MapReduce作業：奇怪的輸出？

Question

我正在寫我的第一份MapReduce工作。 簡單的事情：只計算文件中的字母數字字符。 我已經完成了生成我的jar文件並運行它的工作，但是除了調試輸出之外，我找不到MR作業的輸出。 請你幫助我好嗎？

我的應用程序類：

import CharacterCountMapper;
import CharacterCountReducer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class CharacterCountDriver extends Configured implements Tool {

    @Override
    public int run(String[] args) throws Exception {

        // Create a JobConf using the processed configuration processed by ToolRunner
        Job job = Job.getInstance(getConf());

        // Process custom command-line options
        Path in = new Path("/tmp/filein");
        Path out = new Path("/tmp/fileout");

        // Specify various job-specific parameters     
        job.setJobName("Character-Count");

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        job.setMapperClass(CharacterCountMapper.class);
        job.setReducerClass(CharacterCountReducer.class);

        job.setInputFormatClass(TextInputFormat.class);
        job.setOutputFormatClass(TextOutputFormat.class);

        FileInputFormat.setInputPaths(job, in);
        FileOutputFormat.setOutputPath(job, out);

        job.setJarByClass(CharacterCountDriver.class);

        job.submit();
        return 0;
    }

    public static void main(String[] args) throws Exception {
        // Let ToolRunner handle generic command-line options 
        int res = ToolRunner.run(new Configuration(), new CharacterCountDriver(), args);

        System.exit(res);
      }
}

然后我的映射器類：

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class CharacterCountMapper extends
        Mapper<Object, Text, Text, IntWritable> {

    private final static IntWritable one = new IntWritable(1);

    @Override
    protected void map(Object key, Text value, Context context)
            throws IOException, InterruptedException {
        String strValue = value.toString();
        StringTokenizer chars = new StringTokenizer(strValue.replaceAll("[^a-zA-Z0-9]", ""));
        while (chars.hasMoreTokens()) {
            context.write(new Text(chars.nextToken()), one);
        }
    }
}

減速器：

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class CharacterCountReducer extends
        Reducer<Text, IntWritable, Text, IntWritable> {

    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context)
            throws IOException, InterruptedException {
        int charCount = 0;
        for (IntWritable val: values) {
            charCount += val.get();
        }
        context.write(key, new IntWritable(charCount));
    }
}

看起來不錯，我從IDE生成了可運行的jar文件，並按如下所示執行它：

$ ./hadoop jar ~/Desktop/example_MapReduce.jar no.hib.mod250.hadoop.CharacterCountDriver
14/11/27 19:36:42 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id
14/11/27 19:36:42 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
14/11/27 19:36:42 INFO input.FileInputFormat: Total input paths to process : 1
14/11/27 19:36:42 INFO mapreduce.JobSubmitter: number of splits:1
14/11/27 19:36:43 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_local316715466_0001
14/11/27 19:36:43 WARN conf.Configuration: file:/tmp/hadoop-roberto/mapred/staging/roberto316715466/.staging/job_local316715466_0001/job.xml:an attempt to override final parameter: mapreduce.job.end-notification.max.retry.interval;  Ignoring.
14/11/27 19:36:43 WARN conf.Configuration: file:/tmp/hadoop-roberto/mapred/staging/roberto316715466/.staging/job_local316715466_0001/job.xml:an attempt to override final parameter: mapreduce.job.end-notification.max.attempts;  Ignoring.
14/11/27 19:36:43 WARN conf.Configuration: file:/tmp/hadoop-roberto/mapred/local/localRunner/roberto/job_local316715466_0001/job_local316715466_0001.xml:an attempt to override final parameter: mapreduce.job.end-notification.max.retry.interval;  Ignoring.
14/11/27 19:36:43 WARN conf.Configuration: file:/tmp/hadoop-roberto/mapred/local/localRunner/roberto/job_local316715466_0001/job_local316715466_0001.xml:an attempt to override final parameter: mapreduce.job.end-notification.max.attempts;  Ignoring.
14/11/27 19:36:43 INFO mapreduce.Job: The url to track the job: http://localhost:8080/
14/11/27 19:36:43 INFO mapred.LocalJobRunner: OutputCommitter set in config null
14/11/27 19:36:43 INFO mapred.LocalJobRunner: OutputCommitter is org.apache.hadoop.mapreduce.lib.output.FileOutputCommitter
14/11/27 19:36:43 INFO mapred.LocalJobRunner: Waiting for map tasks
14/11/27 19:36:43 INFO mapred.LocalJobRunner: Starting task: attempt_local316715466_0001_m_000000_0
14/11/27 19:36:43 INFO mapred.Task:  Using ResourceCalculatorProcessTree : [ ]
14/11/27 19:36:43 INFO mapred.MapTask: Processing split: file:/tmp/filein:0+434
14/11/27 19:36:43 INFO mapred.MapTask: Map output collector class = org.apache.hadoop.mapred.MapTask$MapOutputBuffer

然后我猜我的輸出文件將在/ tmp / fileout中。 但是，它似乎是空的：

$ tree /tmp/fileout/
/tmp/fileout/
└── _temporary
    └── 0

2 directories, 0 files

有什么我想念的嗎？ 誰能幫我嗎？

問候 ：-）

編輯：

我幾乎在另一篇文章中找到了解決方案。

在CharacterCountDriver中，我用job.waitForCompletion（true）替換了job.submit（）。 我得到了更詳細的輸出：

/tmp/fileout/
├── part-r-00000
└── _SUCCESS

0 directories, 2 files

但是我仍然不知道該怎么讀，_SUCCESS是空的，part-r-0000不是我所期望的：

Absorbantandyellowandporousishe 1
AreyoureadykidsAyeAyeCaptain    1
ICanthearyouAYEAYECAPTAIN       1
Ifnauticalnonsensebesomethingyouwish    1
Ohh     1
READY   1
SPONGEBOBSQUAREPANTS    1
SpongebobSquarepants    3
Spongebobsquarepants    4
Thendroponthedeckandfloplikeafish       1
Wholivesinapineappleunderthesea 1

有什么建議嗎？ 我的代碼中可能有任何錯誤嗎？ 謝謝。

Answer 1

part-r-00000是減速器輸出文件的名稱。 如果您有更多的減速器，它們將被編號為r-00001，以此類推。

Answer 2

如果我理解正確，則您希望程序對輸入文件中的字母數字字符計數。 但是，這不是您的代碼在做什么。 您可以更改映射器以計算每行中的字母數字字符：

String strValue = value.toString();
strValue.replaceAll("[^a-zA-Z0-9]", "");
context.write(new Text("alphanumeric", strValue.length());

這應該可以修復您的程序。 基本上，您的映射器將每行中的字母數字字符作為鍵輸出。 減速器累積每個鍵的計數。 進行我的更改后，您只需使用一個鍵：“字母數字”。 密鑰可能是其他東西，並且仍然可以使用。