Hadoop 2.2.0 Job源代码阅读笔记
2024-08-29 11:31:18
本文所有涉及的内容均为2.2.0版本中呈现。
概述：
Job在创建Job并且提交的人的眼中，可以在创建的时候通过配置Job的内容，控制Job的执行，以及查询Job的运行状态。一旦Job提交以后，将不能对其进行配置，否则将会出现IllegalStateException异常。
正常情况下用户通过Job类来创建、描述、提交Job，以及监控Job的处理过程。下面是一个简单的例子：
// Create a new Job
Job job = new Job(new Configuration());
job.setJarByClass(MyJob.class); // Specify various job-specific parameters
job.setJobName("myjob"); job.setInputPath(new Path("in"));
job.setOutputPath(new Path("out")); job.setMapperClass(MyJob.MyMapper.class);
job.setReducerClass(MyJob.MyReducer.class);
// Submit the job, then poll for progress until the job is complete
job.waitForCompletion(true);
基本结构：
Job类在org.apache.hadoop.mapreduce包中，继承了JobContextImpl类以及实现了JobContext接口。
Job定义的静态常量：
private static final Log LOG = LogFactory.getLog(Job.class); @InterfaceStability.Evolving
public static enum JobState {DEFINE, RUNNING};
private static final long MAX_JOBSTATUS_AGE = 1000 * 2;
public static final String OUTPUT_FILTER = "mapreduce.client.output.filter";
/** Key in mapred-*.xml that sets completionPollInvervalMillis */
public static final String COMPLETION_POLL_INTERVAL_KEY =
"mapreduce.client.completion.pollinterval"; /** Default completionPollIntervalMillis is 5000 ms. */
static final int DEFAULT_COMPLETION_POLL_INTERVAL = 5000;
/** Key in mapred-*.xml that sets progMonitorPollIntervalMillis */
public static final String PROGRESS_MONITOR_POLL_INTERVAL_KEY =
"mapreduce.client.progressmonitor.pollinterval";
/** Default progMonitorPollIntervalMillis is 1000 ms. */
static final int DEFAULT_MONITOR_POLL_INTERVAL = 1000; public static final String USED_GENERIC_PARSER =
"mapreduce.client.genericoptionsparser.used";
public static final String SUBMIT_REPLICATION =
"mapreduce.client.submit.file.replication";
private static final String TASKLOG_PULL_TIMEOUT_KEY =
"mapreduce.client.tasklog.timeout";
private static final int DEFAULT_TASKLOG_TIMEOUT = 60000;
Job定义的私有变量：
private JobState state = JobState.DEFINE;
private JobStatus status;
private long statustime;
private Cluster cluster;
Job类加载的时候就要执行的加载配置文件的方法：
static {
ConfigUtil.loadResources();
}
加载的配置文件包括mapred-default.xml、mapred-site.xml、yarn-default.xml、yarn-site.xml。
Job的构造函数：
@Deprecated
public Job() throws IOException {
this(new Configuration());
} @Deprecated
public Job(Configuration conf) throws IOException {
this(new JobConf(conf));
} @Deprecated
public Job(Configuration conf, String jobName) throws IOException {
this(conf);
setJobName(jobName);
} Job(JobConf conf) throws IOException {
super(conf, null);
// propagate existing user credentials to job
this.credentials.mergeAll(this.ugi.getCredentials());
this.cluster = null;
} Job(JobStatus status, JobConf conf) throws IOException {
this(conf);
setJobID(status.getJobID());
this.status = status;
state = JobState.RUNNING;
}
可以注意到Hadoop不鼓励通过缺省的构造函数和通过Configuration类来构造Job对象。通过JobConf对象来构建Job是一个不错的选择。
获取Job对象的实例化方法：
除了通过构造函数，Job类中还提供了通过一些静态方法来获取Job的事例对象，看一下具体定义：
/**
* Creates a new {@link Job} with no particular {@link Cluster} .
* A Cluster will be created with a generic {@link Configuration}.
*
* @return the {@link Job} , with no connection to a cluster yet.
* @throws IOException
*/
public static Job getInstance() throws IOException {
// create with a null Cluster
return getInstance(new Configuration());
} /**
* Creates a new {@link Job} with no particular {@link Cluster} and a
* given {@link Configuration}.
*
* The <code>Job</code> makes a copy of the <code>Configuration</code> so
* that any necessary internal modifications do not reflect on the incoming
* parameter.
*
* A Cluster will be created from the conf parameter only when it's needed.
*
* @param conf the configuration
* @return the {@link Job} , with no connection to a cluster yet.
* @throws IOException
*/
public static Job getInstance(Configuration conf) throws IOException {
// create with a null Cluster
JobConf jobConf = new JobConf(conf);
return new Job(jobConf);
} /**
* Creates a new {@link Job} with no particular {@link Cluster} and a given jobName.
* A Cluster will be created from the conf parameter only when it's needed.
*
* The <code>Job</code> makes a copy of the <code>Configuration</code> so
* that any necessary internal modifications do not reflect on the incoming
* parameter.
*
* @param conf the configuration
* @return the {@link Job} , with no connection to a cluster yet.
* @throws IOException
*/
public static Job getInstance(Configuration conf, String jobName)
throws IOException {
// create with a null Cluster
Job result = getInstance(conf);
result.setJobName(jobName);
return result;
} /**
* Creates a new {@link Job} with no particular {@link Cluster} and given
* {@link Configuration} and {@link JobStatus}.
* A Cluster will be created from the conf parameter only when it's needed.
*
* The <code>Job</code> makes a copy of the <code>Configuration</code> so
* that any necessary internal modifications do not reflect on the incoming
* parameter.
*
* @param status job status
* @param conf job configuration
* @return the {@link Job} , with no connection to a cluster yet.
* @throws IOException
*/
public static Job getInstance(JobStatus status, Configuration conf)
throws IOException {
return new Job(status, new JobConf(conf));
} /**
* Creates a new {@link Job} with no particular {@link Cluster}.
* A Cluster will be created from the conf parameter only when it's needed.
*
* The <code>Job</code> makes a copy of the <code>Configuration</code> so
* that any necessary internal modifications do not reflect on the incoming
* parameter.
*
* @param ignored
* @return the {@link Job} , with no connection to a cluster yet.
* @throws IOException
* @deprecated Use {@link #getInstance()}
*/
@Deprecated
public static Job getInstance(Cluster ignored) throws IOException {
return getInstance();
} /**
* Creates a new {@link Job} with no particular {@link Cluster} and given
* {@link Configuration}.
* A Cluster will be created from the conf parameter only when it's needed.
*
* The <code>Job</code> makes a copy of the <code>Configuration</code> so
* that any necessary internal modifications do not reflect on the incoming
* parameter.
*
* @param ignored
* @param conf job configuration
* @return the {@link Job} , with no connection to a cluster yet.
* @throws IOException
* @deprecated Use {@link #getInstance(Configuration)}
*/
@Deprecated
public static Job getInstance(Cluster ignored, Configuration conf)
throws IOException {
return getInstance(conf);
} /**
* Creates a new {@link Job} with no particular {@link Cluster} and given
* {@link Configuration} and {@link JobStatus}.
* A Cluster will be created from the conf parameter only when it's needed.
*
* The <code>Job</code> makes a copy of the <code>Configuration</code> so
* that any necessary internal modifications do not reflect on the incoming
* parameter.
*
* @param cluster cluster
* @param status job status
* @param conf job configuration
* @return the {@link Job} , with no connection to a cluster yet.
* @throws IOException
*/
@Private
public static Job getInstance(Cluster cluster, JobStatus status,
Configuration conf) throws IOException {
Job job = getInstance(status, conf);
job.setCluster(cluster);
return job;
}
可见通过这种方式获取Job实例的时候会有可能涉及到Cluster。
轮询周期的方法：
/** The interval at which monitorAndPrintJob() prints status */
public static int getProgressPollInterval(Configuration conf) {
// Read progress monitor poll interval from config. Default is 1 second.
int progMonitorPollIntervalMillis = conf.getInt(
PROGRESS_MONITOR_POLL_INTERVAL_KEY, DEFAULT_MONITOR_POLL_INTERVAL);
if (progMonitorPollIntervalMillis < 1) {
LOG.warn(PROGRESS_MONITOR_POLL_INTERVAL_KEY +
" has been set to an invalid value; "
+ " replacing with " + DEFAULT_MONITOR_POLL_INTERVAL);
progMonitorPollIntervalMillis = DEFAULT_MONITOR_POLL_INTERVAL;
}
return progMonitorPollIntervalMillis;
} /** The interval at which waitForCompletion() should check. */
public static int getCompletionPollInterval(Configuration conf) {
int completionPollIntervalMillis = conf.getInt(
COMPLETION_POLL_INTERVAL_KEY, DEFAULT_COMPLETION_POLL_INTERVAL);
if (completionPollIntervalMillis < 1) {
LOG.warn(COMPLETION_POLL_INTERVAL_KEY +
" has been set to an invalid value; "
+ "replacing with " + DEFAULT_COMPLETION_POLL_INTERVAL);
completionPollIntervalMillis = DEFAULT_COMPLETION_POLL_INTERVAL;
}
return completionPollIntervalMillis;
}
上面两个方法分别为获取并且打印Job的运行状态的周期，以及查看Job是否完成的周期。
需要做异步处理的方法：
synchronized void ensureFreshStatus()
throws IOException {
if (System.currentTimeMillis() - statustime > MAX_JOBSTATUS_AGE) {
updateStatus();
}
} /** Some methods need to update status immediately. So, refresh
* immediately
* @throws IOException
*/
synchronized void updateStatus() throws IOException {
try {
this.status = ugi.doAs(new PrivilegedExceptionAction<JobStatus>() {
@Override
public JobStatus run() throws IOException, InterruptedException {
return cluster.getClient().getJobStatus(status.getJobID());
}
});
}
catch (InterruptedException ie) {
throw new IOException(ie);
}
if (this.status == null) {
throw new IOException("Job status not available ");
}
this.statustime = System.currentTimeMillis();
} private synchronized void connect()
throws IOException, InterruptedException, ClassNotFoundException {
if (cluster == null) {
cluster =
ugi.doAs(new PrivilegedExceptionAction<Cluster>() {
public Cluster run()
throws IOException, InterruptedException,
ClassNotFoundException {
return new Cluster(getConfiguration());
}
});
}
}
设置配置参数的方法：
/**
* Set the number of reduce tasks for the job.
* @param tasks the number of reduce tasks
* @throws IllegalStateException if the job is submitted
*/
public void setNumReduceTasks(int tasks) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setNumReduceTasks(tasks);
} /**
* Set the current working directory for the default file system.
*
* @param dir the new current working directory.
* @throws IllegalStateException if the job is submitted
*/
public void setWorkingDirectory(Path dir) throws IOException {
ensureState(JobState.DEFINE);
conf.setWorkingDirectory(dir);
} /**
* Set the {@link InputFormat} for the job.
* @param cls the <code>InputFormat</code> to use
* @throws IllegalStateException if the job is submitted
*/
public void setInputFormatClass(Class<? extends InputFormat> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setClass(INPUT_FORMAT_CLASS_ATTR, cls,
InputFormat.class);
} /**
* Set the {@link OutputFormat} for the job.
* @param cls the <code>OutputFormat</code> to use
* @throws IllegalStateException if the job is submitted
*/
public void setOutputFormatClass(Class<? extends OutputFormat> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setClass(OUTPUT_FORMAT_CLASS_ATTR, cls,
OutputFormat.class);
} /**
* Set the {@link Mapper} for the job.
* @param cls the <code>Mapper</code> to use
* @throws IllegalStateException if the job is submitted
*/
public void setMapperClass(Class<? extends Mapper> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setClass(MAP_CLASS_ATTR, cls, Mapper.class);
} /**
* Set the Jar by finding where a given class came from.
* @param cls the example class
*/
public void setJarByClass(Class<?> cls) {
ensureState(JobState.DEFINE);
conf.setJarByClass(cls);
} /**
* Set the job jar
*/
public void setJar(String jar) {
ensureState(JobState.DEFINE);
conf.setJar(jar);
} /**
* Set the reported username for this job.
*
* @param user the username for this job.
*/
public void setUser(String user) {
ensureState(JobState.DEFINE);
conf.setUser(user);
} /**
* Set the combiner class for the job.
* @param cls the combiner to use
* @throws IllegalStateException if the job is submitted
*/
public void setCombinerClass(Class<? extends Reducer> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setClass(COMBINE_CLASS_ATTR, cls, Reducer.class);
} /**
* Set the {@link Reducer} for the job.
* @param cls the <code>Reducer</code> to use
* @throws IllegalStateException if the job is submitted
*/
public void setReducerClass(Class<? extends Reducer> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setClass(REDUCE_CLASS_ATTR, cls, Reducer.class);
} /**
* Set the {@link Partitioner} for the job.
* @param cls the <code>Partitioner</code> to use
* @throws IllegalStateException if the job is submitted
*/
public void setPartitionerClass(Class<? extends Partitioner> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setClass(PARTITIONER_CLASS_ATTR, cls,
Partitioner.class);
} /**
* Set the key class for the map output data. This allows the user to
* specify the map output key class to be different than the final output
* value class.
*
* @param theClass the map output key class.
* @throws IllegalStateException if the job is submitted
*/
public void setMapOutputKeyClass(Class<?> theClass
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setMapOutputKeyClass(theClass);
} /**
* Set the value class for the map output data. This allows the user to
* specify the map output value class to be different than the final output
* value class.
*
* @param theClass the map output value class.
* @throws IllegalStateException if the job is submitted
*/
public void setMapOutputValueClass(Class<?> theClass
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setMapOutputValueClass(theClass);
} /**
* Set the key class for the job output data.
*
* @param theClass the key class for the job output data.
* @throws IllegalStateException if the job is submitted
*/
public void setOutputKeyClass(Class<?> theClass
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setOutputKeyClass(theClass);
} /**
* Set the value class for job outputs.
*
* @param theClass the value class for job outputs.
* @throws IllegalStateException if the job is submitted
*/
public void setOutputValueClass(Class<?> theClass
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setOutputValueClass(theClass);
} /**
* Define the comparator that controls how the keys are sorted before they
* are passed to the {@link Reducer}.
* @param cls the raw comparator
* @throws IllegalStateException if the job is submitted
*/
public void setSortComparatorClass(Class<? extends RawComparator> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setOutputKeyComparatorClass(cls);
} /**
* Define the comparator that controls which keys are grouped together
* for a single call to
* {@link Reducer#reduce(Object, Iterable,
* org.apache.hadoop.mapreduce.Reducer.Context)}
* @param cls the raw comparator to use
* @throws IllegalStateException if the job is submitted
*/
public void setGroupingComparatorClass(Class<? extends RawComparator> cls
) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setOutputValueGroupingComparator(cls);
} /**
* Set the user-specified job name.
*
* @param name the job's new name.
* @throws IllegalStateException if the job is submitted
*/
public void setJobName(String name) throws IllegalStateException {
ensureState(JobState.DEFINE);
conf.setJobName(name);
} /**
* Turn speculative execution on or off for this job.
*
* @param speculativeExecution <code>true</code> if speculative execution
* should be turned on, else <code>false</code>.
*/
public void setSpeculativeExecution(boolean speculativeExecution) {
ensureState(JobState.DEFINE);
conf.setSpeculativeExecution(speculativeExecution);
} /**
* Turn speculative execution on or off for this job for map tasks.
*
* @param speculativeExecution <code>true</code> if speculative execution
* should be turned on for map tasks,
* else <code>false</code>.
*/
public void setMapSpeculativeExecution(boolean speculativeExecution) {
ensureState(JobState.DEFINE);
conf.setMapSpeculativeExecution(speculativeExecution);
} /**
* Turn speculative execution on or off for this job for reduce tasks.
*
* @param speculativeExecution <code>true</code> if speculative execution
* should be turned on for reduce tasks,
* else <code>false</code>.
*/
public void setReduceSpeculativeExecution(boolean speculativeExecution) {
ensureState(JobState.DEFINE);
conf.setReduceSpeculativeExecution(speculativeExecution);
} /**
* Specify whether job-setup and job-cleanup is needed for the job
*
* @param needed If <code>true</code>, job-setup and job-cleanup will be
* considered from {@link OutputCommitter}
* else ignored.
*/
public void setJobSetupCleanupNeeded(boolean needed) {
ensureState(JobState.DEFINE);
conf.setBoolean(SETUP_CLEANUP_NEEDED, needed);
} /**
* Set the given set of archives
* @param archives The list of archives that need to be localized
*/
public void setCacheArchives(URI[] archives) {
ensureState(JobState.DEFINE);
DistributedCache.setCacheArchives(archives, conf);
} /**
* Set the given set of files
* @param files The list of files that need to be localized
*/
public void setCacheFiles(URI[] files) {
ensureState(JobState.DEFINE);
DistributedCache.setCacheFiles(files, conf);
} /**
* Add a archives to be localized
* @param uri The uri of the cache to be localized
*/
public void addCacheArchive(URI uri) {
ensureState(JobState.DEFINE);
DistributedCache.addCacheArchive(uri, conf);
} /**
* Add a file to be localized
* @param uri The uri of the cache to be localized
*/
public void addCacheFile(URI uri) {
ensureState(JobState.DEFINE);
DistributedCache.addCacheFile(uri, conf);
} /**
* Add an file path to the current set of classpath entries It adds the file
* to cache as well.
*
* Files added with this method will not be unpacked while being added to the
* classpath.
* To add archives to classpath, use the {@link #addArchiveToClassPath(Path)}
* method instead.
*
* @param file Path of the file to be added
*/
public void addFileToClassPath(Path file)
throws IOException {
ensureState(JobState.DEFINE);
DistributedCache.addFileToClassPath(file, conf, file.getFileSystem(conf));
} /**
* Add an archive path to the current set of classpath entries. It adds the
* archive to cache as well.
*
* Archive files will be unpacked and added to the classpath
* when being distributed.
*
* @param archive Path of the archive to be added
*/
public void addArchiveToClassPath(Path archive)
throws IOException {
ensureState(JobState.DEFINE);
DistributedCache.addArchiveToClassPath(archive, conf, archive.getFileSystem(conf));
} /**
* Originally intended to enable symlinks, but currently symlinks cannot be
* disabled.
*/
@Deprecated
public void createSymlink() {
ensureState(JobState.DEFINE);
DistributedCache.createSymlink(conf);
} /**
* Expert: Set the number of maximum attempts that will be made to run a
* map task.
*
* @param n the number of attempts per map task.
*/
public void setMaxMapAttempts(int n) {
ensureState(JobState.DEFINE);
conf.setMaxMapAttempts(n);
} /**
* Expert: Set the number of maximum attempts that will be made to run a
* reduce task.
*
* @param n the number of attempts per reduce task.
*/
public void setMaxReduceAttempts(int n) {
ensureState(JobState.DEFINE);
conf.setMaxReduceAttempts(n);
} /**
* Set whether the system should collect profiler information for some of
* the tasks in this job? The information is stored in the user log
* directory.
* @param newValue true means it should be gathered
*/
public void setProfileEnabled(boolean newValue) {
ensureState(JobState.DEFINE);
conf.setProfileEnabled(newValue);
} /**
* Set the profiler configuration arguments. If the string contains a '%s' it
* will be replaced with the name of the profiling output file when the task
* runs.
*
* This value is passed to the task child JVM on the command line.
*
* @param value the configuration string
*/
public void setProfileParams(String value) {
ensureState(JobState.DEFINE);
conf.setProfileParams(value);
} /**
* Set the ranges of maps or reduces to profile. setProfileEnabled(true)
* must also be called.
* @param newValue a set of integer ranges of the map ids
*/
public void setProfileTaskRange(boolean isMap, String newValue) {
ensureState(JobState.DEFINE);
conf.setProfileTaskRange(isMap, newValue);
} /**
* Sets the flag that will allow the JobTracker to cancel the HDFS delegation
* tokens upon job completion. Defaults to true.
*/
public void setCancelDelegationTokenUponJobCompletion(boolean value) {
ensureState(JobState.DEFINE);
conf.setBoolean(JOB_CANCEL_DELEGATION_TOKEN, value);
}
要非常注意的地方就是在每项配置的时候都需要检查状态，Job只有处于DEFINE状态下的时候才可以对其进行配置。
屏幕输出的方法：
/**
* Dump stats to screen.
*/
@Override
public String toString() {
ensureState(JobState.RUNNING);
String reasonforFailure = " ";
int numMaps = 0;
int numReduces = 0;
try {
updateStatus();
if (status.getState().equals(JobStatus.State.FAILED))
reasonforFailure = getTaskFailureEventString();
numMaps = getTaskReports(TaskType.MAP).length;
numReduces = getTaskReports(TaskType.REDUCE).length;
} catch (IOException e) {
} catch (InterruptedException ie) {
}
StringBuffer sb = new StringBuffer();
sb.append("Job: ").append(status.getJobID()).append("\n");
sb.append("Job File: ").append(status.getJobFile()).append("\n");
sb.append("Job Tracking URL : ").append(status.getTrackingUrl());
sb.append("\n");
sb.append("Uber job : ").append(status.isUber()).append("\n");
sb.append("Number of maps: ").append(numMaps).append("\n");
sb.append("Number of reduces: ").append(numReduces).append("\n");
sb.append("map() completion: ");
sb.append(status.getMapProgress()).append("\n");
sb.append("reduce() completion: ");
sb.append(status.getReduceProgress()).append("\n");
sb.append("Job state: ");
sb.append(status.getState()).append("\n");
sb.append("retired: ").append(status.isRetired()).append("\n");
sb.append("reason for failure: ").append(reasonforFailure);
return sb.toString();
}
获取任务进程的方法：
/**
* Get the <i>progress</i> of the job's map-tasks, as a float between 0.0
* and 1.0. When all map tasks have completed, the function returns 1.0.
*
* @return the progress of the job's map-tasks.
* @throws IOException
*/
public float mapProgress() throws IOException {
ensureState(JobState.RUNNING);
ensureFreshStatus();
return status.getMapProgress();
} /**
* Get the <i>progress</i> of the job's reduce-tasks, as a float between 0.0
* and 1.0. When all reduce tasks have completed, the function returns 1.0.
*
* @return the progress of the job's reduce-tasks.
* @throws IOException
*/
public float reduceProgress() throws IOException {
ensureState(JobState.RUNNING);
ensureFreshStatus();
return status.getReduceProgress();
} /**
* Get the <i>progress</i> of the job's cleanup-tasks, as a float between 0.0
* and 1.0. When all cleanup tasks have completed, the function returns 1.0.
*
* @return the progress of the job's cleanup-tasks.
* @throws IOException
*/
public float cleanupProgress() throws IOException, InterruptedException {
ensureState(JobState.RUNNING);
ensureFreshStatus();
return status.getCleanupProgress();
} /**
* Get the <i>progress</i> of the job's setup-tasks, as a float between 0.0
* and 1.0. When all setup tasks have completed, the function returns 1.0.
*
* @return the progress of the job's setup-tasks.
* @throws IOException
*/
public float setupProgress() throws IOException {
ensureState(JobState.RUNNING);
ensureFreshStatus();
return status.getSetupProgress();
}
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