org.apache.hadoop.mapreduce

Interface ReduceContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

Type Parameters:

KEYIN - the class of the input keys

VALUEIN - the class of the input values

KEYOUT - the class of the output keys

VALUEOUT - the class of the output values

All Superinterfaces:

JobContext, org.apache.hadoop.util.Progressable, TaskAttemptContext, TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

All Known Implementing Classes:

ReduceContextImpl, Reducer.Context, WrappedReducer.Context

public interface ReduceContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>
extends TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

The context passed to the Reducer.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	ReduceContext.ValueIterator<VALUEIN> Iterator to iterate over values for a given group of records.

Field Summary

Fields inherited from interface org.apache.hadoop.mapreduce.JobContext

CACHE_ARCHIVES_VISIBILITIES, CACHE_FILE_VISIBILITIES, COMBINE_CLASS_ATTR, INPUT_FORMAT_CLASS_ATTR, JAR_UNPACK_PATTERN, JOB_ACL_MODIFY_JOB, JOB_ACL_VIEW_JOB, JOB_CANCEL_DELEGATION_TOKEN, JOB_NAMENODES, MAP_CLASS_ATTR, MAP_MEMORY_PHYSICAL_MB, MAP_OUTPUT_COLLECTOR_CLASS_ATTR, MAPREDUCE_TASK_CLASSPATH_PRECEDENCE, OUTPUT_FORMAT_CLASS_ATTR, PARTITIONER_CLASS_ATTR, REDUCE_CLASS_ATTR, REDUCE_MEMORY_PHYSICAL_MB, SHUFFLE_CONSUMER_PLUGIN_ATTR, USER_LOG_RETAIN_HOURS

Method Summary

Methods

Modifier and Type	Method and Description
java.lang.Iterable<VALUEIN>	getValues() Iterate through the values for the current key, reusing the same value object, which is stored in the context.
boolean	nextKey() Start processing next unique key.

Methods inherited from interface org.apache.hadoop.mapreduce.TaskInputOutputContext

getCurrentKey, getCurrentValue, getOutputCommitter, nextKeyValue, write

Methods inherited from interface org.apache.hadoop.mapreduce.TaskAttemptContext

getCounter, getCounter, getStatus, getTaskAttemptID, setStatus

Methods inherited from interface org.apache.hadoop.mapreduce.JobContext

getArchiveClassPaths, getArchiveTimestamps, getCacheArchives, getCacheFiles, getCombinerClass, getCombinerKeyGroupingComparator, getConfiguration, getCredentials, getFileClassPaths, getFileTimestamps, getGroupingComparator, getInputFormatClass, getJar, getJobID, getJobName, getJobSetupCleanupNeeded, getLocalCacheArchives, getLocalCacheFiles, getMapOutputKeyClass, getMapOutputValueClass, getMapperClass, getMaxMapAttempts, getMaxReduceAttempts, getNumReduceTasks, getOutputFormatClass, getOutputKeyClass, getOutputValueClass, getPartitionerClass, getProfileEnabled, getProfileParams, getReducerClass, getSortComparator, getSymlink, getUser, getWorkingDirectory, userClassesTakesPrecedence

Methods inherited from interface org.apache.hadoop.util.Progressable

progress

Method Detail

nextKey

boolean nextKey()
                throws java.io.IOException,
                       java.lang.InterruptedException

Start processing next unique key.

Throws:

java.io.IOException

java.lang.InterruptedException

getValues

java.lang.Iterable<VALUEIN> getValues()
                                      throws java.io.IOException,
                                             java.lang.InterruptedException

Iterate through the values for the current key, reusing the same value object, which is stored in the context.

Returns:

the series of values associated with the current key. All of the objects returned directly and indirectly from this method are reused.

Throws:

java.io.IOException

java.lang.InterruptedException