Writing to HDFS from Java, getting “could only be

问题:

I’ve downloaded and started up Cloudera's Hadoop Demo VM for CDH4 (running Hadoop 2.0.0). I’m trying to write a Java program that will run from my windows 7 machine (The same machine/OS that the VM is running in). I have a sample program like:

public static void main(String[] args) {
    try{
        Configuration conf = new Configuration();
        conf.addResource("config.xml");
        FileSystem fs = FileSystem.get(conf);
        FSDataOutputStream fdos=fs.create(new Path("/testing/file01.txt"), true);
        fdos.writeBytes("Test text for the txt file");
        fdos.flush();
        fdos.close();
        fs.close();
    }catch(Exception e){
        e.printStackTrace();
    }

}

My config.xml file only has on property defined: fs.default.name=hdfs://CDH4_IP:8020.

When I run it I’m getting the following exception:

org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /testing/file01.txt could only be replicated to 0 nodes instead of minReplication (=1).  There are 1 datanode(s) running and 1 node(s) are excluded in this operation.
    at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget(BlockManager.java:1322)
    at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2170)
    at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:471)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:297)
    at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java:44080)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:453)
    at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:898)
    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1693)
    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1689)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:396)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1332)
    at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1687)
    at org.apache.hadoop.ipc.Client.call(Client.java:1160)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:202)
    at $Proxy9.addBlock(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:164)
    at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:83)
    at $Proxy9.addBlock(Unknown Source)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:290)
    at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:1150)
    at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1003)
    at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:463)

I’ve looked around the internet and it seem that this happens when disk space is low but that’s not the case for me when I run "hdfs dfsadmin -report" I get the following:

Configured Capacity: 25197727744 (23.47 GB)
Present Capacity: 21771988992 (20.28 GB)
DFS Remaining: 21770715136 (20.28 GB)
DFS Used: 1273856 (1.21 MB)
DFS Used%: 0.01%
Under replicated blocks: 0
Blocks with corrupt replicas: 0
Missing blocks: 0

-------------------------------------------------
Datanodes available: 1 (1 total, 0 dead)

Live datanodes:
Name: 127.0.0.1:50010 (localhost.localdomain)
Hostname: localhost.localdomain
Decommission Status : Normal
Configured Capacity: 25197727744 (23.47 GB)
DFS Used: 1273856 (1.21 MB)
Non DFS Used: 3425738752 (3.19 GB)
DFS Remaining: 21770715136 (20.28 GB)
DFS Used%: 0.01%
DFS Remaining%: 86.4%
Last contact: Fri Jan 11 17:30:56 EST 201323 EST 2013

I can also run this code just fine from with in the VM. I’m not sure what the problem is or how to fix it. This is my first time using hadoop so I’m probably missing something basic. Any ideas?

Update

The only thing I see in the logs is an exception similar to the one on get on the client:

java.io.IOException: File /testing/file01.txt could only be replicated to 0 nodes instead of minReplication (=1).  There are 1 datanode(s) running and 1 node(s) are excluded in this operation.
    at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget(BlockManager.java:1322)
    at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2170)
    at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:471)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:297)
    at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java:44080)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:453)
    at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:898)
    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1693)
    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1689)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:396)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1332)
    at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1687)

I tried changing the permissions on the data directory (/var/lib/hadoop-hdfs/cache/hdfs/dfs/data) and that didn't fix it (I went so far as giving full access to everyone).

I notice that when I'm browsing the HDFS via the HUE web app I see that the folder structure was created and that the file does exist but it is empty. I tried putting the file under the default user directory by using

FSDataOutputStream fdos=fs.create(new Path("testing/file04.txt"), true); 

instead of

FSDataOutputStream fdos=fs.create(new Path("/testing/file04.txt"), true);

Which makes the file path become "/user/dharris/testing/file04.txt" ('dharris' is my windows user). But that gave me the same kind of error.

回答1:

I got a same problem.
In my case, a key of the problem was following error message.
There are 1 datanode(s) running and 1 node(s) are excluded in this operation.

It means that your hdfs-client couldn't connect to your datanode with 50010 port. As you connected to hdfs namenode, you could got a datanode's status. But, your hdfs-client would failed to connect to your datanode.

(In hdfs, a namenode manages file directories, and datanodes. If hdfs-client connect to a namnenode, it will find a target file path and address of datanode that have the data. Then hdfs-client will communicate with datanode. (You can check those datanode uri by using netstat. because, hdfs-client will be trying to communicate with datanodes using by address informed by namenode)

I solved that problem by:

1. opening 50010 port in a firewall.
2. adding propertiy "dfs.client.use.datanode.hostname", "true"
3. adding hostname to hostfile in my client PC.

I'm sorry for my poor English skill.

回答2:

add given property in hdfs-site.xml

<property>
   <name>dfs.replication</name>
   <value>1</value>
 </property>

and add this file also in your program

conf.addResource("hdfs-site.xml");

stop hadoop

stop-all.sh

then start

start-all.sh

回答3:

Go to linux VM and check the hostname and iP ADDRESS(use ifconfig cmd). Then in the linux vm edit /etc/host file with

IPADDRESS (SPALCE) hostname

example : 192.168.110.27 clouderavm

and change the all your hadoop configuration files like

core-site.xml

hdfs-site.xml

mapred-site.xml

yarn-site.xml

change localhost or localhost.localdomain or 0.0.0.0 to your hostname

then Restart cloudera manger.

in the windows machine edit C:\Windows\System32\Drivers\etc\hosts

add one line at the end with

you vm machine ip and hostname (same as you done on the /etc/host file in the vm)

VMIPADRESS VMHOSTNAME

example :

192.168.110.27 clouderavm

then check now, it should work, for detail configuration check following VIDEO from you tube

https://www.youtube.com/watch?v=fSGpYHjGIRY

回答4:

I ran into the similar issue and have two pieces of information may help you.

1. The first thing I realized is I was using ssh tunnel to access the name node and when the client code tries to access data node it can not find the data node due to the tunnel somehow messed up the communication. I then run the client on the same box as the hadoop name node and it solved the problem. In short, non-standard network configuration confused hadoop to find the data node.

2. The reason I used ssh tunnel is I can't access name node remotely and I thought it was due to port restriction by admin, so I used ssh tunnel to bypass the restriction. But it turns out to be a misconfiguration of hadoop.

In core-site.xml after I changed

<name>fs.defaultFS</name>
<value>hdfs://localhost:9000</value>

to

<value>hdfs://host_name:9000</value>

I no longer need the ssh turnnel and I can access the hdfs remotely.

回答5:

Since I found many questions like this one in my search for having the exact same issue I thought I would share what finally worked for me. I found this forum post on Hortonworks: https://community.hortonworks.com/questions/16837/cannot-copy-from-local-machine-to-vm-datanode-via.html

The answer was truly understanding what calling new Configuration() means and setting the correct parameters as I needed them. In my case it was exactly the one mentioned in that post. So my working code looks like this.

try {
    Configuration config = new Configuration();
    config.set("dfs.client.use.datanode.hostname", "true");
    Path pdFile = new Path("stgicp-" + pd);
    FileSystem dFS = FileSystem.get(new URI("hdfs://" + HadoopProperties.HIVE_HOST + ":" + HadoopProperties.HDFS_DEFAULT_PORT), config, 
            HadoopProperties.HIVE_DEFAULT_USER);
    if (dFS.exists(pdFile)) {
        dFS.delete(pdFile, false);
    } 
    FSDataOutputStream outStream = dFS.create(pdFile);
    for (String sjWLR : processWLR.get(pd)) {
        outStream.writeBytes(sjWLR);
    }     
    outStream.flush();
    outStream.close();

    dFS.delete(pdFile, false);
    dFS.close();
} catch (IOException | URISyntaxException | InterruptedException e) {
    log.error("WLR file processing error: " + e.getMessage());
}

回答6:

in the hadoop configuration, default replication is set to 3. check it once and change accordingly to your requirements

回答7:

You can try deleting the data (dfs/data) folder manually and formating the namenode. You can then start hadoop.

回答8:

From error message replication factor seems to be fine i.e.1. It Seems datanode is properly functioning or have permission issues. Check the permissions and check the status of datanode form the user, you are trying to run hadoop.

回答9:

I had a similar problem, in my case I just emptied the following folder ${hadoop.tmp.dir}/nm-local-dir/usercache/{{hdfs_user}}/appcache/

回答10:

It appears to be some issue with the FS. Either the parameters in cross-site.xml are not matching the file it is trying to read

OR

there is some common mismatch in the path (I see there being a WINDOWS reference).

you can use cygwin tool to setup the path and place it where the datanodes and temp file locations are placed and that should sufficiently do the trick Location : $/bin/cygpath.exe

P.S. Replication does NOT seem to be the primary issue here according to me

回答11:

Here is how I create files in the HDFS:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

FileSystem hdfs = FileSystem.get(context.getConfiguration());
Path outFile=new Path("/path to store the output file");

String line1=null;

if (!hdfs.exists(outFile)){
            OutputStream out = hdfs.create(outFile);
            BufferedWriter br = new BufferedWriter(new OutputStreamWriter(out, "UTF-8"));
            br.write("whatever data"+"\n");
            br.close();
            hdfs.close();
        }
else{
            String line2=null;
            BufferedReader br1 = new BufferedReader(new InputStreamReader(hdfs.open(outFile)));
            while((line2=br1.readLine())!=null){
                line1=line1.concat(line2)+"\n";
            }
            br1.close();
            hdfs.delete(outFile, true);
            OutputStream out = hdfs.create(outFile);
            BufferedWriter br2 = new BufferedWriter(new OutputStreamWriter(out, "UTF-8"));
            br2.write(line1+"new data"+"\n");
            br2.close();
            hdfs.close();
        }