PouchDB Interview Questions and Answers for 10 years experience

1. What is PouchDB and how does it differ from CouchDB?

   • Answer: PouchDB is a JavaScript database that is an isomorphic version of CouchDB. It provides the same API as CouchDB, but it runs entirely in the browser (or in Node.js). The key difference is that PouchDB is client-side, syncing with a CouchDB server (or another PouchDB instance) when connectivity is available, whereas CouchDB is a full-fledged server-side database.

2. Explain the concept of replication in PouchDB.

   • Answer: Replication in PouchDB is the process of synchronizing data between a local PouchDB instance and a remote database (typically CouchDB or another PouchDB instance). It allows changes made on one database to be reflected on the other, ensuring data consistency across multiple devices or locations. Replication can be one-way or two-way, and can be configured to handle conflicts using different strategies.

3. How does PouchDB handle conflicts during replication?

   • Answer: PouchDB provides mechanisms to handle conflicts that arise when the same document is modified on multiple databases simultaneously. The default conflict resolution strategy is to create a new revision of the document with both conflicting changes, tagged as a conflict. More sophisticated conflict resolution strategies can be implemented by using custom conflict handlers that define how to merge or resolve the conflicting revisions based on specific criteria.

4. Describe different replication strategies in PouchDB.

   • Answer: PouchDB offers various replication strategies: One-way replication (push or pull), continuous replication (real-time syncing), and bidirectional replication (changes in either direction are synced). The choice depends on application requirements, such as the need for immediate consistency, bandwidth considerations, and the frequency of updates.

5. What are the advantages of using PouchDB over other client-side databases like IndexedDB?

   • Answer: PouchDB offers a simpler, more familiar API based on CouchDB's RESTful approach, making it easier to learn and use, especially for developers already familiar with CouchDB. Its replication capabilities significantly simplify data synchronization across multiple devices and servers, a feature not natively offered by IndexedDB. PouchDB also abstracts away many of the complexities of IndexedDB, handling data persistence and conflict resolution more seamlessly.

6. Explain the role of revisions in PouchDB.

   • Answer: Revisions in PouchDB track the history of changes made to a document. Each change generates a new revision, allowing for rollback capabilities and conflict resolution. This ensures data integrity and the ability to trace changes over time. Revisions are crucial for replication and conflict handling.

7. How do you handle large datasets in PouchDB?

   • Answer: Handling large datasets efficiently in PouchDB requires strategies like data partitioning, efficient querying (using indexes), and potentially using a remote CouchDB server for storage and bulk operations. Chunking large documents and using the `_bulk_docs` API for bulk operations can improve performance. Careful consideration of data modeling and query optimization is vital.

8. How can you optimize PouchDB performance?

   • Answer: Performance optimization in PouchDB includes using appropriate indexes, minimizing the size of documents, using bulk operations (`_bulk_docs`), and efficiently handling replication (e.g., setting appropriate filter functions). Choosing the right replication strategy (continuous vs. periodic) based on application requirements is also critical. Profiling and analyzing queries can pinpoint bottlenecks.

9. What are the different ways to query data in PouchDB?

   • Answer: PouchDB offers various querying mechanisms. The simplest is using `find()` with JSON selectors for simple queries. More complex queries can be achieved using `allDocs` with startkey, endkey, and key parameters for range-based queries. For highly optimized queries, creating indexes using the `createIndex` method is crucial for faster lookups.

10. Explain the use of design documents and views in PouchDB.

    • Answer: Design documents in PouchDB (though less crucial than in CouchDB due to limitations in browser environments) define views which enable efficient querying. A view is a pre-defined query that is stored within the database and can be executed more rapidly than a runtime query. Although views aren't as performant in PouchDB as they are in CouchDB, they can still be helpful for certain types of frequently-used queries.

11. Describe your experience with PouchDB and its integration with other technologies (e.g., React, Angular, Node.js).

    • Answer: [Detailed answer describing specific projects and technologies used, highlighting challenges and solutions]

12. How would you handle data security in a PouchDB application?

    • Answer: [Detailed answer describing security measures, such as HTTPS for replication, encryption of data at rest and in transit, and authentication mechanisms]

13. Explain your experience with PouchDB's different storage adapters.

    • Answer: [Detailed answer about experience with IndexedDB, WebSQL, and other adapters, highlighting advantages and disadvantages of each]

14. How have you used PouchDB for offline-first web applications?

    • Answer: [Detailed answer describing how offline capabilities were implemented, including conflict resolution strategies and syncing mechanisms]

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