MaxCompute:MultiJobs example

Prerequisites

Complete the environment configuration for testing, see Getting started.

Preparations

1. Prepare the JAR package of the test program. In this topic, the JAR package is named mapreduce-examples.jar and stored in the bin\data\resources directory in the local installation path of MaxCompute.

2. Prepare test tables and resources for MultiJobs.

   1. Create test tables.

      CREATE TABLE mr_empty (key STRING, value STRING);
      CREATE TABLE mr_multijobs_out (value BIGINT);

   2. Add test resources.

      add table mr_multijobs_out as multijobs_res_table -f;
      
      -- When adding the JAR package for the first time, you can ignore the -f flag.
      add jar data\resources\mapreduce-examples.jar -f;

Procedure

jar -resources mapreduce-examples.jar,multijobs_res_table -classpath data\resources\mapreduce-examples.jar 
 com.aliyun.odps.mapred.open.example.MultiJobs mr_multijobs_out;

Expected result

+------------+
| value      |
+------------+
| 0          |
+------------+

Sample code

For information about Project Object Model (POM) dependencies, see Precautions.

package com.aliyun.odps.mapred.open.example;
import java.io.IOException;
import java.util.Iterator;
import com.aliyun.odps.data.Record;
import com.aliyun.odps.data.TableInfo;
import com.aliyun.odps.mapred.JobClient;
import com.aliyun.odps.mapred.MapperBase;
import com.aliyun.odps.mapred.RunningJob;
import com.aliyun.odps.mapred.TaskContext;
import com.aliyun.odps.mapred.conf.JobConf;
import com.aliyun.odps.mapred.utils.InputUtils;
import com.aliyun.odps.mapred.utils.OutputUtils;
import com.aliyun.odps.mapred.utils.SchemaUtils;
/**
     * MultiJobs
     *
     * Running multiple job
     *
     **/
public class MultiJobs {
    public static class InitMapper extends MapperBase {
        @Override
            public void setup(TaskContext context) throws IOException {
            Record record = context.createOutputRecord();
            long v = context.getJobConf().getLong("multijobs.value", 2);
            record.set(0, v);
            context.write(record);
        }
    }
    public static class DecreaseMapper extends MapperBase {
        @Override
            public void cleanup(TaskContext context) throws IOException {
            /** Obtain the variable values that are defined in the main function from JobConf. */
            long expect = context.getJobConf().getLong("multijobs.expect.value", -1);
            long v = -1;
            int count = 0;
            /** Read the data from the output table of the previous job. */
            Iterator<Record> iter = context.readResourceTable("multijobs_res_table");
            while (iter.hasNext()) {
                Record r = iter.next();
                v = (Long) r.get(0);
                if (expect != v) {
                    throw new IOException("expect: " + expect + ", but: " + v);
                }
                count++;
            }
            if (count != 1) {
                throw new IOException("res_table should have 1 record, but: " + count);
            }
            Record record = context.createOutputRecord();
            v--;
            record.set(0, v);
            context.write(record);
            /** Set the counter. The counter value can be obtained in the main function after the job is completed. */
            context.getCounter("multijobs", "value").setValue(v);
        }
    }
    public static void main(String[] args) throws Exception {
        if (args.length != 1) {
            System.err.println("Usage: TestMultiJobs <table>");
            System.exit(1);
        }
        String tbl = args[0];
        long iterCount = 2;
        System.err.println("Start to run init job.");
        JobConf initJob = new JobConf();
        initJob.setLong("multijobs.value", iterCount);
        initJob.setMapperClass(InitMapper.class);
        InputUtils.addTable(TableInfo.builder().tableName("mr_empty").build(), initJob);
        OutputUtils.addTable(TableInfo.builder().tableName(tbl).build(), initJob);
        initJob.setMapOutputKeySchema(SchemaUtils.fromString("key:string"));
        initJob.setMapOutputValueSchema(SchemaUtils.fromString("value:string"));
        /** Explicitly set the number of reducers to 0 for map-only jobs. */
        initJob.setNumReduceTasks(0);
        JobClient.runJob(initJob);
        while (true) {
            System.err.println("Start to run iter job, count: " + iterCount);
            JobConf decJob = new JobConf();
            decJob.setLong("multijobs.expect.value", iterCount);
            decJob.setMapperClass(DecreaseMapper.class);
            InputUtils.addTable(TableInfo.builder().tableName("mr_empty").build(), decJob);
            OutputUtils.addTable(TableInfo.builder().tableName(tbl).build(), decJob);
            /** Explicitly set the number of reducers to 0 for map-only jobs. */
            decJob.setNumReduceTasks(0);
            RunningJob rJob = JobClient.runJob(decJob);
            iterCount--;
            /** If the specified number of iterations is reached, exit the loop. */
            if (rJob.getCounters().findCounter("multijobs", "value").getValue() == 0) {
                break;
            }
        }
        if (iterCount != 0) {
            throw new IOException("Job failed.");
        }
    }
}