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Answer:- MongoDB is a NoSQL, document-oriented database that stores data in BSON format (Binary JSON).
Answer:- MongoDB is a NoSQL document-oriented database, meaning it stores data as JSON-like documents instead of tables and rows.
Answer:-
Answer:- BSON (Binary JSON) is MongoDB’s binary-encoded JSON format used for storing documents efficiently.
Answer:- A collection is a group of related documents, similar to a table in relational databases.
Answer:- Use db command.
Answer:- A document is a JSON-like object that stores data as key-value pairs.
Answer:-
Answer:-Run the command: mongod
Answer:- Run
Answer:- mongod –version
Answer: db.collection.insertOne({“name”: “Alice”, “age”: 25}
Answer: db.collection.insertMany([{“name”: “Bob”}, {“name”: “Charlie”}])
Answer: db.collection.find()
Answer: db.collection.find({“age”: 25})
Answer: db.collection.updateOne({“name”: “Alice”}, {“$set”: {“age”: 26}})
Answer: db.collection.updateMany({}, {“$set”: {“status”: “active”}})
Answer: db.collection.deleteOne({“name”: “Alice”})
Answer: db.collection.deleteMany({“age”: {“$lt”: 18}})
Answer: db.collection.drop()
Answer: db.dropDatabase()
Answer:An index improves query performance by speeding up data retrieval
Answer:db.collection.createIndex({name: 1})
Answer:db.collection.getIndexes()
Answer:db.collection.dropIndex({name: 1})
Answer: A compound index is an index on multiple fields, e.g., db.collection.createIndex({name: 1, age: -1})
Answer: A powerful tool for data analysis and transformation in MongoDB
Answer: db.collection.aggregate([ { “$match”: { “age”: { “$gt”: 20 } } } ])
Answer: It groups documents and applies aggregation operations like sum, avg, etc
Answer: It sorts documents, e.g., db.collection.aggregate([ { “$sort”: { “age”: -1 } } ])
Answer: It limits the number of returned documents, e.g., db.collection.aggregate([ { “$limit”: 5 } ])
Answer: Using embedded documents (denormalization) or references (normalization)
Answer: Storing related data inside a single document
Answer: Storing related data separately and linking using ObjectIds
Answer: A process to ensure data availability by maintaining multiple copies of data
Answer:A group of MongoDB servers that maintain copies of the same data.
Answer: Embedding is better for one-to-few relationships, referencing for one-to-many.
Answer: A method to distribute large datasets across multiple servers.
Answer: The node that handles write operations.
Answer: A node that replicates data from the primary node
Answer: rs.status()
Answer: Start MongoDB with –auth and create users.
Answer: db.createUser({user: “admin”, pwd: “password”, roles: [“readWrite”]})
Answer: Roles define permissions, e.g., “read”, “readWrite”, “dbAdmin”, etc.
Answer: Use: mongodump –db mydb –out /backup/path
Answer: Use: mongorestore /backup/path
Answer: A system for storing large files, such as images and videos.
Answer: 27017
Answer: db.stats()
Answer: db.collection.stats()
Answer:- MongoDB is a NoSQL database with flexible schemas, while MySQL is a relational database using
structured tables
Answer:- Scalability, flexible schema, high availability, and horizontal scaling through sharding.
Answer:- A fixed-size collection that automatically overwrites oldest documents when it reaches the limit.
Answer:- db.createCollection(‘log’, {capped: true, size: 100000})
Answer:- An ObjectId in MongoDB is 12 bytes long.
Answer:- db.collection.find({ fieldName: { $exists: true } })
Answer:- To perform pattern matching on string fields.
Answer:- Use the dot notation: db.collection.updateOne({ ‘user.name’: ‘Alice’ }, { $set: { ‘user.age’: 30 } })
Answer:- find() returns multiple documents, while findOne() returns a single document.
Answer:-Matches documents where an array field contains all specified values.
Answer:- Use the $regex operator with ‘i’ option: db.collection.find({ name: { $regex: ‘john’, $options: ‘i’ } })
Answer: It matches documents containing an array field with elements that meet multiple criteria.
Answer: db.collection.updateMany({}, { $rename: { ‘oldField’: ‘newField’ } })
Answer: $push adds an element to an array, while $addToSet adds only if it doesn’t already exist.
Answer: db.collection.updateOne({}, { $pull: { arrayField: value } })
Answer: db.collection.countDocuments()
Answer: db.getCollectionNames().includes(‘collectionName’)
Answer:A document left behind after a shard migration in sharded clusters.
Answer: An index on multiple fields; useful when queries filter or sort by multiple fields.
Answer: db.collection.createIndex({ email: 1 }, { unique: true })
Answer: $group groups documents, while $project reshapes documents by including/excluding fields.
Answer: It uniquely identifies a document; automatically indexed.
Answer: Using the $lookup aggregation stage.
Answer: db.collection.updateOne({}, { $inc: { count: 1 } })
Answer: db.collection.distinct(‘fieldName’)
Answer: Provides execution details of a query to optimize performance.
Answer: A query that can be satisfied using only an index without reading documents.
Answer: db.collection.createIndex({ name: ‘text’ })
Answer: db.collection.find({ $text: { $search: ‘keyword’ } })
Answer: Allows multiple aggregation pipelines to run in a single query.
Answer: A cloud database service for managing MongoDB clusters.
Answer: A feature that allows real-time monitoring of changes in a collection.
Answer: db.collection.watch()
Answer: A way to ensure atomicity across multiple documents using transactions.
Answer: session.startTransaction()
Answer: session.abortTransaction()
Answer: Storing large files, such as images and videos, in MongoDB.
Answer: db.collection.find().sort({ field: -1 }).limit(1)
Answer:A special collection that records all changes in a replica set.
Answer: db.stats()
Answer: It is the default MongoDB storage engine, providing better performance and concurrency.
Answer: Enable profiling with db.setProfilingLevel(1) and check system.profile collection.
Answer: Use the –enableEncryption option when starting MongoDB
Answer: Allows encryption of specific fields without encrypting the entire database.
Answer: Create users with specific roles using db.createUser().
Answer: Enable sharding with sh.enableSharding(‘databaseName’) and shard a collection with
sh.shardCollection().
Answer: A router that directs client requests to the appropriate shard in a sharded cluster.
Answer: db.serverStatus().connections
Answer: rs.printSlaveReplicationInfo()
Answer:An election process selects a new primary node.
Answer:- Replica sets provide redundancy and high availability, while sharding distributes data across
multiple servers for scalability.
Answer:- Through read and write concerns, journaling, and replication
Answer:- Majority waits for acknowledgment from most replica set members, while Local acknowledges after
writing to the primary node.
Answer:- Using multi-document ACID transactions introduced in MongoDB 4.2.
Answer:- The oplog (operations log) is a capped collection that records all changes in a replica set for
replication.
Answer:- Single field, compound, multikey, text, hashed, wildcard, and geospatial indexes.
Answer:- Through document-level locking and WiredTiger’s multi-version concurrency control (MVCC).
Answer:- $merge writes results to an existing collection, while $out replaces an entire collection with results.
Answer:- It redistributes data across shards to ensure balanced load.
Answer:- By selecting a good shard key that evenly distributes data and query load.
Answer:- The process of moving data between shards when rebalancing the cluster.
Answer: Using sh.status(), db.serverStatus(), and the MongoDB Atlas performance monitoring tools.
Answer: A secondary node that does not serve read queries and is used for backup or analytics.
Answer: To influence the election process of a primary node.
Answer: By building the new index in the background and then dropping the old one after validation.
Answer: It improves performance by managing memory allocation between MongoDB and the OS.
Answer: Using the –auditDestination parameter to log user operations.
Answer: Ensures a transaction reads a consistent snapshot of the database, used in multi-document
transactions
Answer: Occurs when a primary node steps down before its writes are replicated, causing data reversion.
Answer: A secondary node with a replication delay to maintain historical versions of data.
Answer: By enabling database profiling and checking the system.profile collection.
Answer: A member of a replica set that participates in elections but does not store data
Answer: By stepping down the primary using rs.stepDown().
Answer: Backup config servers and shards separately, then restore in order: config servers first, then shards.
Answer: Provides real-time performance statistics of a MongoDB instance.
Answer: Use indexes, limit the use of $lookup, and apply $match early in the pipeline.
Answer: collStats provides statistics on a collection, while dbStats gives database-level metrics.
Answer: By ensuring queries use indexes and avoiding regex searches without indexing.
Answer: Queries for that shard’s data will fail unless the cluster is configured for partial results.
Answer: By running db.collection.find({ shardKey: { $exists: false } }).
Answer: Allows automatic retry of write operations in case of transient failures.
Answer: By checking rs.printSlaveReplicationInfo() and monitoring network latency.
Answer: An index-building strategy that allows both foreground and background indexing approaches.
Answer: Restart the instance with –replSet and initialize the replica set using rs.initiate().
Answer: Determines how queries route to replica set members (e.g., primary, secondary, nearest).
Answer: By checking db.serverStatus().metrics.document and WiredTiger cache stats.
Answer: Uses an external LDAP service for user authentication.
Answer: Using db.collection.stats().
Answer: Ensures durability by logging write operations before applying them to data files.
Answer: fsync flushes data to disk, while journaling writes changes to a log before applying them.
Answer: Using mongodump/mongorestore or MongoDB Atlas live migration.
Answer: Randomly selects a specified number of documents from a collection.
Answer: UUID is a standard 128-bit unique identifier, while ObjectId is a 12-byte MongoDB-specific identifier.
Answer: Nodes vote based on priority and replication lag, and the node with the most votes becomes the
new primary
Answer: A technique to ensure atomicity in distributed transactions using commit and abort phases.
Answer: Using TTL indexes to automatically delete documents after a specified time.
Answer: Returns documents in the order they were stored in memory or disk.
Answer: By checking db.currentOp() and lock statistics in db.serverStatus().
Answer: Monitors the time spent reading and writing data per collection.
Answer: Use write concerns, backups, and require confirmation for bulk delete operations
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