HADOOP INTERVIEW GUIDE PDF
2. Hadoop Interview Questions on Page 7. Hadoop Certification Exam Simulator + Study Material o Contains 4 practice Question Paper o realistic Hadoop. hadoop interview questions hadoop, pig,hive,hbase, hdfs, mapreduce Download as PDF, TXT or read online from Scribd amadeus complete manual. Audience: Hadoop job candidates. Rating: 4. Reviewer: Ian Stirk. This Kindle- only e-book aims to help you pass an interview for a job as a.
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What is MapReduce? MapReduce is a programming model and an associated implementation for processing and generating large data sets with a parallel, distributed algorithm on a cluster.
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MapReduce jobs usually split the input data-set into independent chunks, while a Map task will process these chunks in a completely parallel manner on different nodes. The job of the framework is to sort the outputs of the maps. The reducer produces the final result with the help of the output from the previous step. Nervous about your interview? Enroll in our Big Data Hadoop course and walk into your next interview with confidence.
All the metadata information is with the Namenode and the actual data is stored on the Datanodes. Read Operation: DataFlair 1.
NameNode provides block information on which data node has the file, and the client then proceeds to read data from datanodes.
The Client reads data from all datanodes in parallel to quickly access data in case of any failure of any datanode, which is why Hadoop reads data in parallel. After the reading is complete, the connection with the datanode cluster is closed.
During reading, if the DFSInputStream encounters an error while communicating with a datanode, it will try the next closest one for that block. User asks HDFS client to write a file. The client creates the file by calling create on DistributedFileSystem. If these checks pass, the namenode makes a record of the new file; otherwise, file creation fails and the client is thrown an IOException.
As the client writes data, the DFSOutputStream splits it into packets, which it writes to an internal queue called the data queue. The data queue is consumed by the DataStreamer, which is responsible for asking the namenode to allocate new blocks by picking a list of suitable datanodes to store the replicas.
The DataStreamer streams the packets to the first datanode in the pipeline, which stores each packet and forwards it to the second datanode in the pipeline. Similarly, the second datanode stores the packet and forwards it to the third datanode in the pipeline.
The DFSOutputStream also maintains an internal queue of packets that are waiting to be acknowledged by datanodes, called the ack queue. A packet is removed from the ack queue only when it has been acknowledged by all the datanodes in the pipeline.
Edge nodes are the interface between the Hadoop cluster and the outside network. Most commonly, edge nodes are used to run client applications and cluster administration tools. Typically edge-nodes are kept separate from the nodes that contain Hadoop services such as HDFS, MapReduce, etc, mainly to keep computing resources separate.
Edge nodes running within the cluster allow for centralized management of all the Hadoop configuration entries on the cluster nodes which helps to reduce the amount of administration needed to update the config files. The fact is, given the limited security within Hadoop itself, even if your Hadoop cluster operates in a local- or wide-area network behind an enterprise firewall, you may want to consider a cluster-specific firewall to more fully protect non-public data that may reside in the cluster.
In this deployment model, think of the Hadoop cluster as an island within your IT infrastructure — for every bridge to that island you should consider an edge node for security. What Is Apache Yarn?
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Originally described by Apache as a redesigned resource manager, YARN is the next-generation computation and resource management framework in Apache Hadoop, and was introduced in Hadoop 2 to improve the MapReduce implementation, enabling Hadoop to support more varied processing approaches and a broader array of applications.
In MapReduce 1, there are two types of daemons that control the job execution process: a jobtracker and one or more tasktrackers.
The jobtracker coordinates all the jobs run on the system by scheduling tasks to run on tasktrackers. Tasktrackers run tasks and send progress reports to the jobtracker, which keeps a record of the overall progress of each job. If a task fails, the jobtracker can reschedule it on a different tasktracker. In MapReduce 1, the jobtracker takes care of both job scheduling matching tasks with tasktrackers and task progress monitoring keeping track of tasks, restarting failed or slow tasks, and doing task bookkeeping, such as maintaining counter totals.
In contrast, in YARN, these responsibilities are handled by separate entities - the resource manager and an application master one for each MapReduce job. The jobtracker is also responsible for storing job history for completed jobs; in YARN, the equivalent role is that of the timeline server, which stores application history. The namenode manages the filesystem namespace. It maintains the filesystem tree and the metadata for all the files and directories in the tree.
This information is stored persistently on the local disk in the form of two files: the namespace image, and the edit log. The namenode also knows the datanodes on which all the blocks for a given file are located; however, it does not store block locations persistently, because this information is reconstructed from datanodes when the system starts. It is also possible to run a secondary namenode, which, despite its name, does not act as a namenode.
Its main role is to periodically merge the namespace image with the edit log to prevent the edit log from becoming too large.
What is HDFS?
The secondary namenode usually runs on a separate physical machine because it requires plenty of CPU and as much memory as the namenode to perform the merge.
It keeps a copy of the merged namespace image, which can be used in the event of the namenode failing. However, the state of the secondary namenode lags behind that of the primary, so in the event of total failure of the primary, data loss is almost certain. What Is Resource Manager? The job tracker serves as both a resource manager and history server in MRv1, which limits scalability. In YARN, the job tracker's role is split between a separate resource manager and history server to improve scalability.
ResourceManager RM is the master that arbitrates all the available cluster resources and thus helps manage the distributed applications running on the YARN system. The divide-and conquer approach handles resource management and job scheduling on Hadoop systems and supports the parsing and condensing of data sets in parallel.
Thus, the ResourceManager is primarily limited to scheduling - i. The YARN equivalent of a tasktracker is a node manager. NodeManagers take instructions from the ResourceManager and manage resources available on a single node, and are therefore called per-node agents.
In contrast to a fixed number of slots for map and reduce tasks in MRV1, the NodeManager of MRV2 has a number of dynamically created resource containers. What Is Application Manager?
ApplicationMasters are responsible for negotiating resources with the ResourceManager and for working with NodeManagers to start the containers.
The main tasks of the ApplicationMaster are communicating with the ResourceManager to negotiate and allocate resources for future containers and, after container allocation, communicating with NodeManagers to launch application containers on them. The Application Manager is the actual owner of the job. As the Application Manager is launched within a container that may share a physical host with other containers, given the multi-tenancy nature, amongst other issues, it cannot make any assumptions of things like pre-configured ports that it can listen on.
What Is A Container? A deployed container runs as an individual process on a slave node in a Hadoop cluster. What Is WritableComparable? WritableComparator is a general-purpose implementation of RawComparator for WritableComparable classes. IntWritable implements the WritableComparable interface, which is just a subinterface of the Writable and java. Comparable interfaces: package org.
NullWritable is a special type of Writable, as it has a zero-length serialization. No bytes are written to or read from the stream. It is used as a placeholder; anything writing or reading NullWritables will know ahead of time that it will be dealing with that type. NullWritable can also be useful as a key in a SequenceFile when you want to store a list of values, as opposed to key-value pairs. The Context object allows the mapper to interact with the rest of the Hadoop eco-system.
It includes configuration data for the job, as well as interfaces that allow it to deliver output. The context objects are used for emitting key-value pairs.
The new API makes extensive use of context objects that allow the user code to communicate with the MapReduce system.
What Is A Mapper? Maps are the individual tasks that transform input records into intermediate records. The transformed intermediate records do not need to be of the same type as the input records. A given input pair may map to zero or to many output pairs. Explain The Shuffle MapReduce makes the guarantee that the input to every reducer is sorted by key. The process by which the system performs the sort — and transfers the map outputs to the reducers as inputs — is known as the shuffle.
Input to the Reducer is the sorted output of the mappers. About Curriculum Fees Request Info. Get our detailed course curriculum. Know all the top Hadoop Interview Questions and their Answers.
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Download the Hadoop Interview Questions and Answers pdf. Hadoop Interview Preparation. Self-Paced Course. Solve Sample Hadoop Interview Questions The instructor will solve and provide answers to the latest Hadoop interview questions on programming, scenario based and real-time.
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Crack the toughest Hadoop programming interview questions Hadoop interviews are tough and the interview questions will get progressively tougher for experienced professionals.
Know the latest Hadoop interview questions, tips and tricks to solve them Hadoop is an evolving technology. What if I have any doubts? For any doubt clearance, you can use: Discussion Forum - Assistant faculty will respond within 24 hours Phone call - Schedule a 30 minute phone call to clear your doubts Skype - Schedule a face to face skype session to go over your doubts. Do you provide placements?When the work is completed, the JobTracker updates its status.
Usually I never comment on blogs but your article is so convincing that I never stop myself to say something about it. I hope it will help a lot for all.
I hope you will post some more information about the software. Answer: Note that HDFS is known to support exclusive writes processes one write request for a file at a time only. Keep sharing this gainful articles and continue updating us. WritableComparable objects can be compared to each other using Comparators.
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