Tuning consistency vs performance in MongoDB - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the read concern level to 'majority' for stronger consistency.

MongoDB

db.collection.find().readConcern('[1]')

Drag options to blanks, or click blank then click option'

Amajority

Blinearizable

Cavailable

Dlocal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'local' which reads from the primary only and may not be fully consistent.

Using 'available' which is weaker consistency.

Setting readConcern to 'majority' ensures the query reads data acknowledged by a majority of nodes, improving consistency.

2fill in blank

medium

Complete the code to set the write concern to acknowledge writes by 3 nodes.

MongoDB

db.collection.insertOne(doc, { writeConcern: { w: [1] } })

Drag options to blanks, or click blank then click option'

A1

Bmajority

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using w: 1 which only waits for primary acknowledgment.

Using w: 0 which does not wait for any acknowledgment.

Setting writeConcern w to 3 means the write must be acknowledged by 3 nodes, increasing durability but possibly reducing performance.

3fill in blank

hard

Fix the error in the code to set read preference to nearest for better performance.

MongoDB

db.collection.find().readPreference('[1]')

Drag options to blanks, or click blank then click option'

AprimaryPreferred

Bprimary

CsecondaryPreferred

Dnearest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'primary' which always reads from the primary node, possibly slower.

Using 'secondaryPreferred' which prefers secondary but falls back to primary.

Using 'nearest' read preference allows reading from the closest node, improving read performance but possibly reducing consistency.

4fill in blank

hard

Fill both blanks to set a transaction with read concern 'snapshot' and write concern 'majority'.

MongoDB

session.startTransaction({ readConcern: { level: '[1]' }, writeConcern: { w: '[2]' } })

Drag options to blanks, or click blank then click option'

Asnapshot

Blocal

Cmajority

Dlinearizable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'local' read concern which is weaker for transactions.

Using write concern less than 'majority' which risks data loss.

Transactions use 'snapshot' read concern for consistent reads and 'majority' write concern for durability.

5fill in blank

hard

Fill both blanks to create a read operation with read preference 'secondary', read concern 'local'.

MongoDB

db.collection.find().readPreference('[1]').readConcern('[2]')

Drag options to blanks, or click blank then click option'

Aprimary

Bsecondary

Clocal

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'primary' read preference which reads only from primary.

Using read concern 'majority' which provides stronger consistency but may impact performance.

This configuration reads from secondary nodes with local consistency.