The reducer also serves as combiner whose output would be sent to reducer.
org.apache.hadoop.mapreduce.Reducer<Text, Text,
ImmutableBytesWritable, org.apache.hadoop.io.Writable>.Context context)
So the type parameters above should facilitate this.
Take a look at the PutCombiner from HBase source code:
public class PutCombiner<K> extends Reducer<K, Put, K, Put> {
Cheers
On Thu, Sep 5, 2013 at 9:46 AM, Shahab Yunus <[email protected]> wrote:
> Ted,
>
> Might be a something very basic that I am missing but why should OP's
> reducer's key be of type ImmutableBytesWritable if he is emitting Text in
> the mapper? Thanks.
>
> protected void map(
>
> ImmutableBytesWritable key,
>
> Result value,
>
> org.apache.hadoop.mapreduce.Mapper<ImmutableBytesWritable,
> Result, Text, Text>.Context context)
>
> throws IOException, InterruptedException {
>
> context.write(this.sentenseOriginal, this.sentenseParsed);
> //sentenseOriginal
> is Text
>
>
> Regards,
> Shahab
>
>
> On Thu, Sep 5, 2013 at 10:34 AM, Ted Yu <[email protected]> wrote:
>
> > public class SentimentCalculationHBaseReducer extends
> >
> > TableReducer<Text, Text, ImmutableBytesWritable> {
> >
> > The first type parameter for reducer should be ImmutableBytesWritable
> >
> > Cheers
> >
> >
> > On Wed, Sep 4, 2013 at 11:16 PM, Omkar Joshi <
> [email protected]
> > >wrote:
> >
> > > I'm trying to execute a MR code over stand-alone HBase(0.94.11). I had
> > > read the HBase api and modified my MR code to read data and getting
> > > exceptions in the Reduce phase.
> > >
> > > The exception I get is :
> > >
> > > 13/09/05 16:16:17 INFO mapred.JobClient: map 0% reduce 0%
> > >
> > > 13/09/05 16:23:31 INFO mapred.JobClient: Task Id :
> > > attempt_201309051437_0005_m_000000_0, Status : FAILED
> > >
> > > java.io.IOException: wrong key class: class
> > > org.apache.hadoop.hbase.io.ImmutableBytesWritable is not class
> > > org.apache.hadoop.io.Text
> > >
> > > at org.apache.hadoop.mapred.IFile$Writer.append(IFile.java:164)
> > >
> > > at
> > >
> >
> org.apache.hadoop.mapred.Task$CombineOutputCollector.collect(Task.java:1168)
> > >
> > > at
> > >
> >
> org.apache.hadoop.mapred.Task$NewCombinerRunner$OutputConverter.write(Task.java:1492)
> > >
> > > at
> > >
> >
> org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)
> > >
> > > at
> > >
> >
> com.hbase.mapreduce.SentimentCalculationHBaseReducer.reduce(SentimentCalculationHBaseReducer.java:199)
> > >
> > > at
> > >
> >
> com.hbase.mapreduce.SentimentCalculationHBaseReducer.reduce(SentimentCalculationHBaseReducer.java:1)
> > >
> > > at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:176)
> > >
> > > at
> > > org.apache.hadoop.mapred.Task$NewCombinerRunner.combine(Task.java:1513)
> > >
> > > at
> > >
> >
> org.apache.hadoop.mapred.MapTask$MapOutputBuffer.sortAndSpill(MapTask.java:1436)
> > >
> > > at
> > >
> org.apache.hadoop.mapred.MapTask$MapOutputBuffer.flush(MapTask.java:1298)
> > >
> > > at
> > >
> >
> org.apache.hadoop.mapred.MapTask$NewOutputCollector.close(MapTask.java:699)
> > >
> > > at
> > org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:766)
> > >
> > > at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
> > >
> > > at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
> > >
> > > at java.security.AccessController.doPrivileged(Native Method)
> > >
> > > at javax.security.auth.Subject.doAs(Subject.java:415)
> > >
> > > at
> > >
> >
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
> > >
> > > at org.apache.hadoop.mapred.Child.main(Child.java:249)
> > >
> > >
> > >
> > > Providing the partial(excluding the business logic) codes
> > >
> > >
> > > Mapper:
> > >
> > >
> > > public class SentimentCalculationHBaseMapper extends TableMapper<Text,
> > > Text> {
> > >
> > >
> > >
> > > private Text sentenseOriginal = new Text();
> > >
> > > private Text sentenseParsed = new Text();
> > >
> > >
> > >
> > > @Override
> > >
> > > protected void map(
> > >
> > > ImmutableBytesWritable key,
> > >
> > > Result value,
> > >
> > > org.apache.hadoop.mapreduce.Mapper<ImmutableBytesWritable,
> > > Result, Text, Text>.Context context)
> > >
> > > throws IOException, InterruptedException {
> > >
> > > context.write(this.sentenseOriginal, this.sentenseParsed);
> > >
> > > }
> > >
> > > }
> > >
> > > Reducer :
> > >
> > >
> > > public class SentimentCalculationHBaseReducer extends
> > >
> > > TableReducer<Text, Text, ImmutableBytesWritable> {
> > >
> > >
> > >
> > > @Override
> > >
> > > protected void reduce(
> > >
> > > Text key,
> > >
> > > java.lang.Iterable<Text> values,
> > >
> > > org.apache.hadoop.mapreduce.Reducer<Text, Text,
> > > ImmutableBytesWritable, org.apache.hadoop.io.Writable>.Context context)
> > >
> > > throws IOException, InterruptedException {
> > >
> > >
> > >
> > > Double mdblSentimentOverall = 0.0;
> > >
> > >
> > >
> > >
> > >
> > > String d3 = key + "@12321@" + s11.replaceFirst(":::", "")
> > >
> > > + "@12321@" + mstpositiveWords + "@12321@"
> > >
> > > + mstnegativeWords + "@12321@" + mstneutralWords;
> > >
> > >
> > >
> > > System.out.println("d3 : " + d3 + " , mdblSentimentOverall
> :
> > "
> > >
> > > + mdblSentimentOverall);
> > >
> > >
> > >
> > > Put put = new Put(d3.getBytes());
> > >
> > >
> > >
> > > put.add(Bytes.toBytes("word_attributes"),
> > >
> > > Bytes.toBytes("mdblSentimentOverall"),
> > >
> > > Bytes.toBytes(mdblSentimentOverall));
> > >
> > >
> > >
> > > System.out.println("Context is " + context);
> > >
> > >
> > >
> > > context.write(new ImmutableBytesWritable(d3.getBytes()),
> > put);
> > >
> > > }
> > >
> > > }
> > >
> > > SentimentCalculatorHBase - the Tool/main class :
> > > package com.hbase.mapreduce;
> > >
> > > import java.util.Calendar;
> > >
> > > import org.apache.hadoop.conf.Configuration;
> > > import org.apache.hadoop.conf.Configured;
> > > import org.apache.hadoop.hbase.client.Put;
> > > import org.apache.hadoop.hbase.client.Scan;
> > > import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
> > > import org.apache.hadoop.hbase.mapreduce.TableInputFormat;
> > > import org.apache.hadoop.hbase.mapreduce.TableMapReduceUtil;
> > > import org.apache.hadoop.hbase.mapreduce.TableOutputFormat;
> > > import org.apache.hadoop.io.Text;
> > > import org.apache.hadoop.mapreduce.Job;
> > > import org.apache.hadoop.util.Tool;
> > > import org.apache.hadoop.util.ToolRunner;
> > >
> > > public class SentimentCalculatorHBase extends Configured implements
> Tool
> > {
> > >
> > > /**
> > > * @param args
> > > * @throws Exception
> > > */
> > > public static void main(String[] args) throws Exception {
> > > // TODO Auto-generated method stub
> > > SentimentCalculatorHBase sentimentCalculatorHBase = new
> > > SentimentCalculatorHBase();
> > > ToolRunner.run(sentimentCalculatorHBase, args);
> > > }
> > >
> > > @Override
> > > public int run(String[] arg0) throws Exception {
> > > // TODO Auto-generated method stub
> > >
> > >
> > > System.out
> > > .println("***********************Configuration
> > > started***********************");
> > > Configuration configuration = getConf();
> > > System.out.println("Conf: " + configuration);
> > >
> > >
> > > Job sentiCalcJob = new Job(configuration, "HBase
> > > SentimentCalculation");
> > >
> > > sentiCalcJob.setJarByClass(SentimentCalculatorHBase.class);
> > >
> > sentiCalcJob.setMapperClass(SentimentCalculationHBaseMapper.class);
> > >
> > > sentiCalcJob.setCombinerClass(SentimentCalculationHBaseReducer.class);
> > >
> > > sentiCalcJob.setReducerClass(SentimentCalculationHBaseReducer.class);
> > >
> > >
> > > sentiCalcJob.setInputFormatClass(TableInputFormat.class);
> > > sentiCalcJob.setOutputFormatClass(TableOutputFormat.class);
> > >
> > > /* Start : Added out of exasperation! */
> > > sentiCalcJob.setOutputKeyClass(ImmutableBytesWritable.class);
> > > sentiCalcJob.setOutputValueClass(Put.class);
> > > /* End : Added out of exasperation! */
> > >
> > > Scan twitterdataUserScan = new Scan();
> > > twitterdataUserScan.setCaching(500);
> > >
> > > twitterdataUserScan.addColumn("word_attributes".getBytes(),
> > > "TwitterText".getBytes());
> > >
> > > TableMapReduceUtil.initTableMapperJob("twitterdata_user",
> > > twitterdataUserScan,
> > SentimentCalculationHBaseMapper.class,
> > > Text.class, Text.class, sentiCalcJob);
> > >
> > > TableMapReduceUtil.initTableReducerJob("sentiment_output",
> > > SentimentCalculationHBaseReducer.class, sentiCalcJob);
> > >
> > > Calendar beforeJob = Calendar.getInstance();
> > > System.out.println("Job Time started---------------- "
> > > + beforeJob.getTime());
> > > boolean check = sentiCalcJob.waitForCompletion(true);
> > > if (check == true) {
> > > System.out
> > > .println("*******************Job completed-
> > > SentimentCalculation********************");
> > > }
> > > Calendar afterJob = Calendar.getInstance();
> > > System.out
> > > .println("Job Time ended
> > > SentimentCalculation---------------- "
> > > + afterJob.getTime());
> > > return 0;
> > > }
> > > }
> > >
> > >
> > >
> > > Regards,
> > > Omkar Joshi
> > >
> > > ________________________________
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