map-default各种配置说明等

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<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>

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<!-- there.  If mapred-site.xml does not already exist, create it.      -->

<configuration>

<property>
  <name>hadoop.job.history.location</name>
  <value></value>
  <description> If job tracker is static the history files are stored 
  in this single well known place. If No value is set here, by default,
  it is in the local file system at ${hadoop.log.dir}/history.
  </description>
</property>

<property>
  <name>hadoop.job.history.user.location</name>
  <value></value>
  <description> User can specify a location to store the history files of 
  a particular job. If nothing is specified, the logs are stored in 
  output directory. The files are stored in "_logs/history/" in the directory.
  User can stop logging by giving the value "none". 
  </description>
</property>

<!-- i/o properties -->

<property>
  <name>io.sort.factor</name>
  <value>10</value>
  <description>The number of streams to merge at once while sorting
  files.  This determines the number of open file handles.</description>
</property>

<property>
  <name>io.sort.mb</name>
  <value>100</value>
  <description>The total amount of buffer memory to use while sorting 
  files, in megabytes.  By default, gives each merge stream 1MB, which
  should minimize seeks.</description>
</property>

<property>
  <name>io.sort.record.percent</name>
  <value>0.05</value>
  <description>The percentage of io.sort.mb dedicated to tracking record
  boundaries. Let this value be r, io.sort.mb be x. The maximum number
  of records collected before the collection thread must block is equal
  to (r * x) / 4</description>
</property>

<property>
  <name>io.sort.spill.percent</name>
  <value>0.80</value>
  <description>The soft limit in either the buffer or record collection
  buffers. Once reached, a thread will begin to spill the contents to disk
  in the background. Note that this does not imply any chunking of data to
  the spill. A value less than 0.5 is not recommended.</description>
</property>

<property>
  <name>io.map.index.skip</name>
  <value>0</value>
  <description>Number of index entries to skip between each entry.
  Zero by default. Setting this to values larger than zero can
  facilitate opening large map files using less memory.</description>
</property>

<property>
  <name>mapred.job.tracker</name>
  <value>local</value>
  <description>The host and port that the MapReduce job tracker runs
  at.  If "local", then jobs are run in-process as a single map
  and reduce task.
  </description>
</property>

<property>
  <name>mapred.job.tracker.http.address</name>
  <value>0.0.0.0:50030</value>
  <description>
    The job tracker http server address and port the server will listen on.
    If the port is 0 then the server will start on a free port.
  </description>
</property>

<property>
  <name>mapred.job.tracker.handler.count</name>
  <value>10</value>
  <description>
    The number of server threads for the JobTracker. This should be roughly
    4% of the number of tasktracker nodes.
  </description>
</property>

<property>
  <name>mapred.task.tracker.report.address</name>
  <value>127.0.0.1:0</value>
  <description>The interface and port that task tracker server listens on. 
  Since it is only connected to by the tasks, it uses the local interface.
  EXPERT ONLY. Should only be changed if your host does not have the loopback 
  interface.</description>
</property>

<property>
  <name>mapred.local.dir</name>
  <value>${hadoop.tmp.dir}/mapred/local</value>
  <description>The local directory where MapReduce stores intermediate
  data files.  May be a comma-separated list of
  directories on different devices in order to spread disk i/o.
  Directories that do not exist are ignored.
  </description>
</property>

<property>
  <name>mapred.system.dir</name>
  <value>${hadoop.tmp.dir}/mapred/system</value>
  <description>The shared directory where MapReduce stores control files.
  </description>
</property>

<property>
  <name>mapred.temp.dir</name>
  <value>${hadoop.tmp.dir}/mapred/temp</value>
  <description>A shared directory for temporary files.
  </description>
</property>

<property>
  <name>mapred.local.dir.minspacestart</name>
  <value>0</value>
  <description>If the space in mapred.local.dir drops under this, 
  do not ask for more tasks.
  Value in bytes.
  </description>
</property>

<property>
  <name>mapred.local.dir.minspacekill</name>
  <value>0</value>
  <description>If the space in mapred.local.dir drops under this, 
    do not ask more tasks until all the current ones have finished and 
    cleaned up. Also, to save the rest of the tasks we have running, 
    kill one of them, to clean up some space. Start with the reduce tasks,
    then go with the ones that have finished the least.
    Value in bytes.
  </description>
</property>

<property>
  <name>mapred.tasktracker.expiry.interval</name>
  <value>600000</value>
  <description>Expert: The time-interval, in miliseconds, after which
  a tasktracker is declared 'lost' if it doesn't send heartbeats.
  </description>
</property>

<property>
  <name>mapred.tasktracker.instrumentation</name>
  <value>org.apache.hadoop.mapred.TaskTrackerMetricsInst</value>
  <description>Expert: The instrumentation class to associate with each TaskTracker.
  </description>
</property>

<property>
  <name>mapred.tasktracker.memory_calculator_plugin</name>
  <value></value>
  <description>
   Name of the class whose instance will be used to query memory information
   on the tasktracker.
   
   The class must be an instance of 
   org.apache.hadoop.util.MemoryCalculatorPlugin. If the value is null, the
   tasktracker attempts to use a class appropriate to the platform. 
   Currently, the only platform supported is Linux.
  </description>
</property>

<property>
  <name>mapred.tasktracker.taskmemorymanager.monitoring-interval</name>
  <value>5000</value>
  <description>The interval, in milliseconds, for which the tasktracker waits
   between two cycles of monitoring its tasks' memory usage. Used only if
   tasks' memory management is enabled via mapred.tasktracker.tasks.maxmemory.
   </description>
</property>

<property>
  <name>mapred.tasktracker.procfsbasedprocesstree.sleeptime-before-sigkill</name>
  <value>5000</value>
  <description>The time, in milliseconds, the tasktracker waits for sending a
  SIGKILL to a process that has overrun memory limits, after it has been sent
  a SIGTERM. Used only if tasks' memory management is enabled via
  mapred.tasktracker.tasks.maxmemory.</description>
</property>

<property>
  <name>mapred.map.tasks</name>
  <value>2</value>
  <description>The default number of map tasks per job.
  Ignored when mapred.job.tracker is "local".  
  </description>
</property>

<property>
  <name>mapred.reduce.tasks</name>
  <value>1</value>
  <description>The default number of reduce tasks per job. Typically set to 99%
  of the cluster's reduce capacity, so that if a node fails the reduces can 
  still be executed in a single wave.
  Ignored when mapred.job.tracker is "local".
  </description>
</property>

<property>
  <name>mapred.jobtracker.restart.recover</name>
  <value>false</value>
  <description>"true" to enable (job) recovery upon restart,
               "false" to start afresh
  </description>
</property>

<property>
  <name>mapred.jobtracker.job.history.block.size</name>
  <value>3145728</value>
  <description>The block size of the job history file. Since the job recovery
               uses job history, its important to dump job history to disk as 
               soon as possible. Note that this is an expert level parameter.
               The default value is set to 3 MB.
  </description>
</property>

<property>
  <name>mapred.jobtracker.taskScheduler</name>
  <value>org.apache.hadoop.mapred.JobQueueTaskScheduler</value>
  <description>The class responsible for scheduling the tasks.</description>
</property>

<property>
  <name>mapred.jobtracker.taskScheduler.maxRunningTasksPerJob</name>
  <value></value>
  <description>The maximum number of running tasks for a job before
  it gets preempted. No limits if undefined.
  </description>
</property>

<property>
  <name>mapred.map.max.attempts</name>
  <value>4</value>
  <description>Expert: The maximum number of attempts per map task.
  In other words, framework will try to execute a map task these many number
  of times before giving up on it.
  </description>
</property>

<property>
  <name>mapred.reduce.max.attempts</name>
  <value>4</value>
  <description>Expert: The maximum number of attempts per reduce task.
  In other words, framework will try to execute a reduce task these many number
  of times before giving up on it.
  </description>
</property>

<property>
  <name>mapred.reduce.parallel.copies</name>
  <value>5</value>
  <description>The default number of parallel transfers run by reduce
  during the copy(shuffle) phase.
  </description>
</property>

<property>
  <name>mapred.reduce.copy.backoff</name>
  <value>300</value>
  <description>The maximum amount of time (in seconds) a reducer spends on 
  fetching one map output before declaring it as failed.
  </description>
</property>

<property>
  <name>mapred.task.timeout</name>
  <value>600000</value>
  <description>The number of milliseconds before a task will be
  terminated if it neither reads an input, writes an output, nor
  updates its status string.
  </description>
</property>

<property>
  <name>mapred.tasktracker.map.tasks.maximum</name>
  <value>2</value>
  <description>The maximum number of map tasks that will be run
  simultaneously by a task tracker.
  </description>
</property>

<property>
  <name>mapred.tasktracker.reduce.tasks.maximum</name>
  <value>2</value>
  <description>The maximum number of reduce tasks that will be run
  simultaneously by a task tracker.
  </description>
</property>

<property>
  <name>mapred.jobtracker.completeuserjobs.maximum</name>
  <value>100</value>
  <description>The maximum number of complete jobs per user to keep around 
  before delegating them to the job history.</description>
</property>

<property>
  <name>mapred.jobtracker.instrumentation</name>
  <value>org.apache.hadoop.mapred.JobTrackerMetricsInst</value>
  <description>Expert: The instrumentation class to associate with each JobTracker.
  </description>
</property>

<property>
  <name>mapred.child.java.opts</name>
  <value>-Xmx200m</value>
  <description>Java opts for the task tracker child processes.  
  The following symbol, if present, will be interpolated: @taskid@ is replaced 
  by current TaskID. Any other occurrences of '@' will go unchanged.
  For example, to enable verbose gc logging to a file named for the taskid in
  /tmp and to set the heap maximum to be a gigabyte, pass a 'value' of:
        -Xmx1024m -verbose:gc -Xloggc:/tmp/@taskid@.gc
  
  The configuration variable mapred.child.ulimit can be used to control the
  maximum virtual memory of the child processes. 
  </description>
</property>

<property>
  <name>mapred.child.ulimit</name>
  <value></value>
  <description>The maximum virtual memory, in KB, of a process launched by the 
  Map-Reduce framework. This can be used to control both the Mapper/Reducer 
  tasks and applications using Hadoop Pipes, Hadoop Streaming etc. 
  By default it is left unspecified to let cluster admins control it via 
  limits.conf and other such relevant mechanisms.
  
  Note: mapred.child.ulimit must be greater than or equal to the -Xmx passed to
  JavaVM, else the VM might not start. 
  </description>
</property>

<property>
  <name>mapred.child.tmp</name>
  <value>./tmp</value>
  <description> To set the value of tmp directory for map and reduce tasks.
  If the value is an absolute path, it is directly assigned. Otherwise, it is
  prepended with task's working directory. The java tasks are executed with
  option -Djava.io.tmpdir='the absolute path of the tmp dir'. Pipes and
  streaming are set with environment variable,
   TMPDIR='the absolute path of the tmp dir'
  </description>
</property>

<property>
  <name>mapred.inmem.merge.threshold</name>
  <value>1000</value>
  <description>The threshold, in terms of the number of files 
  for the in-memory merge process. When we accumulate threshold number of files
  we initiate the in-memory merge and spill to disk. A value of 0 or less than
  0 indicates we want to DON'T have any threshold and instead depend only on
  the ramfs's memory consumption to trigger the merge.
  </description>
</property>

<property>
  <name>mapred.job.shuffle.merge.percent</name>
  <value>0.66</value>
  <description>The usage threshold at which an in-memory merge will be
  initiated, expressed as a percentage of the total memory allocated to
  storing in-memory map outputs, as defined by
  mapred.job.shuffle.input.buffer.percent.
  </description>
</property>

<property>
  <name>mapred.job.shuffle.input.buffer.percent</name>
  <value>0.70</value>
  <description>The percentage of memory to be allocated from the maximum heap
  size to storing map outputs during the shuffle.
  </description>
</property>

<property>
  <name>mapred.job.reduce.input.buffer.percent</name>
  <value>0.0</value>
  <description>The percentage of memory- relative to the maximum heap size- to
  retain map outputs during the reduce. When the shuffle is concluded, any
  remaining map outputs in memory must consume less than this threshold before
  the reduce can begin.
  </description>
</property>

<property>
  <name>mapred.map.tasks.speculative.execution</name>
  <value>true</value>
  <description>If true, then multiple instances of some map tasks 
               may be executed in parallel.</description>
</property>

<property>
  <name>mapred.reduce.tasks.speculative.execution</name>
  <value>true</value>
  <description>If true, then multiple instances of some reduce tasks 
               may be executed in parallel.</description>
</property>

<property>
  <name>mapred.job.reuse.jvm.num.tasks</name>
  <value>1</value>
  <description>How many tasks to run per jvm. If set to -1, there is
  no limit. 
  </description>
</property>

<property>
  <name>mapred.min.split.size</name>
  <value>0</value>
  <description>The minimum size chunk that map input should be split
  into.  Note that some file formats may have minimum split sizes that
  take priority over this setting.</description>
</property>

<property>
  <name>mapred.jobtracker.maxtasks.per.job</name>
  <value>-1</value>
  <description>The maximum number of tasks for a single job.
  A value of -1 indicates that there is no maximum.  </description>
</property>

<property>
  <name>mapred.submit.replication</name>
  <value>10</value>
  <description>The replication level for submitted job files.  This
  should be around the square root of the number of nodes.
  </description>
</property>


<property>
  <name>mapred.tasktracker.dns.interface</name>
  <value>default</value>
  <description>The name of the Network Interface from which a task
  tracker should report its IP address.
  </description>
 </property>
 
<property>
  <name>mapred.tasktracker.dns.nameserver</name>
  <value>default</value>
  <description>The host name or IP address of the name server (DNS)
  which a TaskTracker should use to determine the host name used by
  the JobTracker for communication and display purposes.
  </description>
 </property>
 
<property>
  <name>tasktracker.http.threads</name>
  <value>40</value>
  <description>The number of worker threads that for the http server. This is
               used for map output fetching
  </description>
</property>

<property>
  <name>mapred.task.tracker.http.address</name>
  <value>0.0.0.0:50060</value>
  <description>
    The task tracker http server address and port.
    If the port is 0 then the server will start on a free port.
  </description>
</property>

<property>
  <name>keep.failed.task.files</name>
  <value>false</value>
  <description>Should the files for failed tasks be kept. This should only be 
               used on jobs that are failing, because the storage is never
               reclaimed. It also prevents the map outputs from being erased
               from the reduce directory as they are consumed.</description>
</property>


<!-- 
  <property>
  <name>keep.task.files.pattern</name>
  <value>.*_m_123456_0</value>
  <description>Keep all files from tasks whose task names match the given
               regular expression. Defaults to none.</description>
  </property>
-->

<property>
  <name>mapred.output.compress</name>
  <value>false</value>
  <description>Should the job outputs be compressed?
  </description>
</property>

<property>
  <name>mapred.output.compression.type</name>
  <value>RECORD</value>
  <description>If the job outputs are to compressed as SequenceFiles, how should
               they be compressed? Should be one of NONE, RECORD or BLOCK.
  </description>
</property>

<property>
  <name>mapred.output.compression.codec</name>
  <value>org.apache.hadoop.io.compress.DefaultCodec</value>
  <description>If the job outputs are compressed, how should they be compressed?
  </description>
</property>

<property>
  <name>mapred.compress.map.output</name>
  <value>false</value>
  <description>Should the outputs of the maps be compressed before being
               sent across the network. Uses SequenceFile compression.
  </description>
</property>

<property>
  <name>mapred.map.output.compression.codec</name>
  <value>org.apache.hadoop.io.compress.DefaultCodec</value>
  <description>If the map outputs are compressed, how should they be 
               compressed?
  </description>
</property>

<property>
  <name>map.sort.class</name>
  <value>org.apache.hadoop.util.QuickSort</value>
  <description>The default sort class for sorting keys.
  </description>
</property>

<property>
  <name>mapred.userlog.limit.kb</name>
  <value>0</value>
  <description>The maximum size of user-logs of each task in KB. 0 disables the cap.
  </description>
</property>

<property>
  <name>mapred.userlog.retain.hours</name>
  <value>24</value>
  <description>The maximum time, in hours, for which the user-logs are to be 
          retained.
  </description>
</property>

<property>
  <name>mapred.hosts</name>
  <value></value>
  <description>Names a file that contains the list of nodes that may
  connect to the jobtracker.  If the value is empty, all hosts are
  permitted.</description>
</property>

<property>
  <name>mapred.hosts.exclude</name>
  <value></value>
  <description>Names a file that contains the list of hosts that
  should be excluded by the jobtracker.  If the value is empty, no
  hosts are excluded.</description>
</property>

<property>
  <name>mapred.max.tracker.blacklists</name>
  <value>4</value>
  <description>The number of blacklists for a taskTracker by various jobs
               after which the task tracker could be blacklisted across
               all jobs. The tracker will be given a tasks later
               (after a day). The tracker will become a healthy
               tracker after a restart.
  </description>
</property> 

<property>
  <name>mapred.max.tracker.failures</name>
  <value>4</value>
  <description>The number of task-failures on a tasktracker of a given job 
               after which new tasks of that job aren't assigned to it.
  </description>
</property>

<property>
  <name>jobclient.output.filter</name>
  <value>FAILED</value>
  <description>The filter for controlling the output of the task's userlogs sent
               to the console of the JobClient. 
               The permissible options are: NONE, KILLED, FAILED, SUCCEEDED and 
               ALL.
  </description>
</property>

  <property>
    <name>mapred.job.tracker.persist.jobstatus.active</name>
    <value>false</value>
    <description>Indicates if persistency of job status information is
      active or not.
    </description>
  </property>

  <property>
  <name>mapred.job.tracker.persist.jobstatus.hours</name>
  <value>0</value>
  <description>The number of hours job status information is persisted in DFS.
    The job status information will be available after it drops of the memory
    queue and between jobtracker restarts. With a zero value the job status
    information is not persisted at all in DFS.
  </description>
</property>

  <property>
    <name>mapred.job.tracker.persist.jobstatus.dir</name>
    <value>/jobtracker/jobsInfo</value>
    <description>The directory where the job status information is persisted
      in a file system to be available after it drops of the memory queue and
      between jobtracker restarts.
    </description>
  </property>

  <property>
    <name>mapred.task.profile</name>
    <value>false</value>
    <description>To set whether the system should collect profiler
     information for some of the tasks in this job? The information is stored
     in the user log directory. The value is "true" if task profiling
     is enabled.</description>
  </property>

  <property>
    <name>mapred.task.profile.maps</name>
    <value>0-2</value>
    <description> To set the ranges of map tasks to profile.
    mapred.task.profile has to be set to true for the value to be accounted.
    </description>
  </property>

  <property>
    <name>mapred.task.profile.reduces</name>
    <value>0-2</value>
    <description> To set the ranges of reduce tasks to profile.
    mapred.task.profile has to be set to true for the value to be accounted.
    </description>
  </property>

  <property>
    <name>mapred.line.input.format.linespermap</name>
    <value>1</value>
    <description> Number of lines per split in NLineInputFormat.
    </description>
  </property>
  
  <property>
    <name>mapred.skip.attempts.to.start.skipping</name>
    <value>2</value>
    <description> The number of Task attempts AFTER which skip mode 
    will be kicked off. When skip mode is kicked off, the 
    tasks reports the range of records which it will process 
    next, to the TaskTracker. So that on failures, TT knows which 
    ones are possibly the bad records. On further executions, 
    those are skipped.
    </description>
  </property>
  
  <property>
    <name>mapred.skip.map.auto.incr.proc.count</name>
    <value>true</value>
    <description> The flag which if set to true, 
    SkipBadRecords.COUNTER_MAP_PROCESSED_RECORDS is incremented 
    by MapRunner after invoking the map function. This value must be set to 
    false for applications which process the records asynchronously 
    or buffer the input records. For example streaming. 
    In such cases applications should increment this counter on their own.
    </description>
  </property>
  
  <property>
    <name>mapred.skip.reduce.auto.incr.proc.count</name>
    <value>true</value>
    <description> The flag which if set to true, 
    SkipBadRecords.COUNTER_REDUCE_PROCESSED_GROUPS is incremented 
    by framework after invoking the reduce function. This value must be set to 
    false for applications which process the records asynchronously 
    or buffer the input records. For example streaming. 
    In such cases applications should increment this counter on their own.
    </description>
  </property>
  
  <property>
    <name>mapred.skip.out.dir</name>
    <value></value>
    <description> If no value is specified here, the skipped records are 
    written to the output directory at _logs/skip.
    User can stop writing skipped records by giving the value "none". 
    </description>
  </property>

  <property>
    <name>mapred.skip.map.max.skip.records</name>
    <value>0</value>
    <description> The number of acceptable skip records surrounding the bad 
    record PER bad record in mapper. The number includes the bad record as well.
    To turn the feature of detection/skipping of bad records off, set the 
    value to 0.
    The framework tries to narrow down the skipped range by retrying  
    until this threshold is met OR all attempts get exhausted for this task. 
    Set the value to Long.MAX_VALUE to indicate that framework need not try to 
    narrow down. Whatever records(depends on application) get skipped are 
    acceptable.
    </description>
  </property>
  
  <property>
    <name>mapred.skip.reduce.max.skip.groups</name>
    <value>0</value>
    <description> The number of acceptable skip groups surrounding the bad 
    group PER bad group in reducer. The number includes the bad group as well.
    To turn the feature of detection/skipping of bad groups off, set the 
    value to 0.
    The framework tries to narrow down the skipped range by retrying  
    until this threshold is met OR all attempts get exhausted for this task. 
    Set the value to Long.MAX_VALUE to indicate that framework need not try to 
    narrow down. Whatever groups(depends on application) get skipped are 
    acceptable.
    </description>
  </property>
  
<!-- Job Notification Configuration -->

<!--
<property>
 <name>job.end.notification.url</name>
 <value>http://localhost:8080/jobstatus.php?jobId=$jobId&amp;jobStatus=$jobStatus</value>
 <description>Indicates url which will be called on completion of job to inform
              end status of job.
              User can give at most 2 variables with URI : $jobId and $jobStatus.
              If they are present in URI, then they will be replaced by their
              respective values.
</description>
</property>
-->

<property>
  <name>job.end.retry.attempts</name>
  <value>0</value>
  <description>Indicates how many times hadoop should attempt to contact the
               notification URL </description>
</property>

<property>
  <name>job.end.retry.interval</name>
   <value>30000</value>
   <description>Indicates time in milliseconds between notification URL retry
                calls</description>
</property>
  
<!-- Proxy Configuration -->
<property>
  <name>hadoop.rpc.socket.factory.class.JobSubmissionProtocol</name>
  <value></value>
  <description> SocketFactory to use to connect to a Map/Reduce master
    (JobTracker). If null or empty, then use hadoop.rpc.socket.class.default.
  </description>
</property>

<property>
  <name>mapred.task.cache.levels</name>
  <value>2</value>
  <description> This is the max level of the task cache. For example, if
    the level is 2, the tasks cached are at the host level and at the rack
    level.
  </description>
</property>

<property>
  <name>mapred.queue.names</name>
  <value>default</value>
  <description> Comma separated list of queues configured for this jobtracker.
    Jobs are added to queues and schedulers can configure different 
    scheduling properties for the various queues. To configure a property 
    for a queue, the name of the queue must match the name specified in this 
    value. Queue properties that are common to all schedulers are configured 
    here with the naming convention, mapred.queue.$QUEUE-NAME.$PROPERTY-NAME,
    for e.g. mapred.queue.default.submit-job-acl.
    The number of queues configured in this parameter could depend on the
    type of scheduler being used, as specified in 
    mapred.jobtracker.taskScheduler. For example, the JobQueueTaskScheduler
    supports only a single queue, which is the default configured here.
    Before adding more queues, ensure that the scheduler you've configured
    supports multiple queues.
  </description>
</property>

<property>
  <name>mapred.acls.enabled</name>
  <value>false</value>
  <description> Specifies whether ACLs are enabled, and should be checked
    for various operations.
  </description>
</property>

<property>
  <name>mapred.queue.default.acl-submit-job</name>
  <value>*</value>
  <description> Comma separated list of user and group names that are allowed
    to submit jobs to the 'default' queue. The user list and the group list
    are separated by a blank. For e.g. alice,bob group1,group2. 
    If set to the special value '*', it means all users are allowed to 
    submit jobs. 
  </description>
</property>

<property>
  <name>mapred.queue.default.acl-administer-jobs</name>
  <value>*</value>
  <description> Comma separated list of user and group names that are allowed
    to delete jobs or modify job's priority for jobs not owned by the current
    user in the 'default' queue. The user list and the group list
    are separated by a blank. For e.g. alice,bob group1,group2. 
    If set to the special value '*', it means all users are allowed to do 
    this operation.
  </description>
</property>

<property>
  <name>mapred.job.queue.name</name>
  <value>default</value>
  <description> Queue to which a job is submitted. This must match one of the
    queues defined in mapred.queue.names for the system. Also, the ACL setup
    for the queue must allow the current user to submit a job to the queue.
    Before specifying a queue, ensure that the system is configured with 
    the queue, and access is allowed for submitting jobs to the queue.
  </description>
</property>

<property>
  <name>mapred.tasktracker.indexcache.mb</name>
  <value>10</value>
  <description> The maximum memory that a task tracker allows for the 
    index cache that is used when serving map outputs to reducers.
  </description>
</property>

<property>
  <name>mapred.merge.recordsBeforeProgress</name>
  <value>10000</value>
  <description> The number of records to process during merge before
   sending a progress notification to the TaskTracker.
  </description>
</property>

<property>
  <name>mapred.reduce.slowstart.completed.maps</name>
  <value>0.05</value>
  <description>Fraction of the number of maps in the job which should be 
  complete before reduces are scheduled for the job. 
  </description>
</property>

</configuration>