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    Comma-separated list of datanode plug-ins to be activated.
    It is used by jobtracker to create task caches for node at various levels.this makes data locality scheduling possible. If I set mapred.task.cache.levels to 0 & use default network topology then MR job will stall forever.The reason is JobInProgress::find NewMapTask always return -1.Field “nonRunningMapCache” is empty & field ” nonLocalMaps” is empty.
    Haddop.tmp.dir is used as a temporary directory for both local file system & for HDFS.We will use the directory ‘/app/hadoop/tmp/’.We need to create the directory & change the ownership.
    The method map.sort.class determines the sorting algorithm used for sorting keys.the default is QuickSort implemented in org.apache.hadoop.util.QuickSort.
    The no:of nodes namenode checks if decommission is complete in each dfs.namenode. decommission.interval
    Table from which to fetch data mapreduce jdbc.input.field.names columns to fetch.jdbc.input.field.orderby column by which splitting will happen across various mapper .this propertly controls the parallelizatin of fetching data from db. is used by the datanode to set the permission of its data directories.
    The directory where mapreduce store control files.
    The no:of hours job status information is persisted in dfs the job status info will be available after it drops of memory queue b/w job tracker restarts.

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