namevaluedescription
io.sort.factor10The number of streams to merge at once while sorting files. This determines the number of open file handles.
io.sort.mb100The total amount of buffer memory to use while sorting files, in megabytes. By default, gives each merge stream 1MB, which should minimize seeks.
io.file.buffer.size4096The size of buffer for use in sequence files. The size of this buffer should probably be a multiple of hardware page size (4096 on Intel x86), and it determines how much data is buffered during read and write operations.
io.bytes.per.checksum512The number of bytes per checksum. Must not be larger than io.file.buffer.size.
io.skip.checksum.errorsfalseIf true, when a checksum error is encountered while reading a sequence file, entries are skipped, instead of throwing an exception.
io.map.index.skip0Number 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.
fs.default.namelocalThe name of the default file system. Either the literal string "local" or a host:port for DFS.
dfs.datanode.port50010The port number that the dfs datanode server uses as a starting point to look for a free port to listen on.
dfs.name.dir/tmp/hadoop/dfs/nameDetermines where on the local filesystem the DFS name node should store the name table.
dfs.data.dir/tmp/hadoop/dfs/dataDetermines where on the local filesystem an DFS data node should store its blocks. If this is a comma- or space-delimited list of directories, then data will be stored in all named directories, typically on different devices.
dfs.replication3How many copies we try to have at all times. The actual number of replications is at max the number of datanodes in the cluster.
dfs.df.interval3000Disk usage statistics refresh interval in msec.
mapred.job.trackerlocalThe 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.info.port50030The port that the MapReduce job tracker info webserver runs at.
mapred.task.tracker.output.port50040The port number that the MapReduce task tracker output server uses as a starting point to look for a free port to listen on.
mapred.task.tracker.report.port50050The port number that the MapReduce task tracker report server uses as a starting point to look for a free port to listen on.
mapred.local.dir/tmp/hadoop/mapred/localThe local directory where MapReduce stores intermediate data files. May be a space- or comma- separated list of directories on different devices in order to spread disk i/o.
mapred.system.dir/tmp/hadoop/mapred/systemThe shared directory where MapReduce stores control files.
mapred.temp.dir/tmp/hadoop/mapred/tempA shared directory for temporary files.
mapred.map.tasks2The default number of map tasks per job. Typically set to a prime several times greater than number of available hosts. Ignored when mapred.job.tracker is "local".
mapred.reduce.tasks1The default number of reduce tasks per job. Typically set to a prime close to the number of available hosts. Ignored when mapred.job.tracker is "local".
mapred.task.timeout600000The 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.tasks.maximum2The maximum number of tasks that will be run simultaneously by a task tracker.
mapred.child.java.opts-Xmx200mJava opts for the task tracker child processes. Subsumes 'mapred.child.heap.size' (If a mapred.child.heap.size value is found in a configuration, its maximum heap size will be used and a warning emitted that heap.size has been deprecated). Also, the following symbols, if present, will be interpolated: @taskid@ is replaced by current TaskID; and @port@ will be replaced by mapred.task.tracker.report.port + 1 (A second child will fail with a port-in-use if mapred.tasktracker.tasks.maximum is greater than one). 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
mapred.combine.buffer.size100000The number of entries the combining collector caches before combining them and writing to disk.
mapred.speculative.executiontrueIf true, then multiple instances of some map tasks may be executed in parallel.
mapred.min.split.size0The 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.
ipc.client.timeout60000Defines the timeout for IPC calls in milliseconds.