avatarSomal Chakraborty


(Part 2) MongoDB Challenges Senior Developers Are Solving

Scenario 1–5 are covered in Part 1 of this article

In the second part of this article, we would go through some challenges and frequently asked interview questions about MongoDB. Each challenge would start with a scenerio describing the problem statement, which would follow up with an answer and finally explaining the terminologies used in the question and answer. If you’re not familiar with some terminology used, the Terminology section after the Answer section is for you. Feel free to read the problem statement, take a pause, answer on your own and then look at the answer. Ready? let’s roll !

Scenario 6 (Field Level Encryption):

You want to implement field-level encryption in MongoDB to secure sensitive data. How would you configure and use MongoDB’s encryption features?


  • Enable encryption at rest using MongoDB’s encryption options.
  • Use the encrypt field level in the schema to encrypt specific fields.
  • Manage encryption keys securely using MongoDB’s key management features.


  • Field Level Encryption: Field-level encryption in MongoDB secures sensitive data by encrypting specific fields. For example, encrypt a ‘creditCard’ field in a ‘users’ collection, ensuring only authorised users can access the encrypted data:
  • Enable encryption at rest: Utilize MongoDB’s encryption options to secure data at rest. For example, use the WiredTiger storage engine with encryption settings. This ensures that data stored on disk is encrypted, adding a layer of protection against unauthorized access even if physical storage media are compromised.
  • Encrypt specific fields: Implement field-level encryption in the schema to protect sensitive information.
  • Secure key management: Safely manage encryption keys using MongoDB’s built-in key management features.

Scenario 7 (Geospatial Index):

Problem: You need to create a geospatial index in MongoDB for efficient querying of location-based data. How would you implement and use geospatial indexes?


  • Create a 2dsphere index on the field containing location data.
  • Use the $geoNear stage in aggregation pipelines for geospatial queries.
  • Leverage geospatial operators like $near or $within for specific queries.


  • Geospatial Index: A geospatial index is a special type of index used in databases to efficiently support queries involving spatial data, such as geographical coordinates (latitude and longitude). This type of index enables the database to perform geometric operations and quickly retrieve data based on proximity or location
  • Create 2dsphere index: Build a geospatial index on the location data field for efficient querying.
  • Use $geoNear in aggregation: Employ the $geoNear stage in aggregation pipelines for geospatial queries. This operator calculates and returns documents based on proximity to a specified point. For instance, db.places.aggregate([{ $geoNear: { near: { type: "Point", coordinates: [longitude, latitude] }, distanceField: "distance" } }]) retrieves places near a specific location, including the distance
  • Leverage geospatial operators: Apply operators like $near or $within for specific geospatial queries. Using $near finds locations close to a specified point, enhancing efficiency in locating nearby places. The $within operator in MongoDB’s geospatial queries determines if a location is within a specified geometric shape, such as a polygon or circle

Scenario 8 (Data Isolation):

Problem: You want to ensure data isolation between different clients in a multi-tenant MongoDB environment. How would you design the database to achieve this?


  • Use a separate database or namespace for each client or tenant.
  • Implement access controls and user roles to restrict access to each client’s data.
  • Consider sharding to further isolate data if the number of clients grows significantly.


  • Multi-tenant MongoDB environment : A multi-tenant MongoDB environment refers to a setup where a single MongoDB database serves multiple independent clients or tenants, keeping their data isolated and secure. Each client has its own set of collections or namespaces within the shared database.
  • Separate databases/namespaces: Ensure data isolation by assigning each client or tenant a distinct database or namespace.
  • Access controls and roles: Implement user roles and access controls to restrict data access for each client.
  • Consider sharding: Sharding in MongoDB involves horizontally partitioning data across multiple servers or shards to distribute the workload and scale horizontally. For instance, a ‘users’ collection could be sharded based on a shard key like ‘username,’ distributing user data across shards for improved performance and scalability in a large-scale application.

Scenario 9 (Optimize Storage):

Problem: Your MongoDB deployment is encountering storage space issues. How would you optimize storage and manage disk space efficiently?


  • Use the compact command to reclaim disk space by defragmenting collections.
  • Implement compression at the storage level to reduce data size.
  • Monitor and manage the size of indexes, removing unnecessary or unused indexes.


  • Compact command: Reclaim disk space by defragmenting collections using the compact command.
  • Compression at storage level: Reduce data size by implementing compression at the storage level. By configuring compression options, MongoDB compresses data on disk, reducing storage space requirements
  • Monitor and manage indexes: Keep track of index sizes, removing unnecessary or unused indexes to optimise storage.

Scenario 10 (Text Search Feature):

Problem: Your MongoDB application requires text search capabilities, and you want to optimize search performance. How would you configure and use MongoDB’s text search features?


  • Create a text index on the fields you want to search.
  • Use the $text operator in queries to perform text searches.
  • Configure the text index to include or exclude specific words or languages based on your application needs.


  • Create text index: Enable text search capabilities by creating a text index on relevant fields.
  • Use $text operator: Perform optimized text searches using the $text operator in queries. For instance, to find documents containing the word “example,” use a query like db.collection.find({ $text: { $search: "example" } }). This leverages MongoDB's text indexes, improving search performance for text-based queries in the specified collection.
  • Configure text index: Tailor the text index to include or exclude specific words or languages based on application requirements. For instance, customise the text index to focus on relevant terms like “keyword” and disregard common words such as “and” for optimised text searches.

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