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courses:mapreduce-tutorial:step-26 [2012/01/28 15:29]
straka |
courses:mapreduce-tutorial:step-26 [2012/01/28 17:49]
straka |
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| The job properties can be set: | The job properties can be set: |
| * on the command line -- the [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/util/ToolRunner.html|ToolRunner]] parses options in format ''-Dname=value'' | * on the command line -- the [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/util/ToolRunner.html|ToolRunner]] parses options in format ''-Dname=value''. See the [[.:step-24#running-the-job|syntax of the hadoop script]]. |
| * using the [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Job.html|Job]] object. | * using the [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Job.html|Job]]''.getConfiguration()'' a [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/conf/Configuration.html|Configuration]] object is retrieved. It provides following methods: |
| See the [[.:step-9#a-brief-list-of-hadoop-options|brief list of Hadoop properties]]. | * ''String get(String name)'' -- get the value of the ''name'' property, ''null'' if it does not exist. |
| | * ''String get(String name, String defaultValue)'' -- get the value of the ''name'' property |
| | * ''getBoolean'', ''getClass'', ''getFile'', ''getFloat'', ''getInt'', ''getLong'', ''getStrings'' -- return a typed value of the ''name'' property (i.e., number, file name, class name, ...). |
| | * ''set(String name, String value)'' -- set the value of the ''name'' property to ''value''. |
| | * ''setBoolean'', ''setClass'', ''setFile'', ''setFloat'', ''setInt'', ''setLong'', ''setStrings'' -- set the typed value of the ''name'' property (i.e., number, file name, class name, ...). |
| | * in a mapper or a reducer, the ''context'' object also provides the ''getConfiguration()'' method, so the job properties can be accessed in the mappers and reducers too. |
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| There is one | Apart from already mentioned [[.:step-9#a-brief-list-of-hadoop-options|brief list of Hadoop properties]], there is one important Java-specific property: |
| | * **''mapred.child.java.opts''** with default value **''-Xmx200m''**. This property sets the Java options used for every task attempt (mapper, reducer, combiner, partitioner). The default value ''-Xmx200m'' specifies the maximum size of memory allocation pool. If your mappers and reducers need 1GB memory, use ''-Xmx1024m''. Other Java options can be found in ''man java''. |
