感觉程序员的世界真是一个变幻无常且精彩绝伦的世界，每次跑程序都会发现不一样的问题。今天跑MapReduce程序来统计邮箱次数时遇到了一个问题，明明一样的代码，别人能跑，我却跑不了。我相信，基本做这行的都遇到过这种问题。好了，话不多说，来聊聊今天的错误吧。
根据日志查看到报的错误为：No lease on /目录: File does not exist. [Lease. Holder: DFSClient_NONMAPREDUCE_-2059237550_1, pendingcreates: 8]，详细信息如下面日志所示。
2018-04-02 15:05:04,669 DEBUG [org.apache.hadoop.ipc.Client] - IPC Client (2124974876) connection to ******* from Zimo sending #55
2018-04-02 15:05:04,670 DEBUG [org.apache.hadoop.ipc.Client] - IPC Client (2124974876) connection to ******* from Zimo got value #55
2018-04-02 15:05:04,671 WARN [org.apache.hadoop.hdfs.DFSClient] - DataStreamer Exception
org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.server.namenode.LeaseExpiredException): No lease on /email/out/_temporary/0/_temporary/attempt_local1331388695_0001_r_000000_0/163-r-00000: File does not exist. [Lease. Holder: DFSClient_NONMAPREDUCE_-979457887_1, pendingcreates: 8]
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.checkLease(FSNamesystem.java:2737)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.analyzeFileState(FSNamesystem.java:2543)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2454)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:555)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:387)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java:59582)
at org.apache.hadoop.ipc.ProtobufRpcEngine$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$Invoker.invoke(ProtobufRpcEngine.java:206)
at com.sun.proxy.$Proxy9.addBlock(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
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.$Proxy9.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:330)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:1226)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1078)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:514)
2018-04-02 15:05:04,671 ERROR [org.apache.hadoop.hdfs.DFSClient] - Failed to close file /email/out/_temporary/0/_temporary/attempt_local1331388695_0001_r_000000_0/163-r-00000
org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.server.namenode.LeaseExpiredException): No lease on /email/out/_temporary/0/_temporary/attempt_local1331388695_0001_r_000000_0/163-r-00000: File does not exist. [Lease. Holder: DFSClient_NONMAPREDUCE_-979457887_1, pendingcreates: 8]
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.checkLease(FSNamesystem.java:2737)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.analyzeFileState(FSNamesystem.java:2543)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2454)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:555)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:387)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java:59582)
at org.apache.hadoop.ipc.ProtobufRpcEngine$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$Invoker.invoke(ProtobufRpcEngine.java:206)
at com.sun.proxy.$Proxy9.addBlock(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
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.$Proxy9.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:330)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:1226)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1078)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:514)
2018-04-02 15:05:04,672 DEBUG [org.apache.hadoop.ipc.Client] - Stopping client
在前面跑MapReduce程序的时候没有出现过这个错误，就今天遇到了。遇到这个错误时需要在Reducer代码中加上cleanup方法以重新执行。
protected void cleanup(Context context) throws IOException,InterruptedException {
multipleOutputs.close();
}
cleanup()方法会被MapReduce框架仅且执行一次，在执行完毕Map任务后，进行相关变量或资源的释放工作。若是将释放资源工作放入方法map()中，也会导致Mapper任务在解析、处理每一行文本后释放资源，而且在下一行文本解析前还要重复初始化，导致反复重复，程序运行效率不高！
现在我们再重新运行一次程序就会发现问题已经解决了！
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