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java.lang.Objectorg.apache.hadoop.streaming.PipeMapRed
org.apache.hadoop.streaming.PipeReducer
public class PipeReducer
A generic Reducer bridge. It delegates operations to an external program via stdin and stdout.
| Field Summary |
|---|
| Fields inherited from class org.apache.hadoop.streaming.PipeMapRed |
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LOG, outerrThreadsThrowable |
| Constructor Summary | |
|---|---|
PipeReducer()
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| Method Summary | |
|---|---|
void |
close()
|
void |
configure(JobConf job)
Initializes a new instance from a JobConf. |
byte[] |
getFieldSeparator()
Returns the field separator to be used. |
byte[] |
getInputSeparator()
Returns the input separator to be used. |
int |
getNumOfKeyFields()
Returns the number of key fields. |
void |
reduce(Object key,
Iterator values,
OutputCollector output,
Reporter reporter)
Reduces values for a given key. |
| Methods inherited from class org.apache.hadoop.streaming.PipeMapRed |
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getClientInput, getClientOutput, getConfiguration, getContext, mapRedFinished |
| Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Constructor Detail |
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public PipeReducer()
| Method Detail |
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public void configure(JobConf job)
JobConfigurableJobConf.
configure in interface JobConfigurableconfigure in class PipeMapRedjob - the configuration
public void reduce(Object key,
Iterator values,
OutputCollector output,
Reporter reporter)
throws IOException
ReducerThe framework calls this method for each
<key, (list of values)> pair in the grouped inputs.
Output values must be of the same type as input values. Input keys must
not be altered. The framework will reuse the key and value objects
that are passed into the reduce, therefore the application should clone
the objects they want to keep a copy of. In many cases, all values are
combined into zero or one value.
Output pairs are collected with calls to
OutputCollector.collect(Object,Object).
Applications can use the Reporter provided to report progress
or just indicate that they are alive. In scenarios where the application
takes an insignificant amount of time to process individual key/value
pairs, this is crucial since the framework might assume that the task has
timed-out and kill that task. The other way of avoiding this is to set
mapred.task.timeout to a high-enough value (or even zero for no
time-outs).
reduce in interface Reducerkey - the key.values - the list of values to reduce.output - to collect keys and combined values.reporter - facility to report progress.
IOExceptionpublic void close()
close in interface Closeablepublic byte[] getInputSeparator()
PipeMapRed
getInputSeparator in class PipeMapRedpublic byte[] getFieldSeparator()
PipeMapRed
getFieldSeparator in class PipeMapRedpublic int getNumOfKeyFields()
PipeMapRed
getNumOfKeyFields in class PipeMapRed
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