25 Top NoSQL Interview Questions and Answers (2024)
Blog / 25 Top NoSQL Interview Questions and Answers (2024)
NoSQL (Not Only SQL), refers to a category of database management systems that differ from traditional relational database systems (RDBMS) in several significant ways.
Knowing the fundamentals about NoSQL databases is great way to stand out in interviews.
This blog will teach you the most up to date NoSQL interview questions and will help you nail your next interview.
What is NoSQL?
Junior
- NoSQL (Not Only SQL), refers to a category of database management systems that differ from traditional relational database systems (RDBMS) in several significant ways.
- These systems are designed to handle a wide variety of data models, including key-value, document, columnar, and graph formats.
What are the key characteristics of NoSQL?
Junior
- Schema Flexibility: Dynamic schema for unstructured data, allowing changes without affecting existing data.
- Scalability: Designed to scale out by distributing data across multiple servers, ideal for large-scale data processing.
- High Performance: Optimized for specific data models and access patterns, offering efficient operations like key-value lookups and document retrievals.
- Data Model Variety: Supports a range of data models including document, key-value, columnar, and graph.
- Distributed Nature: Built for distributed environments, spreading data across multiple machines for resilience.
- High Availability: Techniques like replication and partitioning ensure high availability and fault tolerance.
- Non-Relational: Uses various models other than the traditional relational one, avoiding fixed table schemas and join operations.
- Ease of Development: Simplified management and more natural data models for developers.
- Big Data Support: Suitable for big data applications due to their capacity to handle large volumes of data efficiently.
- Multi-Model Support: Some systems support different data models within the same database engine.
What are the main differences between NoSQL and traditional relational databases?
Junior
- Data Model: Relational databases use structured, table-based models; NoSQL uses varied models like key-value, document, columnar, and graph.
- Schema Flexibility: Relational databases require a fixed schema; NoSQL offers schema flexibility.
- Scalability: Relational databases traditionally scale vertically (enhancing a single server); NoSQL is designed for horizontal scalability (across many servers).
- Query Language: SQL is used in relational databases; NoSQL employs various querying languages and APIs.
- Transaction Support: Relational databases support strong ACID properties; NoSQL may have weaker consistency models for better performance.
- Consistency and Reliability: Relational databases focus on strong consistency; NoSQL emphasizes high availability and partition tolerance.
- Use Cases: Relational databases are ideal for complex queries and transactional integrity; NoSQL is better for large, diverse data sets and scalable applications.
- Data Integrity: Relational databases enforce data integrity with constraints; NoSQL relies more on application-level data integrity.
Explain the CAP theorem in the context of NoSQL databases.
Junior
- The CAP theorem, in the context of NoSQL databases, states that a distributed database system can only simultaneously provide two out of the following three properties:
- Consistency: Every read receives the most recent write or an error.
- Availability: Every request receives a response, without guarantee of it containing the most recent write.
- Partition Tolerance: The system continues to operate despite network partitions.
What does it mean for a NoSQL database to be "AP," "CP," or "CA"?
Junior
- AP (Availability and Partition Tolerance): The system prioritizes availability and partition tolerance, meaning it remains operational and accessible despite network failures, but may not always provide the most recent data (consistency can be compromised).
- CP (Consistency and Partition Tolerance): The system ensures data consistency and operates despite partitions, but may sacrifice availability (not all requests are guaranteed a response).
- CA (Consistency and Availability): This combination is less common in distributed systems, as it implies the system maintains data consistency and availability but may not handle network partitions effectively. In practice, a true CA system is hard to achieve in a distributed environment.
Don't Let One Question Ruin Your Interview...
Explain the BASE acronym in NoSQL databases.
Junior
- BASE stands for Basically Available, Soft state, Eventually consistent
- Basically Available: The system guarantees availability in terms of being able to perform read and write operations.
- Soft State: The state of the system may change over time, even without input, due to eventual consistency.
- Eventual Consistency: The system will become consistent over time, given that no new updates are made to the data.
What are the common types of NoSQL databases?
Junior
- Document-Oriented: Stores data in document-like structures (e.g., JSON, XML). Example: MongoDB.
- Key-Value Stores: Simple, uses key-value pairs for storage. Example: Redis.
- Column-Family Stores: Stores data in columns rather than rows. Example: Cassandra.
- Graph Databases: Designed for data represented as graphs. Example: Neo4j.
Explain the characteristics and use cases of a document-oriented NoSQL database.
Mid
- Characteristics:
- Store data in document formats like JSON or XML.
- Schema-flexible, allowing varied and nested data structures.
- Index and query capabilities based on document attributes.
- Use Cases:
- Handling semi-structured or unstructured data.
- Applications requiring rapid development and iteration.
- Content management systems, e-commerce applications, and situations where each record can be unique.
Explain the characteristics and use cases of a Key-Value Stores NoSQL database.
Mid
- Characteristics of Key-Value Stores NoSQL Database:
- Simple Data Model: Data is stored as key-value pairs, where a unique key is associated with a value.
- High Performance: Optimized for quick retrieval and storage, offering fast read/write operations.
- Scalability: Easily scalable, often used for distributed storage systems.
- Limited Query Capabilities: Typically, they support basic operations like get, put, and delete based on keys.
- Use Cases:
- Session Storage: Ideal for storing user session data in web applications.
- Caching: Frequently used for high-speed caching solutions.
- Real-Time Recommendations: Used in scenarios requiring quick data access, like real-time recommendation engines.
- User Profiles and Preferences: Suitable for storing and retrieving user-specific information.
Explain the characteristics and use cases of a Column-Family Stores NoSQL database.
Mid
- Characteristics of Column-Family Stores NoSQL Database:
- Column-Oriented Storage: Data is stored in columns instead of rows, optimizing for read/write of specific data subsets.
- Scalability: Highly scalable for large datasets and distributed systems.
- Flexible Schema: Allows variation in columns across different rows.
- Efficient Queries: Optimized for queries over large datasets and aggregation operations.
- Use Cases:
- Big Data Analytics: Suitable for handling and analyzing large volumes of data.
- Time-Series Data: Ideal for time-stamped data like IoT data, financial data, or event logging.
- Content Management Systems: Useful for managing content with variable attributes.
- Recommendation Engines: Efficient for processing user behavior and preferences for recommendations.
Explain the characteristics and use cases of a Graph Databases NoSQL database.
Mid
- Characteristics of Graph Databases NoSQL Database:
- Graph Structure: Data is stored as nodes (entities), edges (relationships), and properties.
- Relationship-First Approach: Optimized for handling complex relationships and network structures.
- Flexible Schema: Adaptable to various data models, accommodating evolving structures.
- Efficient Relationship Queries: Excellent for traversing and querying interconnected data.
- Use Cases:
- Social Networks: Ideal for managing complex and dynamic social connections.
- Recommendation Systems: Effective in suggesting content based on user relationships and preferences.
- Fraud Detection: Useful in detecting patterns and relationships indicative of fraudulent activities.
- Network and IT Operations: Applicable for mapping and analyzing network topologies and dependencies.
Explain the concept of eventual consistency in distributed NoSQL databases.
Mid
- Eventual consistency in distributed NoSQL databases refers to a model where database updates are propagated across nodes over time, meaning all nodes will eventually hold the same data, but not necessarily immediately.
- This approach improves availability and performance at the cost of immediate data consistency.
What is a composite key in NoSQL databases, and why might you use it in data modelling?
Mid
- A "composite key" in NoSQL databases is a key formed by combining two or more attributes to create a unique identifier for each record. It is used in data modeling to efficiently access and query data, particularly in scenarios where data is organized by more than one attribute, enhancing query performance and enabling more complex data relationships.
- For example, in an e-commerce application, a composite key might include a product's category and SKU to ensure uniqueness across categories.
Explain the concept of consistent hashing in the context of distributed NoSQL databases.
Mid
- Consistent Hashing is a technique used to distribute data evenly across multiple nodes or partitions in a distributed database. It ensures that when a node is added or removed, only a minimal amount of data needs to be relocated.
- Consistent Hashing is important for load balancing and maintaining data distribution in a dynamic and scalable environment.
What is document-level locking in NoSQL databases.
Mid
- Document-level locking in NoSQL databases is a mechanism that locks individual documents during transactions to prevent concurrent modifications, ensuring data integrity and consistency. This granular approach allows multiple operations to occur in parallel while avoiding conflicts and data corruption.
What are secondary indexes in NoSQL databases?
Mid
- Secondary indexes in NoSQL databases are additional indexes created on non-primary key attributes, allowing efficient querying and retrieval of data based on those attributes. They enhance search performance on fields other than the primary key.
Explain the concept of denormalization in NoSQL databases.
Mid
- Denormalization in NoSQL databases refers to the practice of intentionally combining data from multiple tables into a single, larger table.
- This reduces the need for complex joins, improving read performance and scalability, but can increase data redundancy and storage requirements.
What is write amplification in the context of NoSQL databases?
Mid
- Write amplification in NoSQL databases refers to the phenomenon where the amount of data physically written to storage is significantly more than the logical data size being written.
- This occurs due to database background processes like compaction and replication, impacting storage efficiency and write performance.
- Techniques to mitigate write amplification include batch processing, write-ahead logs, and compaction strategies.
Explain the concept of offline-first applications and how NoSQL databases can support them.
Mid
- Offline-first applications are designed to work seamlessly both online and offline, with data synchronization when connectivity is restored.
- NoSQL databases can support offline-first applications by:
- Local Data Storage: Embedding within the application to store data locally, enabling functionality without internet connectivity.
- Data Synchronization: Efficiently syncing local data with the server once online, handling conflicts and data merging.
- Flexible Data Models: Adapting to varied data structures, useful for changes during offline use.
- Scalability and Performance: Providing quick data access and updates for a responsive user experience in offline mode.
- Conflict Resolution: Managing concurrent updates and data inconsistencies between offline and online states.
What is a Bloom filter?
Senior
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Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
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Explain the concept of compensating transactions in NoSQL databases.
Senior
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Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Explain the concept of distributed locking in NoSQL databases.
Senior
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Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
What is materialized view in NoSQL databases?
Senior
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Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Discuss the advantages and disadvantages of using NoSQL databases for time-series data storage.
Senior
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Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Name some NoSQL databases suitable for time-series data.
Senior
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Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.