CouchDB Interview Questions and Answers for 7 years experience

CouchDB Interview Questions & Answers (7 Years Experience)
  1. What is CouchDB and how does it differ from traditional relational databases?

    • Answer: CouchDB is a NoSQL, document-oriented database. Unlike relational databases which use tables and schemas, CouchDB stores data in JSON documents. It emphasizes ease of use, scalability, and high availability. Key differences include its schema-less nature, allowing flexible data modeling, and its use of MapReduce for querying instead of SQL. It also typically replicates data across multiple nodes for fault tolerance.
  2. Explain the concept of revisions in CouchDB.

    • Answer: CouchDB maintains a history of all changes to a document through revisions. Each update creates a new revision with a unique ID, preserving the document's history. This allows for conflict resolution, rollback to previous versions, and understanding the evolution of data.
  3. Describe CouchDB's replication mechanism.

    • Answer: CouchDB uses a pull-replication model where databases replicate changes from a source database to a target database. It can be configured to replicate continuously or on a schedule. It handles conflicts using a last-write-wins or custom conflict resolution strategies. Push replication is also possible, using external tools.
  4. How does CouchDB handle concurrent updates to a document?

    • Answer: Concurrent updates are managed through revisions. If multiple users update the same document simultaneously, CouchDB assigns each update a new revision. Conflicts are detected when a document is updated based on an outdated revision. The database can be configured to handle conflicts using last-write-wins or a custom conflict resolution function.
  5. What are views in CouchDB and how are they used?

    • Answer: Views are pre-defined queries that are stored in the database. They provide an efficient way to query data without scanning all documents. They are defined using MapReduce functions; the map function emits key-value pairs, and the reduce function aggregates these pairs. Views are indexed, enabling fast querying.
  6. Explain the concept of MapReduce in CouchDB.

    • Answer: MapReduce is a programming model for processing large datasets. In CouchDB, the map function processes each document individually, emitting key-value pairs. The reduce function then aggregates these key-value pairs, performing calculations like summing, averaging, or counting.
  7. What are design documents in CouchDB?

    • Answer: Design documents contain views, lists, shows, and updates, enabling structured access to data within a database. They are ordinary JSON documents with a special identifier that starts with `_design/`.
  8. How do you handle security in CouchDB?

    • Answer: Security in CouchDB is managed through roles and access control lists (ACLs). You can define roles with specific permissions and assign them to users or groups. ACLs specify which users or roles have read, write, or other access to specific databases or documents.
  9. Explain the difference between _all_docs and a view.

    • Answer: `_all_docs` returns all documents in a database, whereas views provide indexed and filtered access. Views are far more efficient for querying large datasets because they avoid scanning every document. `_all_docs` is useful for simple scans or when views aren't defined.

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