运行Pig时出现错误：
Pig Stack Trace
---------------
ERROR 1066: Unable to open iterator for alias visit. Backend error : java.net.ConnectException: Call From master/192.168.1.202 to 0.0.0.0:10020 failed on connection exception: java.net.ConnectException: 拒绝连接; For more details see: http://wiki.apache.org/hadoop/ConnectionRefused org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1066: Unable to open iterator for alias visit. Backend error : java.net.ConnectException: Call From master/192.168.1.202 to 0.0.0.0:10020 failed on connection exception: java.net.ConnectException: 拒绝连接; For more details see: http://wiki.apache.org/hadoop/ConnectionRefused
at org.apache.pig.PigServer.openIterator(PigServer.java:882)
at org.apache.pig.tools.grunt.GruntParser.processDump(GruntParser.java:774)
at org.apache.pig.tools.pigscript.parser.PigScriptParser.parse(PigScriptParser.java:372)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:198)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:173)
at org.apache.pig.tools.grunt.Grunt.run(Grunt.java:69)
at org.apache.pig.Main.run(Main.java:547)
at org.apache.pig.Main.main(Main.java:158)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.hadoop.util.RunJar.run(RunJar.java:221)
at org.apache.hadoop.util.RunJar.main(RunJar.java:136)
Caused by: java.io.IOException: java.net.ConnectException: Call From master/192.168.1.202 to 0.0.0.0:10020 failed on connection exception: java.net.ConnectException: 拒绝连接; For more details see: http://wiki.apache.org/hadoop/ConnectionRefused
at org.apache.hadoop.mapred.ClientServiceDelegate.invoke(ClientServiceDelegate.java:338)
at org.apache.hadoop.mapred.ClientServiceDelegate.getJobStatus(ClientServiceDelegate.java:423)
at org.apache.hadoop.mapred.YARNRunner.getJobStatus(YARNRunner.java:569)
at org.apache.hadoop.mapreduce.Cluster.getJob(Cluster.java:206)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:604)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:602)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698)
at org.apache.hadoop.mapred.JobClient.getJobUsingCluster(JobClient.java:602)
at org.apache.hadoop.mapred.JobClient.getTaskReports(JobClient.java:673)
at org.apache.hadoop.mapred.JobClient.getMapTaskReports(JobClient.java:667)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.Launcher.getStats(Launcher.java:150)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher.launchPig(MapReduceLauncher.java:428)
at org.apache.pig.PigServer.launchPlan(PigServer.java:1334)
at org.apache.pig.PigServer.executeCompiledLogicalPlan(PigServer.java:1319)
at org.apache.pig.PigServer.storeEx(PigServer.java:990)
at org.apache.pig.PigServer.store(PigServer.java:954)
at org.apache.pig.PigServer.openIterator(PigServer.java:867)
... 13 more
Caused by: java.net.ConnectException: Call From master/192.168.1.202 to 0.0.0.0:10020 failed on connection exception: java.net.ConnectException: 拒绝连接; For more details see: http://wiki.apache.org/hadoop/ConnectionRefused
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.apache.hadoop.net.NetUtils.wrapWithMessage(NetUtils.java:791)
at org.apache.hadoop.net.NetUtils.wrapException(NetUtils.java:731)
at org.apache.hadoop.ipc.Client.call(Client.java:1475)
at org.apache.hadoop.ipc.Client.call(Client.java:1408)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:230)
at com.sun.proxy.$Proxy14.getJobReport(Unknown Source)
at org.apache.hadoop.mapreduce.v2.api.impl.pb.client.MRClientProtocolPBClientImpl.getJobReport(MRClientProtocolPBClientImpl.java:133)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.hadoop.mapred.ClientServiceDelegate.invoke(ClientServiceDelegate.java:324)
... 31 more
Caused by: java.net.ConnectException: 拒绝连接
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:530)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:494)
at org.apache.hadoop.ipc.Client$Connection.setupConnection(Client.java:614)
at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:713)
at org.apache.hadoop.ipc.Client$Connection.access$2900(Client.java:375)
at org.apache.hadoop.ipc.Client.getConnection(Client.java:1524)
at org.apache.hadoop.ipc.Client.call(Client.java:1447)
... 40 more
这是因为没有启动jobhistoryserver，在mapred-site.xml中增加设置：
<property>
<name>mapreduce.jobhistory.address</name>
<value>master:10020</value>
</property>
然后再启动jobhistoryserver：
mr-jobhistory-daemon.sh start historyserver
以上命令需要在${HADOOP_HOME}/sbin/下执行。