CouchDB Interview Questions and Answers for freshers

1. What is CouchDB?

   • Answer: CouchDB is a NoSQL, document-oriented database. It stores data in JSON documents and uses HTTP as its API. It's known for its simplicity, scalability, and ease of use, particularly for applications requiring flexibility and rapid development.

2. What are the key features of CouchDB?

   • Answer: Key features include its JSON document storage, RESTful HTTP API, built-in replication capabilities, versioning, and map-reduce functionality for querying data.

3. How does CouchDB differ from relational databases?

   • Answer: Unlike relational databases which use tables and schemas, CouchDB stores data in JSON documents without a predefined schema. This offers greater flexibility but requires different querying techniques (like map-reduce).

4. Explain the concept of a document in CouchDB.

   • Answer: A document in CouchDB is a JSON object with key-value pairs. It's the fundamental unit of data storage. Documents are self-contained and can have different structures.

5. What is a view in CouchDB?

   • Answer: A view is a pre-defined query on your data. It uses map and reduce functions to process documents and generate a result set. Views are created and updated independently, improving query performance.

6. Explain the Map and Reduce functions in CouchDB.

   • Answer: Map functions iterate over documents and emit key-value pairs. Reduce functions aggregate the emitted values from the map function based on the keys.

7. What is replication in CouchDB?

   • Answer: Replication allows you to synchronize data between multiple CouchDB instances. It ensures data consistency across different servers or locations, providing high availability and fault tolerance.

8. How does CouchDB handle data consistency?

   • Answer: CouchDB uses a combination of techniques, including versioning and conflict resolution mechanisms, to maintain data consistency. Replication helps synchronize changes across multiple databases.

9. What are the different types of replication in CouchDB?

   • Answer: There are push and pull replication. Push replication sends data from a source database to a target database. Pull replication retrieves data from a source database to a target database.

10. Explain the concept of revisions in CouchDB.

    • Answer: Each document in CouchDB has a revision history. Each update creates a new revision, allowing you to track changes and revert to previous versions if necessary.

11. How do you handle conflicts in CouchDB?

    • Answer: CouchDB detects conflicts when multiple changes are made to the same document simultaneously. You can resolve these conflicts manually or by defining custom conflict resolution strategies.

12. What are design documents in CouchDB?

    • Answer: Design documents contain views, lists, shows, and updates – functions that define how your data is accessed and manipulated. They are crucial for querying and manipulating data.

13. What is Futon?

    • Answer: Futon is a web-based administration interface for CouchDB. It allows you to manage databases, view documents, and perform other administrative tasks.

14. What is Fauxton?

    • Answer: Fauxton is a newer, more modern web-based administration interface for CouchDB, offering improved usability and features compared to Futon.

15. How do you perform a query in CouchDB?

    • Answer: Queries are typically performed using views defined in design documents. You specify the view name and any necessary parameters in the HTTP request.

16. What are some common use cases for CouchDB?

    • Answer: CouchDB is suitable for applications like content management systems, real-time collaboration tools, mobile applications, and applications requiring offline capabilities due to its replication features.

17. How can you secure CouchDB?

    • Answer: Security measures include using strong passwords, enabling authentication mechanisms (like user roles and permissions), and securing the network access to the CouchDB server.

18. What are some of the limitations of CouchDB?

    • Answer: Limitations include its relatively less mature ecosystem compared to relational databases and potentially slower performance for complex joins or transactions which are not its strong suit.

19. Explain the concept of attachments in CouchDB.

    • Answer: Attachments are binary files (images, documents, etc.) that can be stored directly within a CouchDB document. They are base64 encoded within the document.

20. How do you handle large documents in CouchDB?

    • Answer: For very large documents, consider breaking them down into smaller, more manageable documents or using alternative storage mechanisms for the binary data (like external file systems) and referencing them in the CouchDB document.

21. What are some popular CouchDB clients?

    • Answer: Popular clients include the official CouchDB client libraries available for various programming languages like Python, JavaScript, Java, etc.

22. How can you perform data validation in CouchDB?

    • Answer: Data validation can be done using validation functions within design documents. These functions are executed before a document is saved, allowing you to enforce rules and constraints on the data.

23. Explain the use of _id and _rev in CouchDB documents.

    • Answer: `_id` is the unique identifier for a document. `_rev` is the revision identifier, used to track changes and handle conflicts.

24. What is the role of the `_design` document?

    • Answer: The `_design` document prefix is used to identify documents that contain views, shows, lists, and update handlers.

25. How can you back up a CouchDB database?

    • Answer: You can perform backups by copying the database directory or using tools to create database snapshots and replicating the database to another server.

26. What is the difference between a view and a query in CouchDB?

    • Answer: A view is a pre-defined query stored in a design document for faster querying. A query is a request made at runtime using the view.

27. How does CouchDB handle schema changes?

    • Answer: Because CouchDB is schema-less, schema changes don't require downtime or complex migration processes. You can simply add or remove fields in your JSON documents without affecting other documents.

28. What is a CouchDB cluster?

    • Answer: A CouchDB cluster is a collection of CouchDB nodes working together to provide high availability and scalability. It typically uses a distributed approach to data storage.

29. How do you manage user authentication in CouchDB?

    • Answer: CouchDB offers built-in mechanisms for user authentication and authorization using users and roles. You can configure access control lists to restrict access to databases and documents.

30. What are some tools used for CouchDB development?

    • Answer: Tools include Futon/Fauxton (admin UI), various client libraries, and command-line tools for managing databases.

31. What is the purpose of the `_changes` feed in CouchDB?

    • Answer: The `_changes` feed provides a stream of notifications about changes (insertions, updates, deletions) made to a database. It's useful for building real-time applications.

32. Explain the concept of continuous replication in CouchDB.

    • Answer: Continuous replication keeps the target database continuously updated with changes from the source database as they occur. This ensures near real-time synchronization.

33. How do you handle security in a CouchDB cluster?

    • Answer: Security measures in a cluster involve managing user authentication and authorization across all nodes, secure network configuration between nodes, and proper database replication settings.

34. What are some performance optimization techniques for CouchDB?

    • Answer: Optimizations include using efficient view design, indexing relevant fields, optimizing map and reduce functions, and properly managing database replication.

35. How do you troubleshoot common CouchDB issues?

    • Answer: Troubleshooting involves checking logs, using the Futon/Fauxton UI to monitor database status, checking network connectivity, and examining replication status.

36. What is the role of the `_local` documents in CouchDB?

    • Answer: `_local` documents are only stored on the local database and are not replicated.

37. How do you perform bulk document uploads in CouchDB?

    • Answer: Bulk uploads can be done using the CouchDB API's `_bulk_docs` endpoint, allowing efficient insertion of multiple documents in a single request.

38. What is the difference between a document and an attachment?

    • Answer: A document is the primary unit of data (JSON). An attachment is a binary file associated with a document, stored as base64 within it.

39. What is the significance of the `_deleted` field?

    • Answer: The `_deleted` field is used to mark a document as deleted. Even though deleted, the revision history is retained.

40. Explain the concept of CouchDB's security model.

    • Answer: CouchDB uses a Role-Based Access Control (RBAC) model with users and roles to manage access to databases and documents.

41. How do you create a new database in CouchDB?

    • Answer: You create a new database using HTTP PUT request to the `/dbname` endpoint.

42. How do you delete a document in CouchDB?

    • Answer: You delete a document using HTTP DELETE request to the document's `_id` endpoint, including its `_rev`.

43. How do you update a document in CouchDB?

    • Answer: You update a document using HTTP PUT request to the document's `_id` endpoint, including the new JSON data and the current `_rev`.

44. What is a CouchDB filter?

    • Answer: A filter is a JavaScript function that allows more complex document selection compared to views, before the map function is executed.

45. How do you configure SSL/TLS for CouchDB?

    • Answer: SSL/TLS configuration requires setting up certificates and configuring CouchDB to use them; typically involving changes to the `local.ini` file.

46. What are some alternatives to CouchDB?

    • Answer: Alternatives include MongoDB, Cassandra, and other NoSQL databases depending on specific requirements.

47. What is the difference between CouchDB and Cloudant?

    • Answer: Cloudant is a managed CouchDB service offered by IBM Cloud. It provides the functionalities of CouchDB but as a hosted solution.

48. How do you monitor the performance of a CouchDB server?

    • Answer: Monitoring involves using the built-in statistics, checking logs, and using external monitoring tools.

49. What are some best practices for designing CouchDB applications?

    • Answer: Best practices include proper database design, efficient view design, utilizing replication strategies, and implementing robust security measures.

50. How can you improve the scalability of a CouchDB application?

    • Answer: Scalability can be improved by using CouchDB clusters, optimizing views and queries, employing appropriate replication strategies, and using load balancing techniques.

51. What are some common errors you might encounter while working with CouchDB?

    • Answer: Common errors include document conflicts, database access issues, replication failures, and view index errors.

52. How do you handle updates to design documents in CouchDB?

    • Answer: Updating design documents involves using HTTP PUT to update the document while making sure to use the correct `_rev`.

53. How does CouchDB handle concurrency?

    • Answer: CouchDB handles concurrency using multi-version concurrency control (MVCC), ensuring that conflicting updates are detected and handled appropriately using revision IDs.

54. Explain the importance of indexing in CouchDB.

    • Answer: Indexing enhances the speed of queries, particularly for views. Properly chosen indexes significantly improve performance.

55. What are some ways to optimize the performance of views?

    • Answer: Optimization includes using appropriate map and reduce functions, choosing relevant keys, and using indexes effectively.

56. How do you integrate CouchDB with other systems?

    • Answer: Integration happens through the REST API and client libraries. It can be used as a backend for various applications and platforms.

57. What is the role of the `_security` document?

    • Answer: The `_security` document defines the security settings for a database, including users, roles, and their permissions.

58. How do you test CouchDB applications?

    • Answer: Testing includes using unit tests for code, integration tests to verify database interactions, and end-to-end tests to cover the entire application flow.

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