public class ChainMapper extends java.lang.Object implements Mapper
[MAP+ / REDUCE MAP*]
. And
immediate benefit of this pattern is a dramatic reduction in disk IO.
IMPORTANT: There is no need to specify the output key/value classes for the
ChainMapper, this is done by the addMapper for the last mapper in the chain.
ChainMapper usage pattern:
... conf.setJobName("chain"); conf.setInputFormat(TextInputFormat.class); conf.setOutputFormat(TextOutputFormat.class); JobConf mapAConf = new JobConf(false); ... ChainMapper.addMapper(conf, AMap.class, LongWritable.class, Text.class, Text.class, Text.class, true, mapAConf); JobConf mapBConf = new JobConf(false); ... ChainMapper.addMapper(conf, BMap.class, Text.class, Text.class, LongWritable.class, Text.class, false, mapBConf); JobConf reduceConf = new JobConf(false); ... ChainReducer.setReducer(conf, XReduce.class, LongWritable.class, Text.class, Text.class, Text.class, true, reduceConf); ChainReducer.addMapper(conf, CMap.class, Text.class, Text.class, LongWritable.class, Text.class, false, null); ChainReducer.addMapper(conf, DMap.class, LongWritable.class, Text.class, LongWritable.class, LongWritable.class, true, null); FileInputFormat.setInputPaths(conf, inDir); FileOutputFormat.setOutputPath(conf, outDir); ... JobClient jc = new JobClient(conf); RunningJob job = jc.submitJob(conf); ...
Constructor and Description |
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ChainMapper()
Constructor.
|
Modifier and Type | Method and Description |
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static <K1,V1,K2,V2> |
addMapper(JobConf job,
java.lang.Class<? extends Mapper<K1,V1,K2,V2>> klass,
java.lang.Class<? extends K1> inputKeyClass,
java.lang.Class<? extends V1> inputValueClass,
java.lang.Class<? extends K2> outputKeyClass,
java.lang.Class<? extends V2> outputValueClass,
boolean byValue,
JobConf mapperConf)
Adds a Mapper class to the chain job's JobConf.
|
void |
close()
Closes the ChainMapper and all the Mappers in the chain.
|
void |
configure(JobConf job)
Configures the ChainMapper and all the Mappers in the chain.
|
void |
map(java.lang.Object key,
java.lang.Object value,
OutputCollector output,
Reporter reporter)
Chains the
map(...) methods of the Mappers in the chain. |
public static <K1,V1,K2,V2> void addMapper(JobConf job, java.lang.Class<? extends Mapper<K1,V1,K2,V2>> klass, java.lang.Class<? extends K1> inputKeyClass, java.lang.Class<? extends V1> inputValueClass, java.lang.Class<? extends K2> outputKeyClass, java.lang.Class<? extends V2> outputValueClass, boolean byValue, JobConf mapperConf)
mapperConf
, have precedence over the job's JobConf. This
precedence is in effect when the task is running.
IMPORTANT: There is no need to specify the output key/value classes for the
ChainMapper, this is done by the addMapper for the last mapper in the chain
job
- job's JobConf to add the Mapper class.klass
- the Mapper class to add.inputKeyClass
- mapper input key class.inputValueClass
- mapper input value class.outputKeyClass
- mapper output key class.outputValueClass
- mapper output value class.byValue
- indicates if key/values should be passed by value
to the next Mapper in the chain, if any.mapperConf
- a JobConf with the configuration for the Mapper
class. It is recommended to use a JobConf without default values using the
JobConf(boolean loadDefaults)
constructor with FALSE.public void configure(JobConf job)
super.configure(...)
should be
invoked at the beginning of the overwriter method.configure
in interface JobConfigurable
job
- the configurationpublic void map(java.lang.Object key, java.lang.Object value, OutputCollector output, Reporter reporter) throws java.io.IOException
map(...)
methods of the Mappers in the chain.public void close() throws java.io.IOException
super.close()
should be
invoked at the end of the overwriter method.close
in interface java.io.Closeable
close
in interface java.lang.AutoCloseable
java.io.IOException
Copyright © 2009 The Apache Software Foundation