Top 56 MongoDB Interview Questions & Answers (2026)

01 What is MongoDB? 02 What is a document in MongoDB? 03 What is a collection in MongoDB? 04 What is BSON? 05 What is the difference between MongoDB and a relational database? 06 How do you insert documents in MongoDB? 07 How do you query documents in MongoDB? 08 How do you update documents in MongoDB? 09 How do you delete documents in MongoDB? 10 What is the ObjectId in MongoDB? 11 What are indexes in MongoDB? 12 What is the aggregation pipeline in MongoDB? 13 What is the $lookup stage in MongoDB aggregation? 14 What is a replica set in MongoDB? 15 What is MongoDB sharding? 16 What is the difference between embed and reference in MongoDB schema design? 17 What are MongoDB data types? 18 What is the MongoDB query language and how does it differ from SQL? 19 How does MongoDB handle transactions? 20 What is the MongoDB Atlas? 21 What is MongoDB Compass? 22 What is the oplog in MongoDB? 23 What are change streams in MongoDB? 24 What is GridFS in MongoDB? 25 What is the explain() method in MongoDB? 26 What is the difference between find() and aggregate() in MongoDB? 27 What are TTL indexes in MongoDB? 28 What is a sparse index in MongoDB? 29 What is the MongoDB wire protocol? 30 What is a compound index and when should you use it?

01 What is the MongoDB aggregation pipeline optimization? 02 What is MongoDB's write concern? 03 What is MongoDB's read concern? 04 What are partial indexes in MongoDB? 05 What is the MongoDB aggregation $bucket and $bucketAuto stage? 06 How does MongoDB handle schema validation? 07 What is the $facet stage in MongoDB aggregation? 08 What is the difference between $project and $addFields in MongoDB? 09 What are multikey indexes in MongoDB? 10 What is the MongoDB profiler? 11 What is the WiredTiger storage engine? 12 What is MongoDB's approach to concurrency? 13 What is the difference between $unwind and $lookup in MongoDB? 14 What is the aggregation $group stage and its accumulator operators? 15 How does MongoDB handle geospatial data? 16 What is the MongoDB connection string format? 17 What is the MongoDB aggregation $expr operator?

01 How does MongoDB replication work internally? 02 How does MongoDB sharding distribute data internally? 03 What is the WiredTiger cache and how does it affect performance? 04 What is the Aggregation $setWindowFields stage? 05 How does MongoDB handle index builds on large collections? 06 What is the MongoDB Aggregation $merge and $out stage? 07 What are MongoDB Atlas Search and Vector Search? 08 How do you optimize MongoDB query performance? 09 What is the MongoDB Aggregation Framework's $graphLookup stage?