MongoDB MongoDB Sharding and Horizontal Scaling

Question 1

What are the three main components of a MongoDB sharded cluster?

Accepted Answer

Mongos, config servers, and shards

Answer

Primary, secondary, arbiter

Answer

Router, coordinator, and replica

Answer

Balancer, indexer, and data node

Question 2

What is a shard key in MongoDB sharding?

Accepted Answer

A field or combination of fields that determines how documents are distributed across shards

Answer

A unique index on every shard

Answer

An encryption key for shard-level data security

Answer

A password for shard authentication

Question 3

What is a monotonically increasing shard key and why is it problematic?

Accepted Answer

A shard key like a timestamp or auto-increment ID where all new inserts go to the same 'max' chunk, creating a hot spot

Answer

A shard key with random values that causes uneven distribution

Answer

A shard key that can only be used on a single shard

Answer

A shard key that changes over time causing documents to migrate

Question 4

What is the role of the balancer in a MongoDB sharded cluster?

Accepted Answer

Automatically moving chunks between shards to maintain even data distribution

Answer

Routing client queries to the correct shard

Answer

Managing replica set elections within each shard

Answer

Compressing data across shards

Question 5

What is a targeted (routed) query vs a scatter-gather query in a sharded cluster?

Accepted Answer

A targeted query includes the shard key and goes to one shard; a scatter-gather query broadcasts to all shards

Answer

A targeted query uses indexes; a scatter-gather query does not

Answer

A targeted query reads from secondaries; scatter-gather reads from primaries

Answer

A targeted query is synchronous; scatter-gather is asynchronous

Question 6

What is a hashed shard key in MongoDB and when should you use it?

Accepted Answer

A shard key where MongoDB hashes the field values to distribute documents evenly, ideal for monotonically increasing fields

Answer

A shard key encrypted for security purposes

Answer

A compound shard key using a hash of multiple fields

Answer

A shard key that uses SHA-256 for uniqueness guarantees