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    1) what are the external daemons running on standalone mode ?

    In standalone mode, there are no external daemons. JVM daemons itself will work as external daemons.

    2) How to control job running on DN ?

    To start all Daemons

    To control job running on DataNode
    ./ start datanode
    ./ stop datanode

    3) How to define trash path ?

    Once the trash feature is enabled, when you remove files from HDFS , files or directories will not be wiped out immediately, instead, they will be moved to a trash directory.

    By default the Trash path is /user/<username>/.Trash

    We can set the trash deletion and emptier interval by specifing these properties in core-ste.xml : “fs.trash.interval” and “fs.trash.checkpoint.interval”

    Deletion interval:specifies how long (in minutes) a checkpoint will be expired before it is deleted.
    It is the value of fs.trash.interval. The NameNode runs a thread to periodically remove expired checkpoints from the file system.

    Emptier interval:specifies how long (in minutes) the NameNode waits before running a thread to manage checkpoints.
    The NameNode deletes checkpoints that are older than fs.trash.interval and creates a new checkpoint from /user/${username}/.Trash/Current.
    This frequency is determined by the value of fs.trash.checkpoint.interval, and it must not be greater than the deletion interval.
    This ensures that in an emptier window, there are one or more checkpoints in the trash

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Reply To: Module 2 : Clusters
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