Technologies Coding Problems Bookmarks Learning Paths

Technologies Coding Problems Bookmarks Learning Paths

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Questions

9 of 15

1How to find a shard key?

2What is refining a shard key and how to do it?

3How to reshard a collection?

4What are different sharding strategies?

5What is Shard?

6What are advantages of Sharding?

7What are the components of a sharded cluster?

8Discuss Vertical and Horizontal scaling?

9What is sharding in MongoDB?

10How to shard a collection?

11What is a shard key?

12How do we chose a shard key?

13What are zones in sharding?

14Is it possible to change a document's shard key value and how?

15What is primary shard?

MongoDB

Bulk Operations

09 / 15

What is sharding in MongoDB? | Sharding | MongoDB Interview Questions | NextRound.in

What is sharding in MongoDB?

Difficulty: 6/10

shard key selection, balancing, cluster migration

Sharding is a method for distributing data across multiple machines by partitioning data into smaller chunks (shards). MongoDB uses sharding to support deployments with very large data sets and high throughput operations.

Scenario Questions

0-2 years experience

1We have a small e‑commerce app that stores the product catalog in a single MongoDB instance. If we want to start using sharding to handle growth, which steps would you take to enable sharding for the 'products' collection?
2Suppose you set the shard key to 'category' and insert a new document with a category value that doesn't exist yet. What happens during the insert on a sharded cluster?
3If a query filters only by 'price' and the collection is sharded on 'category', how will MongoDB route that query?

2-5 years experience

1Your team added a new field 'region' and wants to change the shard key from 'category' to 'region' without downtime. How would you approach this migration, and what pitfalls would you watch for?
2After deploying a sharded cluster, you notice one shard is 80% full while others are barely used. What could cause this imbalance and how would you resolve it?
3A write operation to a sharded collection is failing with a 'StaleConfig' error. Walk me through how you'd debug and fix the issue.

5-8 years experience

1Design a sharding strategy for a high‑traffic IoT telemetry service that writes millions of documents per minute and queries by deviceId and timestamp. Explain your shard key choice, chunk size, and how you’d handle hot spots.
2Explain the trade‑offs between using a hashed shard key versus a ranged shard key for a social media feed service that needs chronological ordering.
3Your cluster experiences increased latency during a global read‑heavy campaign. How would you evaluate whether to add more shards, adjust balancer settings, or introduce read‑only secondary replicas?

8+ years experience

1Our company is moving from a monolithic MongoDB deployment to a globally distributed sharded architecture across three data centers. What architectural considerations, data migration plan, and operational safeguards would you put in place?
2Discuss how you would coordinate sharding changes (e.g., shard key redesign) across multiple product teams that each own different microservices, ensuring backward compatibility and minimal service disruption.
3Given a legacy system that cannot be sharded because of embedded transactions, propose a long‑term strategy to modernize the data layer while preserving existing business logic.

Follow-up Questions

Why did you pick that particular shard key?
What metrics would you monitor to detect shard imbalance?
How would you validate a shard‑key migration before rolling it out?

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