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MapReduce 常见SQL模型解析

MapReduce应用场景

前一阵子参加炼数成金的MapReduce培训,培训中的作业例子比较有代表性,用于解释问题再好不过了。有一本国外的有关MR的教材,比较实用,点此下载。

MR能解决什么问题?一般来说,用的最多的应该是日志分析,海量数据排序处理。最近一段时间公司用MR来解决大量日志的离线并行分析问题。

 

MapReduce机制

对于不熟悉MR工作原理的同学,推荐大家先去看一篇博文:http://blog.csdn.net/athenaer/article/details/8203990

 

常用计算模型

这里举一个例子,数据表在Oracle默认用户Scott下有DEPT表和EMP表。为方便,现在直接写成两个TXT文件如下:

1.部门表

DEPTNO,DNAME,LOC    // 部门号,部门名称,所在地

DEPTNO,DNAME,LOC    // 部门号,部门名称,所在地10,ACCOUNTING,NEW YORK  20,RESEARCH,DALLAS  30,SALES,CHICAGO  40,OPERATIONS,BOSTON

 

2.员工表

EMPNO,ENAME,JOB,HIREDATE,SAL,COMM,DEPTNO,MGR // 员工号,英文名,职位,聘期,工资,奖金,所属部门,管理者

7369,SMITH,CLERK,1980-12-17 00:00:00.0,800,,20,7902  7499,ALLEN,SALESMAN,1981-02-20 00:00:00.0,1600,300,30,7698  7521,WARD,SALESMAN,1981-02-22 00:00:00.0,1250,500,30,7698  7566,JONES,MANAGER,1981-04-02 00:00:00.0,2975,,20,7839  7654,MARTIN,SALESMAN,1981-09-28 00:00:00.0,1250,1400,30,7698  7698,BLAKE,MANAGER,1981-05-01 00:00:00.0,2850,,30,7839  7782,CLARK,MANAGER,1981-06-09 00:00:00.0,2450,    ,10,7839  7839,KING,PRESIDENT,1981-11-17 00:00:00.0,5000,,10,  7844,TURNER,SALESMAN,1981-09-08 00:00:00.0,1500,0,30,7698  7900,JAMES,CLERK,1981-12-03 00:00:00.0,950,,30,7698  7902,FORD,ANALYST,1981-12-03 00:00:00.0,3000,,20,7566  7934,MILLER,CLERK,1982-01-23 00:00:00.0,1300,,10,7782

 

3.实例化为bean

这两个bean的实际作用都是分割传入的字符串,从字符串内得到所属的属性信息。

emp.java

public Emp(String inStr) {          String[] split = inStr.split(",");          this.empno = (split[0].isEmpty()? "" : split[0]);          this.ename = (split[1].isEmpty() ? "" : split[1]);          this.job = (split[2].isEmpty() ? "" : split[2]);          this.hiredate = (split[3].isEmpty() ? "" : split[3]);          this.sal = (split[4].isEmpty() ? "0" : split[4]);          this.comm = (split[5].isEmpty() ? "" : split[5]);          this.deptno = (split[6].isEmpty() ? "" : split[6]);          try {              this.mgr = (split[7].isEmpty() ? "" : split[7]);          } catch (IndexOutOfBoundsException e) {     //防止最后一位为空的情况              this.mgr = "";          }  }

 

dep.java

public Dept(String string) {          String[] split = string.split(",");          this.deptno = split[0];          this.dname = split[1];          this.loc = split[2];      }
 
 

4.模型分析

4.1 求和

求各个部门的总工资

public static class Map_1 extends MapReduceBase implements Mapper<Object, Text, Text, IntWritable> {          public void map(Object key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {              try {                  Emp emp = new Emp(value.toString());                  output.collect(new Text(emp.getDeptno()), new IntWritable(Integer.parseInt(emp.getSal())));  // { k=部门号,v=员工薪资}              } catch (Exception e) {              reporter.getCounter(ErrCount.LINESKIP).increment(1);              WriteErrLine.write("./input/" + this.getClass().getSimpleName() + "err_lines", reporter.getCounter(ErrCount.LINESKIP).getCounter() + " " + value.toString());              }          }          }        public static class Reduce_1 extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {          public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {              int sum = 0;              while (values.hasNext()) {                  sum = sum + values.next().get();              }              output.collect(key, new IntWritable(sum));          }        }

运行结果:

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4.2 平均值

求各个部门的人数和平均工资

public static class Map_2 extends MapReduceBase implements Mapper<Object, Text, Text, IntWritable> {          public void map(Object key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {              try {                  Emp emp = new Emp(value.toString());                  output.collect(new Text(emp.getDeptno()), new IntWritable(Integer.parseInt(emp.getSal())));  //{ k=部门号,v=薪资}              } catch (Exception e) {                  reporter.getCounter(ErrCount.LINESKIP).increment(1);                  WriteErrLine.write("./input/" + this.getClass().getSimpleName() + "err_lines", reporter.getCounter(ErrCount.LINESKIP).getCounter() + " " + value.toString());              }            }      }        public static class Reduce_2 extends MapReduceBase implements Reducer<Text, IntWritable, Text, Text> {          public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              double sum = 0; //部门工资              int count =0 ; //人数              while (values.hasNext()) {                  count++;                  sum = sum + values.next().get();              }              output.collect(key, new Text( count+" "+sum/count));          }        }

运行结果

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4.3 分组排序

求每个部门最早进入公司的员工姓名

public static class Map_3 extends MapReduceBase implements Mapper<Object, Text, Text, Text> {      public void map(Object key, Text value, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {          try {              Emp emp = new Emp(value.toString());              output.collect(new Text(emp.getDeptno()), new Text(emp.getHiredate() + "~" + emp.getEname())); // { k=部门号,v=聘期}          } catch (Exception e) {              reporter.getCounter(ErrCount.LINESKIP).increment(1);              WriteErrLine.write("./input/" + this.getClass().getSimpleName() + "err_lines", reporter.getCounter(ErrCount.LINESKIP).getCounter() + " " + value.toString());          }        }  }    public static class Reduce_3 extends MapReduceBase implements Reducer<Text, Text, Text, Text> {      public void reduce(Text key, Iterator<Text> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {          DateFormat sdf = DateFormat.getDateInstance();          Date minDate = new Date(9999, 12, 30);          Date d;          String[] strings = null;          while (values.hasNext()) {              try {                  strings = values.next().toString().split("~"); // 获取名字和日期                  d = sdf.parse(strings[0].toString().substring(0, 10));                  if (d.before(minDate)) {                      minDate = d;                  }              } catch (ParseException e) {                  e.printStackTrace();              }          }          output.collect(key, new Text(minDate.toLocaleString() + " " + strings[1]));        }    }

运行结果

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4.4 多表关联

求各个城市的员工的总工资

public static class Map_4 extends MapReduceBase implements Mapper<Object, Text, Text, Text> {          public void map(Object key, Text value, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              try {                  String fileName = ((FileSplit) reporter.getInputSplit()).getPath().getName();                  if (fileName.equalsIgnoreCase("emp.txt")) {                      Emp emp = new Emp(value.toString());                      output.collect(new Text(emp.getDeptno()), new Text("A#" + emp.getSal()));                  }                  if (fileName.equalsIgnoreCase("dept.txt")) {                      Dept dept = new Dept(value.toString());                      output.collect(new Text(dept.getDeptno()), new Text("B#" + dept.getLoc()));                  }              } catch (Exception e) {                  reporter.getCounter(ErrCount.LINESKIP).increment(1);                  WriteErrLine.write("./input/" + this.getClass().getSimpleName() + "err_lines", reporter.getCounter(ErrCount.LINESKIP).getCounter() + " " + value.toString());              }            }      }        public static class Reduce_4 extends MapReduceBase implements Reducer<Text, Text, Text, Text> {          public void reduce(Text key, Iterator<Text> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              String deptV;              Vector<String> empList = new Vector<String>(); // 保存EMP表的工资数据              Vector<String> deptList = new Vector<String>(); // 保存DEPT表的位置数据              while (values.hasNext()) {                  deptV = values.next().toString();                  if (deptV.startsWith("A#")) {                      empList.add(deptV.substring(2));                  }                  if (deptV.startsWith("B#")) {                      deptList.add(deptV.substring(2));                  }              }              double sumSal = 0;              for (String location : deptList) {                  for (String salary : empList) {                      //每个城市员工工资总和                      sumSal = Integer.parseInt(salary) + sumSal;                  }                  output.collect(new Text(location), new Text(Double.toString(sumSal)));              }          }        }

运行结果

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4.5 单表关联

工资比上司高的员工姓名及其工资

public static class Map_5 extends MapReduceBase implements Mapper<Object, Text, Text, Text> {          public void map(Object key, Text value, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              try {                  Emp emp = new Emp(value.toString());                  output.collect(new Text(emp.getMgr()), new Text("A#" + emp.getEname() + "~" + emp.getSal()));  // 员工表 { k=上司名,v=员工工资}                  output.collect(new Text(emp.getEmpno()), new Text("B#" + emp.getEname() + "~" + emp.getSal()));// “经理表” { k=员工名,v=员工工资}              } catch (Exception e) {                  reporter.getCounter(ErrCount.LINESKIP).increment(1);                  WriteErrLine.write("./input/" + this.getClass().getSimpleName() + "err_lines", reporter.getCounter(ErrCount.LINESKIP).getCounter() + " " + value.toString());              }          }      }        public static class Reduce_5 extends MapReduceBase implements Reducer<Text, Text, Text, Text> {          public void reduce(Text key, Iterator<Text> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              String value;              Vector<String> empList = new Vector<String>(); // 员工表              Vector<String> mgrList = new Vector<String>(); // 经理表              while (values.hasNext()) {                  value = values.next().toString();                  if (value.startsWith("A#")) {                      empList.add(value.substring(2));                  }                  if (value.startsWith("B#")) {                      mgrList.add(value.substring(2));                  }              }              String empName, empSal, mgrSal;                for (String emploee : empList) {                  for (String mgr : mgrList) {                      String[] empInfo = emploee.split("~");                      empName = empInfo[0];                      empSal = empInfo[1];                      String[] mgrInfo = mgr.split("~");                      mgrSal = mgrInfo[1];                      if (Integer.parseInt(empSal) > Integer.parseInt(mgrSal)) {                          output.collect(key, new Text(empName + " " + empSal));                      }                  }              }          }        }

运行结果

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4.6 TOP N

列出工资最高的头三名员工姓名及其工资

public static class Map_8 extends MapReduceBase implements Mapper<Object, Text, Text, Text> {          public void map(Object key, Text value, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              try {                  Emp emp = new Emp(value.toString());                  output.collect(new Text("1"), new Text(emp.getEname() + "~" + emp.getSal()));    // { k=随意字符串或数字,v=员工名字+薪资}              } catch (Exception e) {                  reporter.getCounter(ErrCount.LINESKIP).increment(1);                  WriteErrLine.write("./input/" + this.getClass().getSimpleName() + "err_lines", reporter.getCounter(ErrCount.LINESKIP).getCounter() + " " + value.toString());              }            }      }        public static class Reduce_8 extends MapReduceBase implements Reducer<Text, Text, Text, Text> {          public void reduce(Text key, Iterator<Text> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              Map<Integer, String> emp = new TreeMap<Integer, String>();   // TreeMap默认key升序排列,巧妙利用这点可以实现top N              while (values.hasNext()) {                  String[] valStrings = values.next().toString().split("~");                  emp.put(Integer.parseInt(valStrings[1]), valStrings[0]);              }              int count = 0; // 计数器              for (Iterator<Integer> keySet = emp.keySet().iterator(); keySet.hasNext();) {                  if (count < 3) {  //  N =3                      Integer current_key = keySet.next();                      output.collect(new Text(emp.get(current_key)), new Text(current_key.toString())); // 迭代key,即SAL                      count++;                  } else {                      break;                  }              }          }      }

运算结果

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4.7 降序排序

将全体员工按照总收入(工资+提成)从高到低排列,要求列出姓名及其总收入

public static class Map_9 extends MapReduceBase implements Mapper<Object, Text, Text, Text> {          public void map(Object key, Text value, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              try {                  Emp emp = new Emp(value.toString());                  int totalSal = Integer.parseInt(emp.getComm()) + Integer.parseInt(emp.getSal());                  output.collect(new Text("1"), new Text(emp.getEname() + "~" + totalSal));              } catch (Exception e) {                  reporter.getCounter(ErrCount.LINESKIP).increment(1);                  WriteErrLine.write("./input/" + this.getClass().getSimpleName() + "err_lines", reporter.getCounter(ErrCount.LINESKIP).getCounter() + " " + value.toString());              }            }      }        public static class Reduce_9 extends MapReduceBase implements Reducer<Text, Text, Text, Text> {          public void reduce(Text key, Iterator<Text> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {              Map<Integer, String> emp = new TreeMap<Integer, String>(              // 重写比较器,使降序排列                      new Comparator<Integer>() {                          public int compare(Integer o1, Integer o2) {                              return o2.compareTo(o1);                          }                      });              while (values.hasNext()) {                  String[] valStrings = values.next().toString().split("~");                  emp.put(Integer.parseInt(valStrings[1]), valStrings[0]);              }              for (Iterator<Integer> keySet = emp.keySet().iterator(); keySet.hasNext();) {                  Integer current_key = keySet.next();                  output.collect(new Text(emp.get(current_key)), new Text(current_key.toString())); // 迭代key,即SAL              }          }      }

运行结果

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总结

把sql里常用的计算模型写成MR是一件比较麻烦的事,因为很多情况下一行sql估计要十几甚至几十行代码来实现,略显笨拙。但是从数据计算速度来说,MR跟sql不是一个级别的。

但不可否认的一点是,无论是什么技术都有各自的适用范围,MR不是万能的,具体要看使用场景再选择适当的技术。

MapReduce 常见SQL模型解析