CouchDB Interview Questions and Answers for experienced

1. What is CouchDB?

   • Answer: CouchDB is a NoSQL, document-oriented database. It stores data in JSON documents and uses an HTTP API for access. It's known for its simplicity, scalability, and ease of use, particularly in situations where schema flexibility is paramount.

2. Explain the concept of "documents" in CouchDB.

   • Answer: In CouchDB, documents are self-contained JSON objects. Each document has a unique ID and can contain any number of key-value pairs. This flexible schema allows for easy adaptation to evolving data structures.

3. What is a revision in CouchDB?

   • Answer: Every time a document is updated in CouchDB, a new revision is created. Revisions are tracked using unique identifiers, allowing for easy rollback to previous versions if needed. This ensures data integrity and enables version control.

4. How does CouchDB handle concurrency?

   • Answer: CouchDB uses multi-version concurrency control (MVCC). Multiple users can update a document simultaneously, and CouchDB manages these updates by tracking revisions. Conflicts are resolved through custom conflict resolution functions or by manually choosing a winning revision.

5. Explain the role of views in CouchDB.

   • Answer: Views provide a way to query and index data in CouchDB. They are defined using MapReduce functions, allowing for complex data aggregation and transformation. Views are pre-computed for faster query execution.

6. What are MapReduce functions in CouchDB?

   • Answer: MapReduce is a programming model for processing large datasets. In CouchDB, Map functions iterate over documents and emit key-value pairs, while Reduce functions aggregate these pairs to produce summarized results.

7. Describe the difference between a Map function and a Reduce function.

   • Answer: The Map function processes each document individually and emits key-value pairs. The Reduce function takes the emitted key-value pairs and aggregates them, often summarizing the data (e.g., counting, summing).

8. What is replication in CouchDB?

   • Answer: Replication allows you to synchronize data across multiple CouchDB databases. This enables high availability, data backup, and distribution of data across geographically dispersed locations.

9. Explain different replication types in CouchDB.

   • Answer: CouchDB supports various replication types, including push, pull, and bidirectional replication. Push replication pushes changes from one database to another, pull replication pulls changes from one database to another, and bidirectional replication keeps two databases synchronized in both directions.

10. How do you handle conflicts during replication?

    • Answer: Conflicts during replication are handled using conflict resolution strategies. This can involve custom conflict resolution functions, manual intervention, or choosing a winning revision based on timestamps or other criteria.

11. What is a CouchDB design document?

    • Answer: A design document is a special type of document that stores views, shows, lists, updates, and other auxiliary information. It is used to organize and manage queries and other database operations.

12. Explain the role of _design documents in CouchDB.

    • Answer: _design documents contain the logic for views, which are used to query and index data. They centralize the query logic, making it easier to manage and maintain.

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

    • Answer: A new database is created using an HTTP PUT request to the CouchDB server's base URL with the database name appended (e.g., `PUT /mydb`).

14. How do you delete a database in CouchDB?

    • Answer: A database is deleted using an HTTP DELETE request to the CouchDB server's base URL with the database name appended (e.g., `DELETE /mydb`).

15. How do you query data in CouchDB?

    • Answer: Data is queried using views defined in design documents. You send an HTTP GET request to a specific view URL to retrieve the query results.

16. What are some common use cases for CouchDB?

    • Answer: CouchDB is well-suited for applications requiring high availability, scalability, and flexible schema, such as real-time collaboration tools, mobile applications, and applications needing offline capabilities.

17. What are the advantages of using CouchDB?

    • Answer: Advantages include its simplicity, ease of use, scalability, built-in replication, and flexible schema.

18. What are the disadvantages of using CouchDB?

    • Answer: Disadvantages can include limitations in complex join operations compared to relational databases, and potential challenges in managing large schemas without careful design.

19. How does CouchDB handle attachments?

    • Answer: CouchDB allows you to store attachments (files) within documents. Attachments are base64 encoded and stored as part of the document.

20. Explain the concept of security in CouchDB.

    • Answer: CouchDB offers role-based access control (RBAC) to manage user permissions. You can define roles with specific permissions, and assign these roles to users to control access to databases and documents.

21. How do you implement authentication and authorization in CouchDB?

    • Answer: Authentication and authorization are usually handled through external authentication mechanisms like Apache or Nginx, or via CouchDB's built-in authentication system, often using an external authentication provider.

22. What are some tools for managing and monitoring CouchDB?

    • Answer: Fauxton (the CouchDB web interface), command-line tools like `curl` or specialized CouchDB clients, and monitoring tools like Grafana or Prometheus can be used.

23. How do you perform a bulk upload of documents into CouchDB?

    • Answer: Bulk uploads can be done using the `_bulk_docs` API endpoint, which allows for efficient insertion of multiple documents in a single request.

24. Explain the use of Futon in CouchDB.

    • Answer: Futon is the older web-based administration interface for CouchDB. While Fauxton is now preferred, Futon can still be found in older installations.

25. How do you handle schema changes in CouchDB?

    • Answer: Because CouchDB is schema-less, schema changes are handled naturally; you simply add or remove fields in your JSON documents as needed. However, you might need to update your views to accommodate these changes.

26. What are some best practices for designing CouchDB databases?

    • Answer: Best practices include careful design of views for efficient querying, appropriate use of indexes, and understanding how document structure affects query performance.

27. How do you perform backups and restores in CouchDB?

    • Answer: Backups are often performed through replication to a separate database, or by using tools to copy the database files. Restores involve copying the backup files or replicating from the backup database.

28. Explain the concept of indexing in CouchDB.

    • Answer: Indexing in CouchDB happens implicitly through the creation of views. The Map function of a view essentially defines the index, which is used to speed up queries.

29. What are some common performance tuning techniques for CouchDB?

    • Answer: Techniques include optimizing view design, ensuring proper indexing, using efficient query patterns, and adjusting server resources.

30. How do you troubleshoot common CouchDB issues?

    • Answer: Troubleshooting involves checking logs, examining error messages, using the Fauxton/Futon interface for diagnostics, and potentially utilizing tools like top or htop to monitor system resource utilization.

31. What is the difference between CouchDB and other NoSQL databases like MongoDB or Cassandra?

    • Answer: CouchDB focuses on document-oriented storage with built-in replication and MVCC. MongoDB also uses documents but has a more complex query language and different replication mechanisms. Cassandra is a wide-column store better suited for high-throughput, distributed systems.

32. Explain the role of the `_id` field in a CouchDB document.

    • Answer: The `_id` field is a unique identifier for each document in CouchDB. It's automatically generated if not provided, ensuring uniqueness across the database.

33. What is the role of the `_rev` field in a CouchDB document?

    • Answer: The `_rev` field stores the revision ID of the document, allowing CouchDB to track changes and manage concurrent updates.

34. How do you update a document in CouchDB?

    • Answer: To update a document, you send an HTTP PUT request with the updated JSON document and its `_rev` field. CouchDB uses the `_rev` field to identify the document to be updated and create a new revision.

35. How do you delete a document in CouchDB?

    • Answer: To delete a document, you send an HTTP DELETE request, providing the document's `_id` and `_rev` fields. This marks the document as deleted and creates a new revision reflecting the deletion.

36. Explain the concept of attachments in CouchDB and how they are stored.

    • Answer: Attachments are binary files associated with a document. They are base64 encoded and stored within the document itself, unlike separate file systems. This makes them portable and easily manageable alongside document data.

37. How do you access attachments in CouchDB?

    • Answer: Attachments are accessed via HTTP GET requests, specifying the document ID and attachment name in the URL.

38. What are some considerations when choosing between using CouchDB and a relational database?

    • Answer: Consider schema flexibility (CouchDB excels here), data relationships (relational databases are better for complex relationships), transaction requirements (relational databases offer ACID properties), and query complexity.

39. Describe the different types of indexes available in CouchDB.

    • Answer: CouchDB primarily uses implicit indexes created through views. These are essentially B-tree indexes optimized for the specific queries defined in the view's map function. There aren't other explicit index types as in some other databases.

40. How can you improve the performance of queries in CouchDB?

    • Answer: Optimize view design for the queries you'll be running frequently, ensuring appropriate use of keys in the map function. Also, reduce the amount of data processed by the reduce function (if used) and use appropriate filtering techniques.

41. Explain the concept of continuous replication in CouchDB.

    • Answer: Continuous replication constantly monitors the source database for changes and replicates them to the target database as soon as they occur, maintaining near real-time synchronization.

42. How do you handle large documents in CouchDB?

    • Answer: For very large documents, consider breaking them down into smaller, more manageable documents to improve performance. You could use related documents linked by IDs.

43. What are some techniques for scaling CouchDB?

    • Answer: CouchDB can be scaled horizontally by adding more nodes to the cluster, leveraging its distributed nature and replication capabilities.

44. Explain how to use CouchDB with other technologies.

    • Answer: CouchDB integrates well with various technologies via its RESTful HTTP API. You can use it with various programming languages (e.g., Python, Node.js, Java) and frameworks.

45. What are some common security considerations when deploying CouchDB in a production environment?

    • Answer: Secure the CouchDB server itself (firewall, strong passwords), manage user authentication and authorization carefully, enable SSL/TLS encryption, and regularly update the CouchDB software.

46. How do you monitor the health and performance of a CouchDB cluster?

    • Answer: Use monitoring tools (like those mentioned earlier) to track CPU usage, memory consumption, disk I/O, and replication status. Examine CouchDB's logs for errors and warnings.

47. Describe your experience working with CouchDB in a team environment.

    • Answer: [This requires a personal answer based on your experience. Describe your role, the team's workflow, collaboration methods, and any challenges or successes you encountered.]

48. What are some advanced features of CouchDB that you have used?

    • Answer: [This requires a personal answer. Mention any advanced features you've used, such as complex view designs, custom conflict resolution functions, or advanced security configurations.]

49. Explain your approach to designing a scalable and robust CouchDB application.

    • Answer: [This requires a personal answer. Describe your design process, including considerations for data modeling, view design, replication, and error handling. Mention any design patterns or best practices you follow.]

50. How would you handle a situation where data corruption occurs in a CouchDB database?

    • Answer: [This requires a personal answer. Describe your troubleshooting steps, including checking logs, examining replication status, restoring from backups, and using any available diagnostic tools.]

51. What are some of the limitations of CouchDB, and how would you work around them?

    • Answer: [This requires a personal answer. Discuss limitations like join operations, complex transactions, and then describe workarounds, like pre-aggregating data in views or using external processing for complex joins.]

52. Describe your experience with CouchDB's security features and how you've used them to protect sensitive data.

    • Answer: [This requires a personal answer. Detail your experience with roles, permissions, authentication, authorization, and encryption measures used in your CouchDB applications.]

53. How do you stay up-to-date with the latest developments and best practices in CouchDB?

    • Answer: [This requires a personal answer. Mention resources like the official CouchDB website, community forums, blogs, conferences, and any relevant newsletters or mailing lists you follow.]

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