当我在小数据上运行代码时，我没有得到以下错误。但是，当我在更大的数据集上运行相同的代码时，在使用多个输出时，我会出现以下错误。请帮忙！
org.apache.hadoop.ipc.RemoteException:
org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException: failed to create file
/home/users/mlakshm/alop176/data-r-00001 for
DFSClient_attempt_201208010142_0043_r_000001_1 on client 10.0.1.100, because this file
is already being created by DFSClient_attempt_201208010142_0043_r_000001_0 on 10.0.1.130 at
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.recoverLeaseInternal(FSNamesystem.java:1406)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFileInternal(FSNamesystem.java:1246)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFile(FSNamesystem.java:1188)
at org.apache.hadoop.hdfs.server.namenode.NameNode.create(NameNode.java:628)
at sun.reflect.GeneratedMethodAccessor12.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:563)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1388)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1384)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:416)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1382)
at org.apache.hadoop.ipc.Client.call(Client.java:1070)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:225)
at $Proxy2.create(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
at $Proxy2.create(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.<init>(DFSClient.java:3248)
at org.apache.hadoop.hdfs.DFSClient.create(DFSClient.java:713)
at org.apache.hadoop.hdfs.DistributedFileSystem.create(DistributedFileSystem.java:182)
at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:555)
at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:455)
at org.apache.hadoop.mapred.TextOutputFormat.getRecordWriter(TextOutputFormat.java:118)
at com.a.MultipleOutputs$InternalFileOutputFormat.getRecordWriter(MultipleOutputs.java:565)
at com.a.MultipleOutputs.getRecordWriter(MultipleOutputs.java:432)
at com.a.MultipleOutputs.getCollector(MultipleOutputs.java:518)
at com.a.MultipleOutputs.getCollector(MultipleOutputs.java:482)
at com.a.ReduceThree1.reduce(ReduceThree1.java:56)
at com.a.ReduceThree1.reduce(ReduceThree1.java:1)
at org.apache.hadoop.mapred.ReduceTask.runOldReducer(ReduceTask.java:519)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:420)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:416)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
网址：org.apache.hadop.mapred.Child.main（Child.java:249）
减少等级如下：
public class ReduceThree1 extends MapReduceBase implements Reducer<Text, Text, Text, Text>{
// @SuppressWarnings("unchecked")
private MultipleOutputs mos;
public void configure(JobConf conf1) {
mos = new MultipleOutputs(conf1);
}
public void reduce (Text key, Iterator<Text> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {
// MultipleOutputs mos;
int sum = 0;
ArrayList<CustomMapI> alcmap = new ArrayList<CustomMapI>();
while(values.hasNext())
{
String val = values.next().toString();
StringTokenizer st = new StringTokenizer(val);
String uid = st.nextToken();
String f_val = st.nextToken();
CustomMapI cmap = new CustomMapI(uid, f_val);
alcmap.add(cmap);
sum += Integer.parseInt(f_val);
}
StringTokenizer st = new StringTokenizer(key.toString());
String t = st.nextToken();
String data = st.nextToken();
for(int i = 0; i<alcmap.size(); i++)
{
String str_key = t+" "+alcmap.get(i).getUid();
String str_val = data+" "+alcmap.get(i).getF_val()+" "+sum;
// output.collect(new Text(str_key), new Text(str_val));
mos.getCollector("/home/users/mlakshm/alop176/data", reporter).collect(new Text(str_key), new Text(str_val));
for(int j = 1; j<alcmap.size(); j++)
{
if((j>i)&&(!alcmap.get(i).equals(alcmap.get(j))))
{
String mul_key = "null";
String uidi = alcmap.get(i).getUid();
String uidj = alcmap.get(j).getUid();
ArrayList<String> alsort = new ArrayList<String>();
alsort.add(uidi);
alsort.add(uidj);
Collections.sort(alsort);
int fi = Integer.parseInt(alcmap.get(i).getF_val());
int fj = Integer.parseInt(alcmap.get(j).getF_val());
String intersection = "null";
if(fi<fj)
{
intersection = String.valueOf(fi);
}
else
{
intersection = String.valueOf(fj);
}
String mul_val = t+" "+alsort.get(0)+" "+alsort.get(1)+" "+intersection;
// System.out.println(mul_key+ " "+mul_val);
mos.getCollector("/home/users/mlakshm/alop177/datepairs", reporter).collect(new Text(mul_key), new Text(mul_val));
}
}
}
}
public void close() throws IOException {
mos.close();
}
}
作业配置如下：
配置config1=新配置（）；
JobConf conf1 = new JobConf(config1, DJob.class);
conf1.setJobName("DJob1");
conf1.setOutputKeyClass(Text.class);
conf1.setOutputValueClass(Text.class);
// conf.setMapOutputValueClass(Text.class);
// conf.setMapOutputKeyClass(Text.class);
// conf.setNumMapTasks(20);
conf.setNumReduceTasks(10);
conf1.setMapperClass(MapThree1.class);
// conf.setCombinerClass(Combiner.class);
conf1.setReducerClass(ReduceThree1.class);
conf1.setPartitionerClass(CustomPartitioner.class);
conf1.setInputFormat(TextInputFormat.class);
conf1.setOutputFormat(TextOutputFormat.class);
// mos = new MultipleOutputs(conf1);
MultipleOutputs.addNamedOutput(conf1, "/home/users/mlakshm/alop176/data", TextOutputFormat.class, LongWritable.class, Text.class);
MultipleOutputs.addNamedOutput(conf1, "/home/users/mlakshm/alop177/datepairs", TextOutputFormat.class, LongWritable.class, Text.class);
FileInputFormat.setInputPaths(conf1, new Path(other_args.get(2)));
FileOutputFormat.setOutputPath(conf1, new Path(other_args.get(3)));
JobClient.runJob(conf1);
您很可能在上进行了推测性执行，reduce任务1的两次不同尝试都试图写入路径/home/users/mlakshm/alop176/data-r-00001。对于较小的任务，这可能会成功，因为它们在hadoop推测性地执行第二次尝试之前完成。
我看到您的MultipleOutputs实现是自定义的（com.a.MultipleOutputs），您应该将所有HDFS数据写入任务工作目录，并在输出提交时让OutputComitter将其移动到最终输出目录。如果可以的话，粘贴代码，我们可以看看。