Hadoop Basic Interview Questions and Answer

Question: Name fews companies that use Hadoop?

Facebook
Amazon
Twitter
eBay
Adobe
Netflix
Hulu
Rubikloud

Question: Differentiate between Structured and Unstructured data?
Data which are proper categorized and easily search and update is know as Structured data.
Data which are proper un-categorized and can't search and update easily is know as Un-Structured data.

Question: On Which concept the Hadoop framework works?
HDFS: Hadoop Distributed File System is the java based file system for scalable and reliable storage of large datasets. Data in HDFS is stored in the form of blocks and it operates on the Master Slave Architecture.
Hadoop MapReduce:MapReduce distributes the workload into various tasks which runs in parallel. Hadoop jobs perform 2 separate job. The map job breaks down the data sets into key-value pairs or tuples. The reduce job then takes the output of the map job & combines the data tuples in smaller set of tuples. The job is performed after the map job is executed.

Question: What is Hadoop streaming?
Hadoop distribution has a generic programming interface for writing the code in any programming language like PHP, Python, Perl, Ruby etc is know as Hadoop Streaming.

Question: What is block and block scanner in HDFS?
Block: The minimum amount of data that can be read or written is know as "block" (Defualt 64MB).
Block Scanner tracks the list of blocks present on a DataNode and verifies them to find any type of checksum errors.

Question: What is commodity hardware?
Hadoop have thousands of commodity hardware which are inexpensive that do not have high availability. these are used to execute to job.

Can we write MapReduce in other than JAVA Language?
Yes, you can write MapReduce task in other languages like PHP, Perl etc.

Question: What are the primary phases of a Reducer?

Shuffle
Sort
Reduce

Question: What is Big Data?
Big data is too heavy database that exceeds the processing capacity of traditional database systems.

Question: What is NoSQL?
It is non-relational un-structured database.

Question: What problems can Hadoop solve?
It sove following problems.

When database too heavy and exceed its limit.
Reduce the cost of server.

Question:Name the modes in which Hadoop can run?
Hadoop can be run in one of three modes:

Standalone (or local) mode
Pseudo-distributed mode
Fully distributed mode

Question:What is the full form of HDFS?
Hadoop Distributed File System

Question:What is DataNode and Namenode in Hadoop?
Namenode is the node which stores the filesystem metadata.
File maps with block locations are stored in datanode.

Question:What are the Hadoop configuration files?