Tuning consistency vs performance in MongoDB - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Read Concern Levels

In MongoDB, which read concern level ensures that the data read is acknowledged by a majority of replica set members, balancing consistency and performance?

A majority

B local

C linearizable

D available

💡 Hint

Think about which level waits for most replicas to confirm the data.

The majority read concern ensures that the data read has been acknowledged by a majority of replica set members, providing a good balance between consistency and performance.

❓ query_result

intermediate

Effect of Write Concern on Acknowledgement

Given a MongoDB write operation with write concern set to { w: 1 }, what is the expected behavior regarding acknowledgement?

A The write is acknowledged only after all replica set members confirm it.

B The write is not acknowledged at all.

C The write is acknowledged after the primary node confirms it.

D The write is acknowledged after a majority of nodes confirm it.

💡 Hint

Consider what w:1 means in terms of acknowledgement.

Write concern { w: 1 } means the write is acknowledged after the primary node confirms it, which is faster but less durable than waiting for replicas.

📝 Syntax

advanced

Correct Syntax for Setting Read Concern in a Query

Which of the following MongoDB queries correctly sets the read concern to 'linearizable' for a find operation on the 'users' collection?

MongoDB

db.users.find({}, { readConcern: { level: 'linearizable' } })

A db.users.find().readConcern('linearizable')

B db.users.find({}, { readConcern: { level: 'linearizable' } })

C db.users.find().setReadConcern('linearizable')

D db.users.find({}, { readConcernLevel: 'linearizable' })

💡 Hint

Check the correct way to pass readConcern as an option in find.

The correct syntax is to pass readConcern as an option object in the second parameter of find(). Option B uses this correctly.

❓ optimization

advanced

Optimizing Write Performance with Write Concern

To maximize write performance in MongoDB while still ensuring the write is acknowledged by at least one node, which write concern setting should be used?

A { w: 0 }

B { w: 'all' }

C { w: 'majority' }

D { w: 1 }

💡 Hint

Consider the fastest acknowledged write concern.

Write concern { w: 1 } acknowledges the write after the primary node confirms it, maximizing performance while still providing acknowledgement.

🔧 Debug

expert

Diagnosing Read Consistency Issues

A MongoDB application reads data with read concern set to 'local' but sometimes gets stale data after a recent write. Which change will fix this issue by ensuring the read reflects the latest majority-committed data?

A Change read concern to 'majority'

B Change write concern to { w: 0 }

C Change read concern to 'available'

D Change write concern to { w: 1 }

💡 Hint

Think about which read concern guarantees reading majority-committed data.

Using readConcern: 'majority' ensures the read operation only returns data that has been committed by a majority of replica set members, preventing stale reads.