Read preference for replica sets in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the read preference to primary in a MongoDB client connection.

MongoDB

const client = new MongoClient(uri, { readPreference: '[1]' });

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

AprimaryPreferred

Bsecondary

Cprimary

Dnearest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'secondary' when you want to read from primary.

Confusing 'primaryPreferred' with 'primary'.

The primary read preference directs all reads to the primary member of the replica set.

2fill in blank

medium

Complete the code to set the read preference to read from secondary members only.

MongoDB

const client = new MongoClient(uri, { readPreference: '[1]' });

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

Asecondary

Bprimary

CprimaryPreferred

Dnearest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'primary' or 'primaryPreferred' instead of 'secondary'.

Confusing 'nearest' with 'secondary'.

The secondary read preference directs reads only to secondary members of the replica set.

3fill in blank

hard

Fix the error in the code to set the read preference to 'nearest'.

MongoDB

const client = new MongoClient(uri, { readPreference: [1] });

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

A'nearest'

Bnearest

C"nearest"

D'secondary'

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the string value causes a syntax error.

Using the wrong read preference string.

The readPreference value must be a string, so it needs quotes around it.

4fill in blank

hard

Fill both blanks to create a MongoDB client that reads from secondary members but falls back to primary if no secondary is available.

MongoDB

const client = new MongoClient(uri, { readPreference: '[1]', readPreferenceTags: [ { '[2]': '' } ] });

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

AsecondaryPreferred

Bsecondary

Cprimary

Ddc

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'secondary' instead of 'secondaryPreferred' causes no fallback.

Using incorrect tag keys in readPreferenceTags.

secondaryPreferred reads from secondaries but falls back to primary if none are available. The dc tag is commonly used to specify a data center for read preference tags.

5fill in blank

hard

Fill all three blanks to create a MongoDB client that reads from the nearest member in the 'east' data center with a max staleness of 120 seconds.

MongoDB

const client = new MongoClient(uri, { readPreference: '[1]', readPreferenceTags: [ { '[2]': '[3]' } ], maxStalenessSeconds: 120 });

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

Anearest

Bdc

Ceast

Dsecondary

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'secondary' instead of 'nearest' changes read behavior.

Incorrect tag keys or values cause no filtering.

nearest reads from the closest member regardless of primary or secondary. The dc tag filters members in the 'east' data center. maxStalenessSeconds limits how stale the data can be.