hadoop - 只能复制到 0 个节点而不是 minReplication (=1)。有 4 个数据节点正在运行，并且没有节点被排除在此操作中

Question

我不知道如何解决这个错误:

Vertex failed, vertexName=initialmap, vertexId=vertex_1449805139484_0001_1_00, diagnostics=[Task failed, taskId=task_1449805139484_0001_1_00_000003, diagnostics=[AttemptID:attempt_1449805139484_0001_1_00_000003_0 Info:Error: org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /user/hadoop/gridmix-kon/input/_temporary/1/_temporary/attempt_14498051394840_0001_m_000003_0/part-m-00003/segment-121 could only be replicated to 0 nodes instead of minReplication (=1). There are 4 datanode(s) running and no node(s) are excluded in this operation.
at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget(BlockManager.java:1441)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2702)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:584)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:440)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:585)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:928)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2014)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2010)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1561)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2008)
at org.apache.hadoop.ipc.Client.call(Client.java:1411)
at org.apache.hadoop.ipc.Client.call(Client.java:1364)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:206)
at com.sun.proxy.$Proxy17.addBlock(Unknown Source)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
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:190)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:103)
at com.sun.proxy.$Proxy17.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:361)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:1439)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1261)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:525)

知道是怎么回事吗？

Answer 1

这个错误发生在BlockManager::chooseTarget4NewBlock() (我指的是最新的代码)代码。导致这种情况的具体代码是:

final DatanodeStorageInfo[] targets = blockplacement.chooseTarget(src,
    numOfReplicas, client, excludedNodes, blocksize, 
    favoredDatanodeDescriptors, storagePolicy);

if (targets.length < minReplication) {
  throw new IOException("File " + src + " could only be replicated to "
      + targets.length + " nodes instead of minReplication (="
      + minReplication + ").  There are "
      + getDatanodeManager().getNetworkTopology().getNumOfLeaves()
      + " datanode(s) running and "
      + (excludedNodes == null? "no": excludedNodes.size())
      + " node(s) are excluded in this operation.");
}

这发生在 BlockManager 时尝试选择一个目标主机来存储新的数据 block ，但找不到单个主机 (targets.length < minReplication) . minReplication在dfs.namenode.replication.min中设置为1(配置参数:hdfs-site.xml)文件。

这可能是由于以下原因之一造成的:

• 数据节点实例没有运行
• 数据节点实例无法联系名称节点
• 数据节点已经用完空间，因此不能分配新的数据 block 给它们

但是，在您的情况下，错误消息还包含以下信息:

There are 4 datanode(s) running and no node(s) are excluded in this operation.

这意味着，有 4 个数据节点在运行，并且所有 4 个数据节点都被考虑放置数据，用于此操作。

因此，可能怀疑是数据节点上的磁盘空间。您可以使用以下命令检查数据节点上的磁盘空间:

hdfs dfsadmin -report

它为每个实时数据节点提供报告。例如就我而言，我得到了以下信息:

Live datanodes (1):

Name: 192.168.56.1:50010 (192.168.56.1)
Hostname: 192.168.56.1
Decommission Status : Normal
Configured Capacity: 648690003968 (604.14 GB)
DFS Used: 193849055737 (180.54 GB)
Non DFS Used: 186164975111 (173.38 GB)
DFS Remaining: 268675973120 (250.22 GB)
DFS Used%: 29.88%
DFS Remaining%: 41.42%
Configured Cache Capacity: 0 (0 B)
Cache Used: 0 (0 B)
Cache Remaining: 0 (0 B)
Cache Used%: 100.00%
Cache Remaining%: 0.00%
Xceivers: 1
Last contact: Sun Dec 13 17:17:34 IST 2015

检查“DFS-Remaining”和“DFS-Remaining%”。这应该让您了解数据节点上的剩余空间。

您也可以在这里引用 wiki:https://wiki.apache.org/hadoop/CouldOnlyBeReplicatedTo ，其中描述了此错误的原因以及缓解错误的方法。