NoSQL Interview Questions

Introduction to NoSQL Interview Questions and Answers

NoSQL stands for ‘Not Only SQL’. NoSQL is designed for larger data sets. These databases are flexible, as they store and process unstructured, semi-structured data which are not user-friendly in handling by RDBMS. NoSQL helps in processing big data in real-time web applications. Large-scale organizations such as Google, Amazon, Facebook, etc are using NoSQL databases to handle their huge datasets.

If you are looking for a job that is related to NoSQL, you need to prepare for the 2020 NoSQL Interview Questions. Though every interview is different and the job scope is also different, we can help you out with the top NoSQL Interview Questions and Answers, which will help you take the leap and get your success in your interview.

Below is the top list of NoSQL Interview Questions and Answers. These questions are divided into two parts are as follows:

Part 1 – NoSQL Interview Questions (Basic)

This first part covers basic NoSQL interview questions and answers.

1. What do you mean by NoSQL?

Answer:

NoSQL stands for ‘Not Only SQL’, but it is also evolved due to some restrictions & challenges with the traditional databases. NoSQL databases are designed to work with large distributed data sets. NoSQL databases are highly and flexible; they allow us to store and process unstructured and semi-structured data that cannot be easily handled by using a relational database system (RDBMS). These databases are basically used for processing big data in real-time web applications.

2. What are the features of NoSQL?

Answer:

Below are some of the features of NoSQL:

• Flexibility: NoSQL offers flexibility to store structured, semi-structured or unstructured data, unlike a relational database which allows only structured data.
• Dynamic Schemas: In NoSQL, schema definition is not required; this solves the problem to modify the schema where a table is already present with huge datasets, and new columns need to be added to the same table.
• Sharding: Sharding means partitioning data into smaller databases to have faster access to data. This feature is present in NoSQL databases, allowing us to fetch data from a server in the fastest time.
• Generic: the user can customize the NoSQL database as per the need.
• Scaling: NoSQL databases scale-out horizontally; thus, they are cheaper to manage.

Let us move to the next NoSQL Interview Questions.

3. What is the CAP theorem? How is it applicable to NoSQL systems?

Answer:

This is the frequently asked NoSQL Interview Questions in an interview.CAP theorem states that there are three basic requirements for an application with distributed architecture:

• Consistency: Data in the database must be consistent before and after the execution of any operation. For example, after an update operation, every user should see the same data.
• Availability: The system should always be up and running; there should be no downtime.
• Partition Tolerance: The system should work even if the communication among the servers is unreliable.
  Theoretically, it is not possible to achieve all three requirements. CAP theorem allows distributed systems to follow any two of these requirements. Since partition tolerance is mandatory for distributed databases. Thus, we are left only with CP (Consistency, Partition tolerance) and AP (availability, Partition tolerance).
  Some of the examples of AP systems are Dynamo, Cassandra, Simple DB, CouchDB.
  Some of the examples of CP systems are Big Table, Hyper Table, Mongo DB, HBase.

4. Explain the difference: RDBMS vs NoSQL?

Answer:

RDBMS over NoSQL:

• Better for relational data that is structured and organized.
• Organize data through normalization
• Use Structured query language(SQL), which is easy to learn.
• Maintains Data Integrity
• Data and its relationships are stored in separate tables.
• ACID compliance, i.e. either all the transactions are committed or None
• Scale-up/ Vertical Scaling

NoSQL over RDBMS:

• Better for Unstructured and unpredictable Data
• Handles Big Data
• No predefined schema
• Cheaper to manage
• Scale-out/Horizontal Scaling
• BASE Transaction
• High performance, availability, and scalability

Part 2 – NoSQL Interview Questions (Advanced)

Let us now have a look at the advanced NoSQL Interview Questions.

5. What are the major challenges with traditional RDBMS?

Answer:

Following are some of the major challenges with RDBMS systems:

• Not optimized to scale out: RDBMS systems are not optimized for horizontal scaling out.
• Not able to handle unstructured data: RDBMS systems are not able to handle schema-less data (semi-structured or unstructured)
• Costly: There is a high licensing cost for data analysis with RDBMS systems.
• Not able to handle the high velocity of data ingestion: RDBMS systems are designed for steady data retention.

The NoSQL systems evolved to overcome all the above challenges.

6. What are the different types of NoSQL databases?

Answer:

There are five different categories of NoSQL databases:

• Document Database: The document databases contain many different key-value pairs. A collection contains sets of documents, and each document can contain diverse or heterogeneous fields. A document database also supports nested documents. A user can add custom fields (Dynamic data) to the document. Consider the below example:

Collection
{
personName:”Mr. X”
person phone:”1234”
personAddress:”Andheri”
}

Some of the NoSQL Document databases are Mongo DB, Couch DB etc.

• Column Database: In a column database, data is stored in cells grouped as columns rather than in the form of rows. This gives us fast retrieval and access to data. Column families contain an unlimited number of columns that can be created dynamically at runtime.
  Some of the NoSQL Column databases are Google’s Big Table, Apache Cassandra, HBase.
• Key-Value stores: It stores Hashtable of key-value pair. Hashtable contains a bucket, which is a logical group of keys. Key in Hashtable can be auto-generated or synthetic, whereas value can be String, JSON or BLOB etc. Consider the below example where a key is a city and value is an address in that city.

Some of the NoSQL Key-Value stores are:
Redis, CouchBase Server, Amazon’s Dynamo

• Cache systems: These are similar to key-value pairs. They store frequently accessed data in memory for fast retrieval and access.
  Example: Redis and Memcache
• Graph database: Graph-based databases are designed to stores information about a network of data. These are best suited for connected data. These databases represent data with edges and nodes. The edges connect nodes having some relationships, and the nodes store data.
  One of the NoSQL Graph databases is Neo4J.

Let us move to the next NoSQL Interview Questions.

7. How Does NoSQL relate to big data?

Answer:

NoSQL databases are designed with “Big Data” needs in mind. Since a fixed schema model does not bind them, this makes them suitable for today’s business needs where there is a large volume of non-uniform data (Big Data).

8. Can you explain the transaction support by using a BASE in NoSQL?

Answer:

The CAP theorem states that distributed systems cannot achieve all three properties simultaneously: consistency, availability, and partition tolerance. The BASE system gives up on consistency while maintaining the other two. The BASE system works well despite physical network partitions and always allow a client with reading and write availability.

• The BASE stands for:
  Basically Available
  Soft state
  Eventual consistency

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