1 Answers

Which MapReduce daemon instantiates user code, and executes map and reduce tasks on a cluster running MapReduce v1 (MRv1)?

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Which MapReduce daemon instantiates user code, and executes map and reduce tasks on a
cluster running MapReduce v1 (MRv1)?

A.
NameNode

B.
DataNode

C.
JobTracker

D.
TaskTracker

E.
ResourceManager

F.
ApplicationMaster

G.
NodeManager

1 Answers



  1. isamin on Jul 24, 2013 Reply

    Answers: D
    TaskTracker

    Explanation:
    A TaskTracker is a slave node daemon in the cluster that accepts tasks (Map,
    Reduce and Shuffle operations) from a JobTracker. There is only One Task Tracker process run
    on any hadoop slave node. Task Tracker runs on its own JVM process. Every TaskTracker is
    configured with a set ofslots, these indicate the number of tasks that it can accept. The
    TaskTracker starts a separate JVM processes to do the actual work (called as Task Instance) this
    is to ensure that process failure does not take down the task tracker. The TaskTracker monitors
    these task instances, capturing the output and exit codes. When the Task instances finish,
    successfully or not, the task tracker notifies the JobTracker. The TaskTrackers also send out
    heartbeat messages to the JobTracker, usually every few minutes, to reassure the JobTracker
    thatit is still alive. Thesemessage also inform the JobTracker of the number of available slots, so
    the JobTracker can stay up to date with where in the cluster work can be delegated.
    Note: How many Daemon processes run on a Hadoop system?
    Hadoop is comprised of five separate daemons. Each of these daemon run in its own JVM.
    Following 3 Daemons run on Masternodes NameNode – This daemon stores and maintains the
    metadata for HDFS.

    Secondary NameNode – Performs housekeeping functions for the NameNode.
    JobTracker – Manages MapReduce jobs, distributes individual tasks to machines running the Task
    Tracker.
    Following 2 Daemons run on each Slave nodes
    DataNode – Stores actual HDFS data blocks.
    TaskTracker – Responsible for instantiating and monitoring individual Map and Reduce tasks.
    Reference:
    24 Interview Questions & Answers for Hadoop MapReduce developers, What is a
    Task Tracker in Hadoop? How many instances of TaskTracker run on a Hadoop Cluster

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