如何设置Hadoop Map/Reduce任务的内存限制？
Parameter Type Meaningmapred.cluster.map.memory.mb set by admin, cluster-wide Cluster definition of memory per map slot. The maximum amount of memory, in MB, each map task on a tasktracker can consume.
mapred.cluster.reduce.memory.mb set by admin, cluster-wide Cluster definition of memory per reduce slot. The maximum amount of memory, in MB, each reduce task on a tasktracker can consume.
mapred.job.map.memory.mb set by user, per-job Job requirement for map tasks. The maximum amount of memory each map task of a job can consume, in MB.
mapred.job.reduce.memory.mb set by user, per-job job requirement for reduce tasks. The maximum amount of memory each reduce task of a job can consume, in MB.
mapred.cluster.max.map.memory.mb set by admin, cluster-wide Max limit on jobs. The maximum value that can be specified by a user via mapred.job.map.memory.mb, in MB. A job that asks for more than this number will be failed at submission itself.
mapred.cluster.max.reduce.memory.mb set by admin, cluster-wide Max limit on jobs. The maximum value that can be specified by a user via mapred.job.reduce.memory.mb, in MB. A job that asks for more than this number will be failed at submission itself.
不设置时默认都是-1，无限制
相关介绍请参考Hadoop-0.20.2 作业内存控制策略分析
设置时请注意其大小关系。比如你设置了mapred.cluster.map.memory.mb为1024 ，然后你提交任务时没有设置mapred.job.map.memory.mb(默认为-1，无限制)，此时便会报如下错误：
2012-06-13 16:18:10,951 ERROR exec.Task (SessionState.java:printError(380)) - Job Submission failed with exception 'org.apache.hadoop.ipc.RemoteException(java.io.IOException: job_201206131602_0003(-1 memForMapTasks -1 memForReduceTasks): Invalid job requirements. at org.apache.hadoop.mapred.JobTracker.checkMemoryRequirements(JobTracker.java:5160) at org.apache.hadoop.mapred.JobTracker.submitJob(JobTracker.java:3949) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:523) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1383) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1379) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1059) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1377) )' org.apache.hadoop.ipc.RemoteException: java.io.IOException: job_201206131602_0003(-1 memForMapTasks -1 memForReduceTasks): Invalid job requirements. at org.apache.hadoop.mapred.JobTracker.checkMemoryRequirements(JobTracker.java:5160) at org.apache.hadoop.mapred.JobTracker.submitJob(JobTracker.java:3949) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:523) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1383) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1379) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1059) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1377) at org.apache.hadoop.ipc.Client.call(Client.java:1030) at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:224) at org.apache.hadoop.mapred.$Proxy7.submitJob(Unknown Source) at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:862) at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:791) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1059) at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:791) at org.apache.hadoop.mapred.JobClient.submitJob(JobClient.java:765) at org.apache.hadoop.hive.ql.exec.ExecDriver.execute(ExecDriver.java:452) at org.apache.hadoop.hive.ql.exec.MapRedTask.execute(MapRedTask.java:136) at org.apache.hadoop.hive.ql.exec.Task.executeTask(Task.java:133) at org.apache.hadoop.hive.ql.exec.TaskRunner.runSequential(TaskRunner.java:57) at org.apache.hadoop.hive.ql.Driver.launchTask(Driver.java:1332) at org.apache.hadoop.hive.ql.Driver.execute(Driver.java:1123) at org.apache.hadoop.hive.ql.Driver.run(Driver.java:931) at org.apache.hadoop.hive.service.HiveServer$HiveServerHandler.execute(HiveServer.java:191) at org.apache.hadoop.hive.service.ThriftHive$Processor$execute.getResult(ThriftHive.java:629) at org.apache.hadoop.hive.service.ThriftHive$Processor$execute.getResult(ThriftHive.java:617) at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:32) at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:34) at org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:176)