What is MapReduce in Hadoop?


Hadoop provides the robust, distributed processing of enormous unstructured data volumes across commodity computer clusters, each with its own storage. MapReduce performs two critical functions: it filters and distributes work to different nodes within the cluster or map, a function known as the mapper, and it organizes and reduces the data from each node into a coherent answer to a query, known as the reducer.

How does MapReduce work?

The original MapReduce version had a number of component daemons, including:

JobTracker is the cluster’s master node, in charge of all jobs and resources.

TaskTrackers are agents that are installed on each computer in the cluster to map and reduce tasks, whereas JobHistory Server is a component that monitors completed jobs and is commonly used as a standalone function or in conjunction with JobTracker.

Previous Job Tracker and Task Tracker daemons were replaced by components of Yet Another Resource Negotiator (YARN), dubbed Resource Manager and Node Manager, with the release of MapReduce and Hadoop version 2.

ResourceManager is a master node that manages job submission and scheduling on the cluster. It also keeps track of jobs and assigns resources. NodeManager runs on slave nodes and collaborates with the Resource Manager to execute tasks and monitor resource utilization.

MapReduce runs in parallel over huge cluster sizes to spread input data and collate outcomes. Because cluster size has no effect on the final output of a processing operation, jobs can be distributed among practically any number of computers. As a result, MapReduce and Hadoop in general.

MapReduce is accessible in a variety of programming languages, including C, C++, Java, Ruby, Perl, and Python. MapReduce libraries allow programmers to build jobs without having to worry about communication or coordination between nodes. If a node fails to reply as expected, the master node reassigns that portion of the work to other nodes in the cluster that are available. This increases robustness and allows MapReduce to run on low-cost commodity servers.

Job Tracker

1. The JobTracker process is normally operated on a separate node and not on a Data Node.

2. In MRv1, JobTracker is a required Daemon for MapReduce execution. In MRv2, it is replaced by ResourceManager/ApplicationMaster.

3. JobTracker handles client requests for MapReduce execution.

4. To determine the location of the data, JobTracker communicates with the NameNode.

5. JobTracker selects the optimal TaskTracker nodes for job execution based on data locality (data closeness) and availability slots to perform a task on a specific node.

6. JobTracker monitors the various TaskTrackers and reports back to the customer on the overall state of the task.

7. In terms of MapReduce execution, the JobTracker process is crucial to the Hadoop cluster.
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Examples and Applications of MapReduce

MapReduce’s strength is in its ability to handle large data sets by distributing processing over many nodes and then combining or reducing the results of those nodes.

As a simple example, users might use a single server application to list and calculate the number of times each word appears in a novel, but this is time-consuming. Users, on the other hand, can divide the job among 26 individuals, such that each person takes a page, writes a word on a separate piece of paper, and then takes a new page when they’re completed.

This is MapReduce’s map component. And if someone departs, someone else takes his or her position. This shows the fault-tolerant nature of MapReduce.

When all of the pages have been processed, users organize their single-word pages into 26 boxes, one for each letter of the word. Each user takes a box and alphabetically organizes each word in the stack. The number of pages with the same term is an example of MapReduce’s reduce feature.

MapReduce has a wide range of real-world applications using complicated and seemingly unrelated data sets. A social networking site, for example, may utilize MapReduce to predict users’ future friends, coworkers, and other contacts based on on-site activity, names, localities, employers, and a variety of other data factors.

MapReduce may produce unique offers for each user based on their search criteria and prior behavior. An industrial facility might collect data from various sensors across the installation and utilize MapReduce to customize maintenance plans or forecast equipment breakdowns in order to increase overall uptime and cost-savings.

Alternatives and Services for MapReduce

One difficulty with MapReduce is the infrastructure required to execute it. Many organizations that may profit from big data projects lack the cash and overhead required to support such an infrastructure.

As a result, several enterprises rely on public cloud services like Hadoop and MapReduce, which provide massive scalability with low capital and maintenance expenses.

Amazon Web Services (AWS), for example, offers Hadoop as a service via its Amazon Elastic MapReduce (EMR) offering. Microsoft Azure provides the HDInsight service, which allows customers to provision Hadoop, Apache Spark, and other data processing clusters. Google Cloud Platform’s Cloud Dataproc service is used to operate Spark and Hadoop clusters.


Hadoop and MapReduce are simply one choice for enterprises that choose to construct and operate private, on-premises big data infrastructures. Other systems, including Apache Spark, High-Performance Computing Cluster, and Hydra, can be used by organizations.

The big data framework that a company chooses will be determined by the sorts of processing operations that must be performed, the available programming languages, and the performance and infrastructure requirements.

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