Not able to append to existing file to HDFS - hadoop

Question

I have single node Hadoop 1.2.1 cluster running on VM.
My hdfs-site.xml looks like this:
<configuration>
<property>
<name>dfs.replication</name>
<value>1</value>
<description>Default block replication.
</description>
</property>
<property>
<name>dfs.support.append</name>
<value>true</value>
<description>Does HDFS allow appends to files?
</description>
</property>
</configuration>
Now when I'm trying to run the following code from Eclipse it returns me always false:
Configuration config = new Configuration();
config.set("mapred.job.tracker","10.0.0.6:54311");
config.set("fs.default.name","hdfs://10.0.0.6:54310");
FileSystem fs = FileSystem.get(config);
boolean flag = Boolean.getBoolean(fs.getConf().get("dfs.support.append"));
System.out.println("dfs.support.append is set to be " + flag);
Now If I'm trying to append to existing file I'll get the following error:
org.apache.hadoop.ipc.RemoteException: java.io.IOException: Append is not supported. Please see the dfs.support.append configuration parameter
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.appendFile(FSNamesystem.java:1781)
at org.apache.hadoop.hdfs.server.namenode.NameNode.append(NameNode.java:725)
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:606)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:587)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1432)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1428)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1426)
at org.apache.hadoop.ipc.Client.call(Client.java:1113)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:229)
at com.sun.proxy.$Proxy1.append(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:606)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:85)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:62)
at com.sun.proxy.$Proxy1.append(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:933)
at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:922)
at org.apache.hadoop.hdfs.DistributedFileSystem.append(DistributedFileSystem.java:196)
at org.apache.hadoop.fs.FileSystem.append(FileSystem.java:659)
at com.vanilla.hadoop.AppendToHdfsFile.main(AppendToHdfsFile.java:29)
What is wrong? Am I missing something?

Answer 1

You should try with a 2.X.X version or 0.2X version because appending a file on hdfs after hadoop 0.20.2. See more information at here and here

Answer 2

Append is not supported since 1.0.3. Anyway, if you really need the previous functionality, to turn on the append functionality set the flag "dfs.support.broken.append" to true.
hadoop.apache.org/docs/r1.2.1/releasenotes.html

Answer 3

Let's now start with configuring the file system:
public FileSystem configureFileSystem(String coreSitePath, String hdfsSitePath) {
FileSystem fileSystem = null;
try {
Configuration conf = new Configuration();
conf.setBoolean("dfs.support.append", true);
Path coreSite = new Path(coreSitePath);
Path hdfsSite = new Path(hdfsSitePath);
conf.addResource(coreSite);
conf.addResource(hdfsSite);
fileSystem = FileSystem.get(conf);
} catch (IOException ex) {
System.out.println("Error occurred while configuring FileSystem");
}
return fileSystem;
}
Make sure that the property dfs.support.append in hdfs-site.xml is set to true.
You can either set it manually by editing the hdfs-site.xml file or programmatically using:
conf.setBoolean("dfs.support.append", true);
Let's start with appending to a file in HDFS.
public String appendToFile(FileSystem fileSystem, String content, String dest) throws IOException {
Path destPath = new Path(dest);
if (!fileSystem.exists(destPath)) {
System.err.println("File doesn't exist");
return "Failure";
}
Boolean isAppendable = Boolean.valueOf(fileSystem.getConf().get("dfs.support.append"));
if(isAppendable) {
FSDataOutputStream fs_append = fileSystem.append(destPath);
PrintWriter writer = new PrintWriter(fs_append);
writer.append(content);
writer.flush();
fs_append.hflush();
writer.close();
fs_append.close();
return "Success";
}
else {
System.err.println("Please set the dfs.support.append property to true");
return "Failure";
}
}
To see whether the data has been correctly written to HDFS, let's write a method to read from HDFS and return the content as a String.
public String readFromHdfs(FileSystem fileSystem, String hdfsFilePath) {
Path hdfsPath = new Path(hdfsFilePath);
StringBuilder fileContent = new StringBuilder("");
try{
BufferedReader bfr=new BufferedReader(new InputStreamReader(fileSystem.open(hdfsPath)));
String str;
while ((str = bfr.readLine()) != null) {
fileContent.append(str+"\n");
}
}
catch (IOException ex){
System.out.println("----------Could not read from HDFS---------\n");
}
return fileContent.toString();
}
After that, we have successfully written and read the file in HDFS. It's time to close the file system.
public void closeFileSystem(FileSystem fileSystem){
try {
fileSystem.close();
}
catch (IOException ex){
System.out.println("----------Could not close the FileSystem----------");
}
}
Before executing the code, you should have Hadoop running on your system.
You just need to go to HADOOP_HOME and run following command:
./sbin/start-all.sh
For Complete Reference use https://github.com/ksimar/HDFS_AppendAPI