Write concern and data durability in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is write concern in MongoDB?

Write concern is a setting that tells MongoDB how sure it should be that a write operation has been saved before reporting success.

beginner

What does w: 1 mean in MongoDB write concern?

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

intermediate

How does w: 'majority' affect data durability?

It ensures the write is confirmed by the majority of replica set members, increasing data safety in case of failure.

intermediate

What is the role of j: true in write concern?

It requires the write to be committed to the journal on disk, improving durability by protecting against power loss.

advanced

Why might you choose a lower write concern like w: 0?

To improve performance by not waiting for any acknowledgment, but this risks losing data if the write fails.

What does write concern control in MongoDB?

A How many servers confirm a write before success

B The speed of the query execution

C The size of the database

D The number of indexes

Write concern controls how many servers must confirm a write operation before it is considered successful.

What does w: 'majority' ensure?

A Write is confirmed by the primary only

B Write is confirmed by most members in the replica set

C Write is confirmed by all members

D Write is not confirmed at all

w: 'majority' means the write must be acknowledged by most members of the replica set.

What does setting j: true do?

A Disables journaling

B Deletes journal files

C Speeds up writes by skipping disk

D Requires write to be saved to journal on disk

j: true ensures the write is saved to the journal on disk for durability.

Which write concern gives no acknowledgment of write success?

A w: 0

B w: 1

C w: majority

D j: true

w: 0 means no acknowledgment is required, so the client does not wait for confirmation.

Why is a higher write concern better for data durability?

A It deletes old data

B It makes writes faster

C It confirms writes on more servers, reducing data loss risk

D It compresses data

Higher write concern means more servers confirm the write, making data loss less likely.

Explain what write concern is and how it affects data durability in MongoDB.

Think about how many servers must say 'I saved it' before you trust the write.

Describe the difference between w: 1, w: majority, and w: 0 write concerns.

Consider how many confirmations each setting requires.