hadoop.job.history.location 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. hadoop.job.history.user.location 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". io.sort.factor 10 The number of streams to merge at once while sorting files. This determines the number of open file handles. io.sort.mb 100 The total amount of buffer memory to use while sorting files, in megabytes. By default, gives each merge stream 1MB, which should minimize seeks. io.sort.record.percent 0.05 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 io.sort.spill.percent 0.80 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. io.map.index.skip 0 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. mapred.job.tracker local 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. mapred.job.tracker.http.address 0.0.0.0:50030 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. mapred.job.tracker.handler.count 10 The number of server threads for the JobTracker. This should be roughly 4% of the number of tasktracker nodes. mapred.task.tracker.report.address 127.0.0.1:0 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. mapred.local.dir ${hadoop.tmp.dir}/mapred/local 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. mapred.system.dir ${hadoop.tmp.dir}/mapred/system The shared directory where MapReduce stores control files. mapred.temp.dir ${hadoop.tmp.dir}/mapred/temp A shared directory for temporary files. mapred.local.dir.minspacestart 0 If the space in mapred.local.dir drops under this, do not ask for more tasks. Value in bytes. mapred.local.dir.minspacekill 0 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. mapred.tasktracker.expiry.interval 600000 Expert: The time-interval, in miliseconds, after which a tasktracker is declared 'lost' if it doesn't send heartbeats. mapred.tasktracker.instrumentation org.apache.hadoop.mapred.TaskTrackerMetricsInst Expert: The instrumentation class to associate with each TaskTracker. mapred.tasktracker.memory_calculator_plugin 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. mapred.tasktracker.taskmemorymanager.monitoring-interval 5000 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. mapred.tasktracker.procfsbasedprocesstree.sleeptime-before-sigkill 5000 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. mapred.map.tasks 2 The default number of map tasks per job. Ignored when mapred.job.tracker is "local". mapred.reduce.tasks 1 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". mapred.jobtracker.restart.recover false "true" to enable (job) recovery upon restart, "false" to start afresh mapred.jobtracker.job.history.block.size 3145728 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. mapred.jobtracker.taskScheduler org.apache.hadoop.mapred.JobQueueTaskScheduler The class responsible for scheduling the tasks. mapred.jobtracker.taskScheduler.maxRunningTasksPerJob The maximum number of running tasks for a job before it gets preempted. No limits if undefined. mapred.map.max.attempts 4 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. mapred.reduce.max.attempts 4 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. mapred.reduce.parallel.copies 5 The default number of parallel transfers run by reduce during the copy(shuffle) phase. mapred.reduce.copy.backoff 300 The maximum amount of time (in seconds) a reducer spends on fetching one map output before declaring it as failed. mapred.task.timeout 600000 The number of milliseconds before a task will be terminated if it neither reads an input, writes an output, nor updates its status string. mapred.tasktracker.map.tasks.maximum 2 The maximum number of map tasks that will be run simultaneously by a task tracker. mapred.tasktracker.reduce.tasks.maximum 2 The maximum number of reduce tasks that will be run simultaneously by a task tracker. mapred.jobtracker.completeuserjobs.maximum 100 The maximum number of complete jobs per user to keep around before delegating them to the job history. mapred.jobtracker.instrumentation org.apache.hadoop.mapred.JobTrackerMetricsInst Expert: The instrumentation class to associate with each JobTracker. mapred.child.java.opts -Xmx200m 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. mapred.child.ulimit 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. mapred.child.tmp ./tmp 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' mapred.inmem.merge.threshold 1000 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. mapred.job.shuffle.merge.percent 0.66 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. mapred.job.shuffle.input.buffer.percent 0.70 The percentage of memory to be allocated from the maximum heap size to storing map outputs during the shuffle. mapred.job.reduce.input.buffer.percent 0.0 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. mapred.map.tasks.speculative.execution true If true, then multiple instances of some map tasks may be executed in parallel. mapred.reduce.tasks.speculative.execution true If true, then multiple instances of some reduce tasks may be executed in parallel. mapred.job.reuse.jvm.num.tasks 1 How many tasks to run per jvm. If set to -1, there is no limit. mapred.min.split.size 0 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. mapred.jobtracker.maxtasks.per.job -1 The maximum number of tasks for a single job. A value of -1 indicates that there is no maximum. mapred.submit.replication 10 The replication level for submitted job files. This should be around the square root of the number of nodes. mapred.tasktracker.dns.interface default The name of the Network Interface from which a task tracker should report its IP address. mapred.tasktracker.dns.nameserver default 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. tasktracker.http.threads 40 The number of worker threads that for the http server. This is used for map output fetching mapred.task.tracker.http.address 0.0.0.0:50060 The task tracker http server address and port. If the port is 0 then the server will start on a free port. keep.failed.task.files false 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. mapred.output.compress false Should the job outputs be compressed? mapred.output.compression.type RECORD If the job outputs are to compressed as SequenceFiles, how should they be compressed? Should be one of NONE, RECORD or BLOCK. mapred.output.compression.codec org.apache.hadoop.io.compress.DefaultCodec If the job outputs are compressed, how should they be compressed? mapred.compress.map.output false Should the outputs of the maps be compressed before being sent across the network. Uses SequenceFile compression. mapred.map.output.compression.codec org.apache.hadoop.io.compress.DefaultCodec If the map outputs are compressed, how should they be compressed? map.sort.class org.apache.hadoop.util.QuickSort The default sort class for sorting keys. mapred.userlog.limit.kb 0 The maximum size of user-logs of each task in KB. 0 disables the cap. mapred.userlog.retain.hours 24 The maximum time, in hours, for which the user-logs are to be retained. mapred.hosts Names a file that contains the list of nodes that may connect to the jobtracker. If the value is empty, all hosts are permitted. mapred.hosts.exclude 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. mapred.max.tracker.blacklists 4 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. mapred.max.tracker.failures 4 The number of task-failures on a tasktracker of a given job after which new tasks of that job aren't assigned to it. jobclient.output.filter FAILED 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. mapred.job.tracker.persist.jobstatus.active false Indicates if persistency of job status information is active or not. mapred.job.tracker.persist.jobstatus.hours 0 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. mapred.job.tracker.persist.jobstatus.dir /jobtracker/jobsInfo 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. mapred.task.profile false 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. mapred.task.profile.maps 0-2 To set the ranges of map tasks to profile. mapred.task.profile has to be set to true for the value to be accounted. mapred.task.profile.reduces 0-2 To set the ranges of reduce tasks to profile. mapred.task.profile has to be set to true for the value to be accounted. mapred.line.input.format.linespermap 1 Number of lines per split in NLineInputFormat. mapred.skip.attempts.to.start.skipping 2 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. mapred.skip.map.auto.incr.proc.count true 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. mapred.skip.reduce.auto.incr.proc.count true 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. mapred.skip.out.dir 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". mapred.skip.map.max.skip.records 0 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. mapred.skip.reduce.max.skip.groups 0 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. job.end.retry.attempts 0 Indicates how many times hadoop should attempt to contact the notification URL job.end.retry.interval 30000 Indicates time in milliseconds between notification URL retry calls hadoop.rpc.socket.factory.class.JobSubmissionProtocol SocketFactory to use to connect to a Map/Reduce master (JobTracker). If null or empty, then use hadoop.rpc.socket.class.default. mapred.task.cache.levels 2 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. mapred.queue.names default 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. mapred.acls.enabled false Specifies whether ACLs are enabled, and should be checked for various operations. mapred.queue.default.acl-submit-job * 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. mapred.queue.default.acl-administer-jobs * 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. mapred.job.queue.name default 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. mapred.tasktracker.indexcache.mb 10 The maximum memory that a task tracker allows for the index cache that is used when serving map outputs to reducers. mapred.merge.recordsBeforeProgress 10000 The number of records to process during merge before sending a progress notification to the TaskTracker. mapred.reduce.slowstart.completed.maps 0.05 Fraction of the number of maps in the job which should be complete before reduces are scheduled for the job.