java - hadoop2.2.0追加文件出现AlreadyBeingCreatedException

Question

我遇到了一个关于hadoop2.2.0追加操作的问题。我通过 HDFS java API 将一些字节 append 到 hdfs 文件。首先，如果文件在 append 操作之前不存在，我将创建目标文件，代码如下:

String fileUri = "hdfs://hadoopmaster:9000/in/append_test.txt";
// create the hdfs file, if not exists
HdfsClient.createPathIfNotExist(fileUri);
// do 5 times append operation
for (int i=0; i<5; i++){
    HdfsClient.appendTo(fileUri, ("append content"+i).getBytes("UTF-8"));
}

createPathIfNotExist 函数:

Path p = null;
FileSystem fs = null;
try {
    fs = FileSystem.get(URI.create(uri), conf);
    p = new Path(uri);
    if (!fs.exists(p)) {
    if (uri.charAt(uri.length() - 1) == '/'){ //create a directory
        if(fs.mkdirs(p)){
               // create successfully
            }
        }else{ //create a file
        FSDataOutputStream fos = fs.create(p);
            fos.close();
        }
    } else{
        System.out.println(uri + "existing");
    }
} catch (IOException e) {
    e.printStackTrace();
} finally{
    if (fs != null)
    try {
       fs.close();
       fs = null;
    } catch (IOException e) {
       e.printStackTrace();
        }
}

appendTo 函数:

ByteArrayInputStream in = null;
OutputStream out = null;
FileSystem fs = null;
try {
   in = new ByteArrayInputStream(bytes);
   fs = FileSystem.get(URI.create(uri), conf);
   out = fs.append(new Path(uri)); //get append outputstream
   IOUtils.copyBytes(in, out, bufferSize, false);
} catch(Exception e){
   e.printStackTrace();
} finally{
   if (in != null) IOUtils.closeStream(in);
   if (out != null) IOUtils.closeStream(out);
   if (fs != null){
    try {
           fs.close();
           fs = null;
    } catch (IOException e) {
       e.printStackTrace();
    }
   }
}

结果是创建了append_test.txt，但是内容只有:

append content0

并发生异常:

org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException): Failed to create file [/in/append_test.txt] for [DFSClient_NONMAPREDUCE_-1148656837_1] on client [192.168.141.1], because this file is already being created by [DFSClient_NONMAPREDUCE_2099912242_1] on [192.168.141.1]
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.recoverLeaseInternal(FSNamesystem.java:2320)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.appendFileInternal(FSNamesystem.java:2153)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.appendFileInt(FSNamesystem.java:2386)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.appendFile(FSNamesystem.java:2347)
        at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.append(NameNodeRpcServer.java:508)
        at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.append(ClientNamenodeProtocolServerSideTranslatorPB.java:320)
        at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java:59572)
        at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:585)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:928)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2048)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2044)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:415)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1491)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2042)

        at org.apache.hadoop.ipc.Client.call(Client.java:1347)
        at org.apache.hadoop.ipc.Client.call(Client.java:1300)
        at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:206)
        at com.sun.proxy.$Proxy10.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:186)
        at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:102)
        at com.sun.proxy.$Proxy10.append(Unknown Source)
        at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.append(ClientNamenodeProtocolTranslatorPB.java:245)
        at org.apache.hadoop.hdfs.DFSClient.callAppend(DFSClient.java:1480)
        at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1520)
        at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1508)
        at org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:310)
        at org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:306)
        at org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
        at org.apache.hadoop.hdfs.DistributedFileSystem.append(DistributedFileSystem.java:306)
        at org.apache.hadoop.fs.FileSystem.append(FileSystem.java:1160)
        at org.lh.blog.message.hadoop.HdfsClient$2.run(HdfsClient.java:130)
        at org.lh.blog.message.hadoop.HdfsClient$2.run(HdfsClient.java:1)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:356)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1471)
        at org.lh.blog.message.hadoop.HdfsClient.appendTo(HdfsClient.java:121)
        at org.lh.blog.message.hadoop.HdfsClient.appendTo(HdfsClient.java:110)
        at org.lh.blog.message.test.HdfsClientTests.testCreateFileBeforeAppend(HdfsClientTests.java:26)
        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.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
        at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
        at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
        at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
        at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
        at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
        at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

也就是说，它在创建不存在的文件后只进行了一次追加操作，其他4次追加操作均失败，出现上述错误。我在 append 之前创建了文件，但它显示 AlreadyBeingCreatedException，我有些困惑。

我也有一些尝试。我发现用java API创建的hdfs文件，都不能做append操作。但是由 hdfs 命令(等，“hdfs dfs -put”)创建的 hdfs 文件可以进行追加操作。

你能帮帮我，给我一些建议吗？

感谢和问候。

Answer 1

为了解决这个问题，

1. 读取文件内容并将其存储到变量中。
2. 添加您希望 append 到此变量的新内容。
3. 重新创建文件并将您的内容写回它。

这个过程对我来说效果很好并解决了问题。

APPEND 操作代价高昂，如果您试图并行尝试它，那么这个问题就会出现。因此重新创建文件并将内容重新写入其中而不是 append 。