Write concern basics in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is write concern in MongoDB?

Write concern is a setting that controls the level of acknowledgment requested from MongoDB when performing write operations. It tells MongoDB how sure you want to be that your data was saved.

beginner

What does w: 1 mean in write concern?

It means the write operation must be acknowledged by the primary server only before reporting success. This is the default level.

intermediate

What happens if you set w: 'majority' in write concern?

The write operation waits until a majority of replica set members have acknowledged the write. This increases data safety by ensuring replication.

intermediate

What is the role of wtimeout in write concern?

It sets a time limit (in milliseconds) for how long MongoDB waits for the write concern to be satisfied. If the time expires, an error is returned.

advanced

What does w: 0 mean and when might it be used?

It means no acknowledgment is requested from the server. The client does not wait for confirmation. It can be used for very fast writes where data loss is acceptable.

What does write concern control in MongoDB?

A The speed of queries

B The size of the database

C The number of indexes

D How many servers acknowledge a write operation

Write concern controls the level of acknowledgment from servers for write operations.

Which write concern value waits for acknowledgment from the primary only?

A w: 1

B w: all

C w: majority

D w: 0

w: 1 means acknowledgment from the primary server only.

What does setting wtimeout do?

A Defines the size of the write batch

B Sets the number of writes per second

C Limits how long to wait for write acknowledgment

D Specifies the number of indexes to update

wtimeout sets a time limit for waiting for write concern acknowledgment.

If you want the fastest write without waiting for confirmation, which write concern do you use?

A w: majority

B w: 0

C w: 1

D w: 2

w: 0 means no acknowledgment is requested, so writes are fastest but less safe.

What does w: 'majority' ensure?

A Write is acknowledged by a majority of replica set members

B Write is acknowledged by the primary only

C Write is acknowledged by all members

D Write is not acknowledged

w: 'majority' waits for acknowledgment from most replica set members.

Explain what write concern is and why it matters in MongoDB.

Think about how sure you want to be that your data is saved.

Describe the differences between write concern values w: 0, w: 1, and w: majority.

Consider how many servers confirm the write.