Read preference for replica sets in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Which read preference returns data only from the primary?

In MongoDB replica sets, which read preference ensures that all read operations return data only from the primary node?

A secondary

B secondaryPreferred

C primary

D nearest

💡 Hint

Think about which node is the main source of truth in a replica set.

The 'primary' read preference directs all reads to the primary node, which is the main writable node in a replica set.

❓ query_result

intermediate

What is the output of this read preference setting?

Given the MongoDB read preference set to 'secondaryPreferred', where will the read operations be directed if a secondary is available?

A Reads go to a secondary node if available, otherwise to the primary.

B Reads go only to the nearest node regardless of type.

C Reads go only to the primary node.

D Reads go only to secondary nodes and never to primary.

💡 Hint

Consider the fallback behavior of 'secondaryPreferred'.

'secondaryPreferred' tries to read from a secondary but falls back to primary if no secondary is available.

🧠 Conceptual

advanced

Which read preference minimizes read latency by choosing the closest node?

In a MongoDB replica set, which read preference directs read operations to the node with the lowest network latency, regardless of whether it is primary or secondary?

A nearest

B primary

C primaryPreferred

D secondary

💡 Hint

Think about the read preference that considers network distance.

The 'nearest' read preference sends reads to the node with the lowest network latency, whether primary or secondary.

📝 Syntax

advanced

Identify the correct syntax to set read preference to 'secondary' in a MongoDB connection string

Which of the following MongoDB connection strings correctly sets the read preference to 'secondary'?

A mongodb://host1,host2/?read_preference=secondary

B mongodb://host1,host2/?readPreference=secondary

C mongodb://host1,host2/?readPreference=Secondary

D mongodb://host1,host2/?readPreferenceSecondary

💡 Hint

Check the exact parameter name and case sensitivity.

The correct parameter is 'readPreference' with exact casing and the value 'secondary' in lowercase.

❓ optimization

expert

Optimizing read preference for a geographically distributed replica set

You have a MongoDB replica set with nodes in three different continents. You want to minimize read latency for users worldwide while ensuring strong consistency when necessary. Which read preference strategy should you use?

A Use 'secondary' only to avoid primary node load, ignoring consistency.

B Use 'secondaryPreferred' for all operations to balance load evenly.

C Always use 'primary' to ensure strong consistency, ignoring latency.

D Use 'nearest' for reads to minimize latency, and 'primary' for writes to ensure consistency.

💡 Hint

Consider balancing latency and consistency requirements.

Using 'nearest' for reads reduces latency by reading from the closest node, while writes go to the primary to maintain strong consistency.