Oplog and replication mechanism in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to query the oplog collection in MongoDB.

MongoDB

db.local.oplog.rs.find([1])

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

A{ts: 1}

B{op: 'i'}

C{}

D{ns: 'test.collection'}

Attempts:

3 left

💡 Hint

Common Mistakes

Using a filter that restricts results unintentionally.

Leaving the parentheses empty without an object.

The oplog query requires a filter object. An empty filter {} returns all oplog entries.

2fill in blank

medium

Complete the code to find oplog entries for insert operations only.

MongoDB

db.local.oplog.rs.find({op: [1])

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

A'c'

B'u'

C'd'

D'i'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'u' or 'd' which filter updates or deletes instead of inserts.

Forgetting to put quotes around the operation code.

The op field in the oplog indicates the operation type. 'i' stands for insert.

3fill in blank

hard

Fix the error in the code to query oplog entries after a specific timestamp.

MongoDB

db.local.oplog.rs.find({ts: {$gt: [1])

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

ATimestamp(1, 0)

BISODate('2023-01-01')

Cnew Date()

DObjectId()

Attempts:

3 left

💡 Hint

Common Mistakes

Using ISODate or Date which do not match the oplog timestamp type.

Using ObjectId which is unrelated here.

The oplog ts field uses MongoDB Timestamp type, so the filter must use a Timestamp object.

4fill in blank

hard

Fill both blanks to create a query that finds oplog entries for updates on a specific namespace.

MongoDB

db.local.oplog.rs.find({op: [1], ns: [2])

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

A'u'

B'i'

C'test.collection'

D'admin.system'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i' instead of 'u' for updates.

Using wrong namespace strings.

The op value 'u' filters updates, and ns specifies the namespace like 'test.collection'.

5fill in blank

hard

Fill all three blanks to create a query that finds delete oplog entries on 'logs.events' namespace after a given timestamp.

MongoDB

db.local.oplog.rs.find({op: [1], ns: [2], ts: {$gt: [3])

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

A'd'

B'logs.events'

CTimestamp(1672531200, 1)

D'admin.system'

Attempts:

3 left

💡 Hint

Common Mistakes

Using string dates instead of Timestamp.

Mixing up operation codes.

Incorrect namespace format.

Use 'd' for delete operations, specify the namespace as 'logs.events', and use a Timestamp object for the timestamp filter.