org.apache.hadoop.mapred.lib.aggregate

クラス ValueAggregatorReducer<K1 extends WritableComparable,V1 extends Writable>

java.lang.Object

org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase<K1,V1>

org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorReducer<K1,V1>

すべての実装されたインタフェース:

Closeable, AutoCloseable, JobConfigurable, Mapper<K1,V1,Text,Text>, Reducer<Text,Text,Text,Text>

@InterfaceAudience.Public
 @InterfaceStability.Stable
public class ValueAggregatorReducer<K1 extends WritableComparable,V1 extends Writable>
extends ValueAggregatorJobBase<K1,V1>

This class implements the generic reducer of Aggregate.

フィールドのサマリー

クラスから継承されたフィールド org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase

aggregatorDescriptorList

コンストラクタのサマリー

コンストラクタ

コンストラクタと説明
ValueAggregatorReducer()

メソッドのサマリー

修飾子とタイプ	メソッドと説明
void	map(K1 arg0, V1 arg1, OutputCollector<Text,Text> arg2, Reporter arg3) Do nothing.
void	reduce(Text key, Iterator<Text> values, OutputCollector<Text,Text> output, Reporter reporter) Reduces values for a given key.

クラスから継承されたメソッド org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase

close, configure, logSpec

クラスから継承されたメソッド java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

コンストラクタの詳細

ValueAggregatorReducer

public ValueAggregatorReducer()

メソッドの詳細

reduce

public void reduce(Text key,
                   Iterator<Text> values,
                   OutputCollector<Text,Text> output,
                   Reporter reporter)
            throws IOException

インタフェースからコピーされた説明: Reducer

Reduces values for a given key.

The 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 a significant 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 mapreduce.task.timeout to a high-enough value (or even zero for no time-outs).

パラメータ:

key - the key is expected to be a Text object, whose prefix indicates the type of aggregation to aggregate the values. In effect, data driven computing is achieved. It is assumed that each aggregator's getReport method emits appropriate output for the aggregator. This may be further customiized.

values - the values to be aggregated

output - to collect keys and combined values.

reporter - facility to report progress.

例外:

IOException

map

public void map(K1 arg0,
                V1 arg1,
                OutputCollector<Text,Text> arg2,
                Reporter arg3)
         throws IOException

Do nothing. Should not be called

パラメータ:

arg0 - the input key.

arg1 - the input value.

arg2 - collects mapped keys and values.

arg3 - facility to report progress.

例外:

IOException