Read preference for replica sets in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a read preference in MongoDB replica sets?

A read preference tells MongoDB which members of a replica set to read data from. It helps balance load and control data freshness.

beginner

Name the five standard read preference modes in MongoDB.

Primary, PrimaryPreferred, Secondary, SecondaryPreferred, and Nearest.

beginner

What does the 'Primary' read preference mode do?

It directs all read operations to the primary member of the replica set, ensuring the most up-to-date data but no load balancing.

intermediate

How does 'SecondaryPreferred' read preference work?

It reads from secondary members if available, but falls back to primary if no secondary is reachable, balancing freshness and availability.

intermediate

Why might you use the 'Nearest' read preference mode?

To read from the member with the lowest network latency, regardless of whether it is primary or secondary, improving read speed.

Which read preference mode always reads from the primary member?

A SecondaryPreferred

B Secondary

C Primary

D Nearest

The 'Primary' mode directs all reads to the primary member only.

If you want to read from a secondary but fall back to primary if no secondary is available, which mode do you choose?

A Primary

B PrimaryPreferred

C Nearest

D SecondaryPreferred

'SecondaryPreferred' reads from secondaries first, then primary if needed.

What does the 'Nearest' read preference mode prioritize?

A Member with lowest network latency

B Primary member only

C Secondary members only

D Random member

'Nearest' reads from the member with the lowest network latency.

Which read preference mode can help distribute read load across secondaries?

A Secondary

B PrimaryPreferred

C Primary

D Nearest

'Secondary' mode reads only from secondary members, helping distribute load.

What happens if you use 'PrimaryPreferred' and the primary is down?

A Reads fail immediately

B Reads go to secondaries

C Reads go to nearest member

D Reads go to arbiter

'PrimaryPreferred' reads from primary if available, else from secondaries.

Explain the purpose of read preferences in MongoDB replica sets and list the available modes.

Think about balancing data freshness and load distribution.

Describe a scenario where using 'SecondaryPreferred' read preference is beneficial.

Consider read load and data freshness trade-offs.