MapReduce(四) 典型编程场景（二）
一、MapJoin-DistributedCache 应用
1、mapreduce join 介绍
在各种实际业务场景中，按照某个关键字对两份数据进行连接是非常常见的。如果两份数据 都比较小，那么可以直接在内存中完成连接。如果是大数据量的呢？ 显然，在内存中进行连 接会发生 OOM。 MapReduce 可以用来解决大数据量的链接
MapReduce 的 Join 操作主要分两类： MapJoin 和 ReduceJoin
先看 ReduceJoin:
（1）map 阶段，两份数据 data1 和 data2 会被 map 分别读入，解析成以链接字段为 key 以查 询字段为 value 的 key-value 对，并标明数据来源是 data1 还是 data2。
（2）reduce 阶段， reducetask 会接收来自 data1 和 data2 的相同 key 的数据，在 reduce 端进 行乘积链接， 最直接的影响是很消耗内存，导致 OOM
再看 MapJoin:
MapJoin 适用于有一份数据较小的连接情况。做法是直接把该小份数据直接全部加载到内存 当中，按链接关键字建立索引。 然后大份数据就作为 MapTask 的输入，对 map()方法的每次 输入都去内存当中直接去匹配连接。 然后把连接结果按 key 输出，这种方法要使用 hadoop
中的 DistributedCache 把小份数据分布到各个计算节点，每个 maptask 执行任务的节点都需 要加载该数据到内存，并且按连接关键字建立索引
（map读的是大表数据，在读大表之前，把小表数据放到内存当中，用setup方法）
2、需求
现有两份数据 movies.dat 和 ratings.dat 数据样式分别为：
Movies.dat：
1::Toy Story (1995)::Animation|Children's|Comedy
2::Jumanji (1995)::Adventure|Children's|Fantasy
3::Grumpier Old Men (1995)::Comedy|Romance
字段含义： movieid, moviename, movietype
Ratings.dat
1::1193::5::978300760
1::661::3::978302109
1::914::3::978301968
字段含义： userid, movieid, rate, timestamp
现要求对两表进行连接，要求输出最终的结果有以上六个字段：
movieid, userid, rate, moviename, movietype, timestamp
3、实现
第一步：封装 MovieRate,方便数据的排序和序列化
package com.ghgj.mr.mymapjoin;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.WritableComparable;
public class MovieRate implements WritableComparable<MovieRate>{
private String movieid;
private String userid;
private int rate;
private String movieName;
private String movieType;
private long ts;
public String getMovieid() {
return movieid;
}
public void setMovieid(String movieid) {
this.movieid = movieid;
}
public String getUserid() {
return userid;
}
public void setUserid(String userid) {
this.userid = userid;
}
public int getRate() {
return rate;
}
public void setRate(int rate) {
this.rate = rate;
}
public String getMovieName() {
return movieName;
}
public void setMovieName(String movieName) {
this.movieName = movieName;
}
public String getMovieType() {
return movieType;
}
public void setMovieType(String movieType) {
this.movieType = movieType;
}
public long getTs() {
return ts;
}
public void setTs(long ts) {
this.ts = ts;
}
public MovieRate() {
}
public MovieRate(String movieid, String userid, int rate, String movieName,
String movieType, long ts) {
this.movieid = movieid;
this.userid = userid;
this.rate = rate;
this.movieName = movieName;
this.movieType = movieType;
this.ts = ts;
}
@Override
public String toString() {
return movieid + "\t" + userid + "\t" + rate + "\t" + movieName
+ "\t" + movieType + "\t" + ts;
}
@Override
public void write(DataOutput out) throws IOException {
out.writeUTF(movieid);
out.writeUTF(userid);
out.writeInt(rate);
out.writeUTF(movieName);
out.writeUTF(movieType);
out.writeLong(ts);
}
@Override
public void readFields(DataInput in) throws IOException {
this.movieid = in.readUTF();
this.userid = in.readUTF();
this.rate = in.readInt();
this.movieName = in.readUTF();
this.movieType = in.readUTF();
this.ts = in.readLong();
}
@Override
public int compareTo(MovieRate mr) {
int it = mr.getMovieid().compareTo(this.movieid);
if(it == 0){
return mr.getUserid().compareTo(this.userid);
}else{
return it;
}
}
}
第二步：编写mapreduce程序
package com.ghgj.mr.mymapjoin;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.net.URI;
import java.util.HashMap;
import java.util.Map;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.filecache.DistributedCache;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class MovieRatingMapJoinMR {
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
conf.set("fs.defaultFS", "hdfs://hadoop02:9000");
System.setProperty("HADOOP_USER_NAME","hadoop");
Job job = Job.getInstance(conf);
// job.setJarByClass(MovieRatingMapJoinMR.class);
job.setJar("/home/hadoop/mrmr.jar");
job.setMapperClass(MovieRatingMapJoinMRMapper.class);
job.setMapOutputKeyClass(MovieRate.class);
job.setMapOutputValueClass(NullWritable.class);
// job.setReducerClass(MovieRatingMapJoinMReducer.class);
// job.setOutputKeyClass(MovieRate.class);
// job.setOutputValueClass(NullWritable.class);
job.setNumReduceTasks(0);
String minInput = args[0];
String maxInput = args[1];
String output = args[2];
FileInputFormat.setInputPaths(job, new Path(maxInput));
Path outputPath = new Path(output);
FileSystem fs = FileSystem.get(conf);
if(fs.exists(outputPath)){
fs.delete(outputPath, true);
}
FileOutputFormat.setOutputPath(job, outputPath);
URI uri = new Path(minInput).toUri();
job.addCacheFile(uri);
boolean status = job.waitForCompletion(true);
System.exit(status?0:1);
}
二、自定义 OutputFormat—数据分类输出
实现：自定义 OutputFormat，改写其中的 RecordWriter，改写具体输出数据的方法 write()
package com.ghgj.mr.score_outputformat;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
public class MyScoreOutputFormat extends TextOutputFormat<Text, NullWritable>{
@Override
public RecordWriter<Text, NullWritable> getRecordWriter(
TaskAttemptContext job) throws IOException, InterruptedException {
Configuration configuration = job.getConfiguration();
FileSystem fs = FileSystem.get(configuration);
Path p1 = new Path("/score1/outpu1");
Path p2 = new Path("/score2/outpu2");
if(fs.exists(p1)){
fs.delete(p1, true);
}
if(fs.exists(p2)){
fs.delete(p2, true);
}
FSDataOutputStream fsdout1 = fs.create(p1);
FSDataOutputStream fsdout2 = fs.create(p2);
return new MyRecordWriter(fsdout1, fsdout2);
}
static class MyRecordWriter extends RecordWriter<Text, NullWritable>{
FSDataOutputStream dout1 = null;
FSDataOutputStream dout2 = null;
public MyRecordWriter(FSDataOutputStream dout1, FSDataOutputStream dout2) {
super();
this.dout1 = dout1;
this.dout2 = dout2;
}
@Override
public void write(Text key, NullWritable value) throws IOException,
InterruptedException {
// TODO Auto-generated method stub
String[] strs = key.toString().split("::");
if(strs[0].equals("1")){
dout1.writeBytes(strs[1]+"\n");
}else{
dout2.writeBytes(strs[1]+"\n");
}
}
@Override
public void close(TaskAttemptContext context) throws IOException,
InterruptedException {
IOUtils.closeStream(dout2);
IOUtils.closeStream(dout1);
}
}
}
package com.ghgj.mr.score_outputformat;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
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.util.Tool;
import org.apache.hadoop.util.ToolRunner;
public class ScoreOutputFormatMR extends Configured implements Tool{
// 这个run方法就相当于Driver
@Override
public int run(String[] args) throws Exception {
Configuration conf = new Configuration();
conf.set("fs.defaultFS", "hdfs://hadoop02:9000");
System.setProperty("HADOOP_USER_NAME", "hadoop");
Job job = Job.getInstance(conf);
job.setMapperClass(ScoreOutputFormatMRMapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(NullWritable.class);
job.setNumReduceTasks(0);
// 这就是默认的输入输出组件
job.setInputFormatClass(TextInputFormat.class);
// 这是默认往外输出数据的组件
// job.setOutputFormatClass(TextOutputFormat.class);
job.setOutputFormatClass(MyScoreOutputFormat.class);
FileInputFormat.setInputPaths(job, new Path("/scorefmt"));
Path output = new Path("/scorefmt/output");
FileSystem fs = FileSystem.get(conf);
if(fs.exists(output)){
fs.delete(output, true);
}
FileOutputFormat.setOutputPath(job, output);
boolean status = job.waitForCompletion(true);
return status?0:1;
}
public static void main(String[] args) throws Exception {
int run = new ToolRunner().run(new ScoreOutputFormatMR(), args);
System.exit(run);
}
static class ScoreOutputFormatMRMapper extends Mapper<LongWritable, Text, Text, NullWritable>{
@Override
protected void map(LongWritable key, Text value,
Mapper<LongWritable, Text, Text, NullWritable>.Context context)
throws IOException, InterruptedException {
String[] split = value.toString().split("\t");
if(split.length-2 >= 6){
context.write(new Text("1::"+value.toString()), NullWritable.get());
}else{
context.write(new Text("2::"+value.toString()), NullWritable.get());
}
}
}
}
三、自定义 InputFormat—小文件合并
第一步：自定义InputFormat
package com.ghgj.mr.format.input;
import java.io.IOException;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
public class WholeFileInputFormat extends FileInputFormat<NullWritable, Text> {
// 设置每个小文件不可分片,保证一个小文件生成一个key-value键值对
@Override
protected boolean isSplitable(JobContext context, Path file) {
return false;
}
@Override
public RecordReader<NullWritable, Text> createRecordReader(
InputSplit split, TaskAttemptContext context) throws IOException,
InterruptedException {
WholeFileRecordReader reader = new WholeFileRecordReader();
reader.initialize(split, context);
return reader;
}
}
第二步：编写自定义的 RecordReader
package com.ghgj.mr.format.input;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
class WholeFileRecordReader extends RecordReader<NullWritable, Text> {
private FileSplit fileSplit;
private Configuration conf;
private Text value = new Text();
private boolean processed = false;
@Override
public void initialize(InputSplit split, TaskAttemptContext context)
throws IOException, InterruptedException {
this.fileSplit = (FileSplit) split;
this.conf = context.getConfiguration();
}
@Override
public boolean nextKeyValue() throws IOException, InterruptedException {
if (!processed) {
// 获取 输入逻辑切片的 字节数组
byte[] contents = new byte[(int) fileSplit.getLength()];
// 通过 filesplit获取该逻辑切片在文件系统的位置
Path file = fileSplit.getPath();
FileSystem fs = file.getFileSystem(conf);
FSDataInputStream in = null;
try {
// 文件系统对象fs打开一个file的输入流
in = fs.open(file);
/**
* in是输入流
* contents是存这个流读取的到数的数据的字节数组
*
*/
IOUtils.readFully(in, contents, 0, contents.length);
value.set(contents, 0, contents.length);
} finally {
IOUtils.closeStream(in);
}
processed = true;
return true;
}
return false;
}
@Override
public NullWritable getCurrentKey() throws IOException, InterruptedException {
return NullWritable.get();
}
@Override
public Text getCurrentValue() throws IOException, InterruptedException {
return value;
}
@Override
public float getProgress() throws IOException {
return processed ? 1.0f : 0.0f;
}
@Override
public void close() throws IOException {
// do nothing
}
}
第三步：编写mapreduce程序
package com.ghgj.mr.format.input;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
public class SmallFilesConvertToBigMR extends Configured implements Tool {
public static void main(String[] args) throws Exception {
int exitCode = ToolRunner.run(new SmallFilesConvertToBigMR(), args);
System.exit(exitCode);
}
static class SmallFilesConvertToBigMRMapper extends
Mapper<NullWritable, Text, Text, Text> {
private Text filenameKey;
@Override
protected void setup(Context context) throws IOException,
InterruptedException {
InputSplit split = context.getInputSplit();
Path path = ((FileSplit) split).getPath();
filenameKey = new Text(path.toString());
}
@Override
protected void map(NullWritable key, Text value, Context context)
throws IOException, InterruptedException {
context.write(filenameKey, value);
}
}
static class SmallFilesConvertToBigMRReducer extends
Reducer<Text, Text, NullWritable, Text> {
@Override
protected void reduce(Text filename, Iterable<Text> bytes,
Context context) throws IOException, InterruptedException {
context.write(NullWritable.get(), bytes.iterator().next());
}
}
@Override
public int run(String[] args) throws Exception {
Configuration conf = new Configuration();
conf.set("fs.defaultFS", "hdfs://hadoop02:9000");
System.setProperty("HADOOP_USER_NAME", "hadoop");
Job job = Job.getInstance(conf, "combine small files to bigfile");
job.setJarByClass(SmallFilesConvertToBigMR.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
job.setMapperClass(SmallFilesConvertToBigMRMapper.class);
job.setOutputKeyClass(NullWritable.class);
job.setOutputValueClass(Text.class);
job.setReducerClass(SmallFilesConvertToBigMRReducer.class);
// TextInputFormat是默认的数据读取组件
// job.setInputFormatClass(TextInputFormat.class);
// 不是用默认的读取数据的Format，我使用自定义的 WholeFileInputFormat
job.setInputFormatClass(WholeFileInputFormat.class);
Path input = new Path("/smallfiles");
Path output = new Path("/bigfile");
FileInputFormat.setInputPaths(job, input);
FileSystem fs = FileSystem.get(conf);
if (fs.exists(output)) {
fs.delete(output, true);
}
FileOutputFormat.setOutputPath(job, output);
int status = job.waitForCompletion(true) ? 0 : 1;
return status;
}
}
