Return-Path:
Users/admins can also specify the maximum virtual memory + of the launched child-task using mapred.child.ulimit.
When the job starts, the localized job directory ${mapred.local.dir}/taskTracker/jobcache/$jobid/ has the following directories:
@@ -1585,7 +1590,7 @@ loaded via System.loadLibrary or System.load. - +
@@ -1646,7 +1651,7 @@
Normally the user creates the application, describes various facets
of the job via JobConf, and then uses the
JobClient to submit the job and monitor its progress.
Users may need to chain map-reduce jobs to accomplish complex tasks which cannot be done via a single map-reduce job. This is fairly @@ -1682,7 +1687,7 @@ - +
@@ -1744,7 +1749,7 @@ FileSplit is the default InputSplit. It sets map.input.file to the path of the input file for the logical split.
- +
@@ -1781,7 +1786,7 @@
TextOutputFormat is the default
OutputFormat.
In some applications, component tasks need to create and/or write to side-files, which differ from the actual job-output files.
@@ -1820,7 +1825,7 @@The entire discussion holds true for maps of jobs with reducer=NONE (i.e. 0 reduces) since output of the map, in that case, goes directly to HDFS.
- +@@ -1828,9 +1833,9 @@ pairs to an output file.
RecordWriter implementations write the job outputs to the FileSystem.
- +Counters represent global counters, defined either by @@ -1844,7 +1849,7 @@ Reporter.incrCounter(Enum, long) in the map and/or reduce methods. These counters are then globally aggregated by the framework.
- +@@ -1877,7 +1882,7 @@ DistributedCache.createSymlink(Configuration) api. Files have execution permissions set.
- +The Tool interface supports the handling of generic Hadoop command-line options. @@ -1917,7 +1922,7 @@
- +
@@ -1941,7 +1946,7 @@
IsolationRunner will run the failed task in a single
jvm, which can be in the debugger, over precisely the same input.
Map/Reduce framework provides a facility to run user-provided scripts for debugging. When map/reduce task fails, user can run @@ -1952,7 +1957,7 @@
In the following sections we discuss how to submit debug script along with the job. For submitting debug script, first it has to distributed. Then the script has to supplied in Configuration.
- +To distribute the debug script file, first copy the file to the dfs. @@ -1975,7 +1980,7 @@ DistributedCache.createSymLink(Configuration) api.
- +A quick way to submit debug script is to set values for the properties "mapred.map.task.debug.script" and @@ -1999,17 +2004,17 @@ $script $stdout $stderr $syslog $jobconf $program
- +For pipes, a default script is run to process core dumps under gdb, prints stack trace and gives info about running threads.
- +JobControl is a utility which encapsulates a set of Map-Reduce jobs and their dependencies.
- +Hadoop Map-Reduce provides facilities for the application-writer to specify compression for both intermediate map-outputs and the @@ -2023,7 +2028,7 @@ codecs for reasons of both performance (zlib) and non-availability of Java libraries (lzo). More details on their usage and availability are available here.
- +Applications can control compression of intermediate map-outputs via the @@ -2044,7 +2049,7 @@ JobConf.setMapOutputCompressionType(SequenceFile.CompressionType) api.
- +Applications can control compression of job-outputs via the @@ -2064,7 +2069,7 @@ - +
Here is a more complete WordCount which uses many of the @@ -2074,7 +2079,7 @@ pseudo-distributed or fully-distributed Hadoop installation.
- +Sample text-files as input:
@@ -3452,7 +3457,7 @@
The second version of WordCount improves upon the previous one by using some features offered by the Map-Reduce framework: