable & Comparable<T>>
 A  RawComparatorthat uses aJavaSerializationDeserializerto deserialize objects that are then compared via
 theirComparableinterfaces. | 
| Modifier and Type | Method and Description | 
|---|---|
| RawComparator | JobConf. getCombinerKeyGroupingComparator()Get the user defined  WritableComparablecomparator for
 grouping keys of inputs to the combiner. | 
| RawComparator | JobConf. getOutputKeyComparator()Get the  RawComparatorcomparator used to compare keys. | 
| RawComparator | JobConf. getOutputValueGroupingComparator()Get the user defined  WritableComparablecomparator for 
 grouping keys of inputs to the reduce. | 
| Modifier and Type | Method and Description | 
|---|---|
| void | JobConf. setCombinerKeyGroupingComparator(Class<? extends RawComparator> theClass)Set the user defined  RawComparatorcomparator for
 grouping keys in the input to the combiner. | 
| void | JobConf. setOutputKeyComparatorClass(Class<? extends RawComparator> theClass)Set the  RawComparatorcomparator used to compare keys. | 
| void | JobConf. setOutputValueGroupingComparator(Class<? extends RawComparator> theClass)Set the user defined  RawComparatorcomparator for 
 grouping keys in the input to the reduce. | 
| Modifier and Type | Method and Description | 
|---|---|
| RawComparator<?> | JobContext. getCombinerKeyGroupingComparator()Get the user defined  RawComparatorcomparator for
 grouping keys of inputs to the combiner. | 
| RawComparator<?> | JobContext. getGroupingComparator()Get the user defined  RawComparatorcomparator for
 grouping keys of inputs to the reduce. | 
| RawComparator<?> | JobContext. getSortComparator()Get the  RawComparatorcomparator used to compare keys. | 
| Modifier and Type | Method and Description | 
|---|---|
| void | Job. setCombinerKeyGroupingComparatorClass(Class<? extends RawComparator> cls)Define the comparator that controls which keys are grouped together
 for a single call to combiner,
  Reducer.reduce(Object, Iterable,
 org.apache.hadoop.mapreduce.Reducer.Context) | 
| void | Job. setGroupingComparatorClass(Class<? extends RawComparator> cls)Define the comparator that controls which keys are grouped together
 for a single call to 
  Reducer.reduce(Object, Iterable, 
                       org.apache.hadoop.mapreduce.Reducer.Context) | 
| void | Job. setSortComparatorClass(Class<? extends RawComparator> cls)Define the comparator that controls how the keys are sorted before they
 are passed to the  Reducer. | 
| Modifier and Type | Class and Description | 
|---|---|
| class  | KeyFieldBasedComparator<K,V>This comparator implementation provides a subset of the features provided
 by the Unix/GNU Sort. | 
| Modifier and Type | Class and Description | 
|---|---|
| class  | RecordComparatorDeprecated. 
 Replaced by Avro. | 
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