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The Ultimate Cheat Sheet On Hadoop

Top 20 frequently asked questions to test your Hadoop knowledge given in the below Hadoop cheat sheet. Try finding your own answers and match the answers given here.




Question #1 

You have written a MapReduce job that will process 500 million input records and generate 500 million key-value pairs. The data is not uniformly distributed. Your MapReduce job will create a significant amount of intermediate data that it needs to transfer between mappers and reducers which is a potential bottleneck. A custom implementation of which of the following interfaces is most likely to reduce the amount of intermediate data transferred across the network?



A. Writable
B. WritableComparable
C. InputFormat
D. OutputFormat
E. Combiner
F. Partitioner
Ans: e




Question #2 

Where is Hive metastore stored by default ?


A. In HDFS
B. In client machine in the form of a flat file.
C. In client machine in a derby database
D. In lib directory of HADOOP_HOME, and requires HADOOP_CLASSPATH to be modified.
Ans: c




Question…

5 top Data Storage Patterns to handle variety of data

Data is now a variety of patterns. Data is now more than just plain text, it can exist in various persistence-storage mechanisms, with Hadoop distributed file system (HDFS) being one of them.

The way data is ingested or the sources from which data is ingested affects the way data is stored. On the other hand, how the data is pushed further into the downstream systems or accessed by the data access layer decides how the data is to be stored.

Role of RDBMS

The need to store huge volumes of data has forced databases to follow new rules of data relationships and integrity that are different from those of relational database management systems (RDBMS). RDBMS follow the ACID rules of atomicity, consistency, isolation, and durability.

These rules make the database reliable to any user of the database. However, searching huge volumes of big data and retrieving data from them would take large amounts of time if all the ACID rules were enforced.
A typical scenario is when we search for a certain topic using Google. The search returns innumerable pages of data; however, only one page is visible or basically available (BA). 
The rest of the data is in a soft state (S) and is still being assembled by Google, though the user is not aware of it. By the time the user looks at the data on the first page, the rest of the data becomes eventually consistent (E). This phenomenon—basically available soft state and eventually consistent—is the rule followed by the big data databases, which are generally NoSQL databases following BASE properties.

Database theory suggests that any distributed NoSQL big database can satisfy only two properties predominantly and will have to relax standards on the third. 

The three properties are consistency, availability, and partition tolerance (CAP). This is the CAP theorem. 

Polyglot pattern: Multiple types of storage mechanisms—like RDBMS, file storage, CMS, OODBMS, NoSQL, and HDFS—co-exist in an enterprise to solve the big data problem.

The aforementioned paradigms of ACID, BASE, and CAP give rise to new big data storage patterns like below:
  • Faรงade pattern: HDFS serves as the intermittent Faรงade for the traditional DW systems. 
  • Lean pattern: HBase is indexed using only one column-family and only one column and unique row-key. 
  • NoSQL pattern: Traditional RDBMS systems are replaced by NoSQL alternatives to facilitate faster access and querying of big data.

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