首页 > 代码库 > MapReduce 编程 系列八 Reducer数目
MapReduce 编程 系列八 Reducer数目
本篇介绍如何控制reduce的数目。前面观察结果文件,都会发现一般是以part-r-00000 形式出现多个文件,其实这个reducer的数目有关系,reducer数目多,结果文件数目就多。
在初始化job的时候,是可以设置reducer的数目的。example4在example的基础上做了改动。修改了pom.xml,使得结束一个参数作为reducer的数目。修改了LogJob.java的代码,作为设置reducer数目。
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org.freebird</groupId> <artifactId>mr1_example4</artifactId> <packaging>jar</packaging> <version>1.0-SNAPSHOT</version> <name>mr1_example4</name> <url>http://maven.apache.org</url> <dependencies> <dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-core</artifactId> <version>1.2.1</version> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>exec-maven-plugin</artifactId> <version>1.3.2</version> <executions> <execution> <goals> <goal>exec</goal> </goals> </execution> </executions> <configuration> <executable>hadoop</executable> <arguments> <argument>jar</argument> <argument>target/mr1_example4-1.0-SNAPSHOT.jar</argument> <argument>org.freebird.LogJob</argument> <argument>/user/chenshu/share/logs</argument> <argument>1</argument> </arguments> </configuration> </plugin> </plugins> </build> </project>
import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.fs.Path; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.freebird.reducer.LogReducer; import org.freebird.mapper.LogMapper; import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat; import org.apache.hadoop.mapreduce.lib.output.MultipleOutputs; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.fs.FileSystem; import java.io.IOException; public class LogJob { public static void main(String[] args) throws Exception { String inputPath = args[0]; if (inputPath.endsWith("/")) { inputPath = inputPath.substring(0, inputPath.length() -1); } System.out.println("args[0] indicates input folder path, the last / will be removed if it exists:" + inputPath); String outputPath = inputPath + "/output"; System.out.println("output folder path is:" + outputPath); int numReducer = Integer.parseInt(args[1]); System.out.println("reducer number is: " + args[1]); Configuration conf = new Configuration(); Job job = new Job(conf, "sum_did_from_log_file"); job.setJarByClass(LogJob.class); job.setMapperClass(org.freebird.mapper.LogMapper.class); job.setReducerClass(org.freebird.reducer.LogReducer.class); job.setNumReduceTasks(numReducer); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); Path path1 = new Path(inputPath); Path path2 = new Path(outputPath); removeFolder(path2, conf); MultipleOutputs.addNamedOutput(job, "result", TextOutputFormat.class, Text.class, IntWritable.class); FileInputFormat.addInputPath(job, path1); FileOutputFormat.setOutputPath(job, path2); System.exit(job.waitForCompletion(true) ? 0 : 1); } private static void removeFolder(Path path, Configuration conf) throws IOException { FileSystem fs = path.getFileSystem(conf); if (fs.exists(path)) { fs.delete(path); } } }
运行结果,通过观察jobtracker,的确reducer数目为1了。并且结果文件也变成了只有一个:
[chenshu@hadoopMaster example4]$ hdfs dfs -ls /user/chenshu/share/logs/output/ 14/10/03 14:18:35 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable Found 4 items -rw-r--r-- 3 chenshu chenshu 0 2014-10-03 12:53 /user/chenshu/share/logs/output/_SUCCESS drwxr-xr-x - chenshu chenshu 0 2014-10-03 12:52 /user/chenshu/share/logs/output/_logs -rw-r--r-- 3 chenshu chenshu 0 2014-10-03 12:53 /user/chenshu/share/logs/output/part-r-00000 -rw-r--r-- 3 chenshu chenshu 4391668 2014-10-03 12:53 /user/chenshu/share/logs/output/result-r-00000
MapReduce 编程 系列八 Reducer数目
声明:以上内容来自用户投稿及互联网公开渠道收集整理发布,本网站不拥有所有权,未作人工编辑处理,也不承担相关法律责任,若内容有误或涉及侵权可进行投诉: 投诉/举报 工作人员会在5个工作日内联系你,一经查实,本站将立刻删除涉嫌侵权内容。