Interview Questions.

Q1. What is Hadoop?

Ans: Hadoop is a allotted computing platform. It is written in Java. It consist of the functions like Google File System and MapReduce.

Q2. What platform and Java model is required to run Hadoop?

Ans: Java 1.6.X or higher model are properly for Hadoop, ideally from Sun. Linux and Windows are the supported working device for Hadoop, but BSD, Mac OS/X and Solaris are greater famous to work.

Q3. What are the most commonplace Input Formats in Hadoop?

Ans:

Text Input Format: Default input format in Hadoop.

Key Value Input Format: used for simple textual content documents wherein the files are damaged into strains.

Sequence File Input Format: used for analyzing documents in sequence.

Q4. What is SSH?

Ans: Secure Shell additionally known as as Secure Socket Shell.

Q5. What is Hadoop Map Reduce?

Ans: For processing huge data units in parallel throughout a hadoop cluster, Hadoop MapReduce framework is used.  Data evaluation makes use of a -step map and decrease method.

Q6. What kind of Hardware is best for Hadoop?

Ans: Hadoop can run on a twin processor/ dual core machines with four-eight GB RAM the usage of ECC reminiscence. It depends on the workflow wishes.

Q7. What is Sequence File in Hadoop?

Ans: Extensively used in Map Reduce I/O codecs, Sequence File is a flat report containing binary key/value pairs. The map outputs are saved as Sequence File internally. It gives Reader, Writer and Sorter classes. The three Sequence File codecs are:

Uncompressed key/cost information.

Record compressed key/value statistics – most effective ‘values’ are compressed here.

Block compressed key/value statistics – each keys and values are accumulated in ‘blocks’ one at a time and compressed. The size of the ‘block’ is configurable.

Q8. What is the Use of SSH in Hadoop?

Ans: We ought to use SSH in Hadoop due to the fact SSH is a integrated username and password schema that may be used for secure get entry to to a faraway host; it is a more secure opportunity to rlogin and telnet.

Q9. What is Name Node in Hadoop?

Ans: Name Node in Hadoop is in which Hadoop shops all the report area information in HDFS. It is the master node on which task tracker runs and includes metadata.

Q10. How Hadoop Map Reduce works?

Ans: In MapReduce, in the course of the map segment it counts the words in every document, while within the lessen segment it aggregates the information as in keeping with the record spanning the entire collection. During the map section the input statistics is divided into splits for evaluation via map duties running in parallel across Hadoop framework.

Q11. What is Input Block in Hadoop? Explain.

Ans: When a Hadoop activity runs, it blocks input documents into chunks and assign each cut up to a mapper for processing. It is known as Input block.

Q12. How will layout the HDFS?

Ans: $hadoop namenode –format

Q13. Mention what are the main configuration parameters that user need to specify to run Map lessen Job?

Ans: 

The consumer of Map lessen framework needs to specify

Job’s enter locations in the allotted document gadget

Job’s output place in the dispensed file device

Input layout

Output format

Class containing the map function

Class containing the reduce function

JAR report containing the mapper, reducer and motive force instructions

Q14. How many Input blocks is made by means of a Hadoop Framework?

Ans: The default block size is 64MB, in keeping with which, Hadoop will make five Block as following:

One Block for 64K documents

Two Block for 65MB documents, and

Two Block for 127MB documents

The block length is configurable.

Q15. How are you able to debug Hadoop code?

Ans: First, take a look at the listing of Map Reduce jobs currently going for walks. Next, we want to look that there are not any orphaned jobs strolling; if yes, you want to determine the region of RM logs.

Run: “playstation  grep –I Resource Manager”

and look for log directory inside the displayed result. Find out the task-id from the displayed list and take a look at if there's any errors message related to that job.

On the basis of RM logs, perceive the employee node that changed into concerned in execution of the undertaking.

Now, login to that node and run – “ps –ef mistakes come from person degree logs for every map-lessen process.

Q16. Mention what is the Hadoop MapReduce APIs settlement for a key and fee class?

For a key and cost elegance, there are two Hadoop MapReduce APIs agreement:

The cost need to be defining the org.Apache.Hadoop.Io.Writable interface

The key need to be defining the org.Apache.Hadoop.Io.WritableComparable interface

Q17. What is the usage of RecordReader in Hadoop?

Ans: Input Block is assigned with a work but does not recognize how to get admission to it. The file holder magnificence is completely responsible for loading the information from its source and convert it into keys pair suitable for analyzing via the Mapper. The RecordReader's instance may be defined by the Input Format.

Q18. How to compress mapper output but not the reducer output?

Ans: To obtain this compression, you must set:

conf.Set("mapreduce.Map.Output.Compress", real)

conf.Set("mapreduce.Output.Fileoutputformat.Compress", false)

Q19. What is Hive?

Ans: Hive is a statistics warehouse software program that's used for enables querying and dealing with big records units dwelling in distributed garage.

Q20. List out Hadoop’s 3 configuration files?

Ans: The three configuration files are:

core-web page.Xml

mapred-website online.Xml

hdfs-website.Xml

Q21. What is JobTracker in Hadoop?

Ans: JobTracer is a provider inside Monitors and assigns Map duties and Reduce responsibilities to corresponding challenge tracker at the facts nodes

Q22. What are real-time enterprise applications of Hadoop?

Ans: Hadoop, properly referred to as Apache Hadoop, is an open-source software platform for scalable and dispensed computing of huge volumes of facts. It provides rapid, high performance and price-powerful evaluation of established and unstructured data generated on digital platforms and inside the organisation. It is used in almost all departments and sectors today.Some of the instances wherein Hadoop is used:

Managing site visitors on streets.

Streaming processing.

Content Management and Archiving Emails.

Processing Rat Brain Neuronal Signals the use of a Hadoop Computing Cluster.

Fraud detection and Prevention.

Advertisements Targeting Platforms are using Hadoop to capture and examine click move, transaction, video and social media information.

Managing content, posts, photographs and videos on social media structures.

Analyzing patron data in real-time for improving commercial enterprise overall performance.

Public zone fields such as intelligence, protection, cyber safety and medical studies.

Financial corporations are using Big Data Hadoop to reduce danger, analyze fraud patterns, pick out rogue buyers, more exactly goal their marketing campaigns based totally on client segmentation, and enhance patron pleasure.

Getting get entry to to unstructured records like output from medical devices, health practitioner’s notes, lab outcomes, imaging reviews, medical correspondence, medical statistics, and monetary information.

Q23. What is Hive Metastore ?

Ans: Hive Meta shop is a database that shops metadata of your hive tables like table name,column name,information kinds,table place,variety of buckets in the desk and many others.

Q24. Mention what's the Hadoop MapReduce APIs agreement for a key and price elegance?

Ans: For a key and cost class, there are two Hadoop MapReduce APIs contract:

The cost ought to be defining the org.Apache.Hadoop.Io.Writable interface

The key have to be defining the org.Apache.Hadoop.Io.WritableComparable interface

Q25. What are the functionalities of JobTracker?

Ans: These are the primary tasks of JobTracker:

To accept jobs from consumer.

To talk with the NameNode to decide the location of the data.

To locate TaskTracker Nodes with to be had slots.

To put up the paintings to the selected TaskTracker node and monitors progress of every tasks.

Q26. What is Hive Present Version?

Ans: hive-0.Thirteen.1

Q27. What are the middle methods of a Reducer?

Ans: The three center techniques of a Reducer are:

setup(): this technique is used for configuring numerous parameters like enter records length, allotted cache.

Public void setup (context)

lessen(): coronary heart of the reducer continually known as as soon as in step with key with the related reduced undertaking

public void lessen(Key, Value, context)

cleanup(): this technique is referred to as to smooth temporary files, most effective as soon as at the quit of the project

public void cleanup (context)

Q28. For the use of Hadoop list the network requirements?

Ans: For the usage of Hadoop the list of community requirements are:

Password-less SSH connection.

Secure Shell (SSH) for launching server procedures.

Q29. What is Hadoop Streaming?

Ans: Hadoop streaming is a software which permits you to create and run map/reduce task. It is a accepted API that allows programs written in any languages to be used as Hadoop mapper.

Q30. Can i get entry to Hive Without Hadoop ?

Ans: Yes,We can get entry to Hive with out hadoop with the help of different data storage systems like Amazon S3, GPFS (IBM) and MapR record device .