back end developer Interview Questions and Answers

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100 Backend Developer Interview Questions and Answers

  1. What is the difference between REST and GraphQL?

    • Answer: REST (Representational State Transfer) and GraphQL are both architectural styles for building APIs, but they differ significantly. REST uses a resource-based approach, where each resource has a unique URL and uses HTTP methods (GET, POST, PUT, DELETE) to interact with it. It often involves multiple requests to fetch related data. GraphQL, on the other hand, is a query language that allows clients to specify exactly the data they need in a single request. This reduces over-fetching and under-fetching common in REST APIs. REST is generally simpler to implement, while GraphQL offers greater flexibility and efficiency for complex data fetching scenarios.

  2. Explain the concept of ACID properties in database transactions.

    • Answer: ACID properties ensure database transactions are processed reliably. They stand for: Atomicity (all operations succeed or none do), Consistency (data remains consistent with defined rules), Isolation (concurrent transactions don't interfere with each other), and Durability (committed data survives system failures). These properties guarantee data integrity even in the face of errors or concurrent access.

  3. What are different types of database indexing techniques?

    • Answer: Several indexing techniques exist, each with trade-offs. B-tree indexes are common for ordered data, allowing efficient lookups, insertions, and deletions. Hash indexes offer fast lookups based on hash values but are less efficient for range queries. Full-text indexes are optimized for searching text data. Spatial indexes are designed for geographic data. The choice of index depends on the query patterns and data characteristics.

  4. What is the difference between SQL and NoSQL databases?

    • Answer: SQL (Structured Query Language) databases use a relational model with structured schemas and tables, enforcing data integrity through relationships. They're excellent for structured data and transactional consistency. NoSQL databases offer various data models (document, key-value, graph, etc.) and are more flexible and scalable for unstructured or semi-structured data, often prioritizing availability and partition tolerance over strict consistency.

  5. Describe different ways to handle concurrency in a multi-threaded application.

    • Answer: Concurrency control mechanisms prevent data corruption and race conditions in multi-threaded applications. These include: mutexes (mutual exclusion locks), semaphores (managing access to resources), monitors (high-level synchronization constructs), and atomic operations (indivisible operations). Proper choice depends on the application's needs and complexity.

  6. Explain the concept of caching and its benefits.

    • Answer: Caching stores frequently accessed data in a faster, readily available location (e.g., RAM) to reduce database or network latency. Benefits include improved application performance, reduced server load, and better user experience. However, cache invalidation strategies must be carefully considered to ensure data consistency.

  7. What are different message queues and their use cases?

    • Answer: Message queues (e.g., RabbitMQ, Kafka, ActiveMQ) facilitate asynchronous communication between different parts of an application or between different services. Use cases include decoupling services, handling high volumes of messages, providing fault tolerance, and enabling real-time processing.

  8. How do you handle errors and exceptions in your backend code?

    • Answer: Robust error handling is crucial. Techniques include using try-catch blocks to catch exceptions, logging errors for debugging and monitoring, implementing custom exception classes for specific error types, and returning appropriate HTTP status codes to clients to indicate success or failure. Centralized error logging and monitoring systems are also essential.

  9. What are different authentication and authorization mechanisms?

    • Answer: Authentication verifies the identity of a user (e.g., username/password, OAuth 2.0, JWT). Authorization determines what resources a user is allowed to access. Common authorization methods include role-based access control (RBAC) and attribute-based access control (ABAC).

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