Capped collections for fixed-size data in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of inserting documents into a capped collection

Given a capped collection with a max size of 1000 bytes and max 3 documents, what will be the count of documents after inserting 4 documents?

MongoDB

db.createCollection('logs', { capped: true, size: 1000, max: 3 });
db.logs.insertMany([
  { event: 'start' },
  { event: 'process' },
  { event: 'end' },
  { event: 'cleanup' }
]);
db.logs.countDocuments();

A 4

B 3

C 2

D 1

💡 Hint

Remember capped collections keep only the most recent documents up to the max limit.

Capped collections automatically remove oldest documents when the max document count or size is exceeded. Here, max is 3, so after inserting 4 documents, only the latest 3 remain.

🧠 Conceptual

intermediate

Behavior of capped collections on document update

What happens when you update a document in a capped collection that increases its size beyond the allocated space?

A The update fails with an error because documents cannot grow in capped collections.

B The document is moved to a new location to accommodate the size increase.

C The document is truncated to fit the original size limit.

D The collection automatically increases its size to fit the updated document.

💡 Hint

Think about the fixed-size nature of capped collections.

In capped collections, documents cannot grow in size after insertion. Updates that increase document size will fail with an error.

📝 Syntax

advanced

Correct syntax to create a capped collection with size and max documents

Which of the following commands correctly creates a capped collection named 'events' with a max size of 5000 bytes and max 100 documents?

A db.createCollection('events', { capped: true, size: 5000, max: 100 });

B db.createCollection('events', { capped: true, maxSize: 5000, maxDocs: 100 });

C db.createCollection('events', { capped: true, size: 5000 }); db.events.setMaxDocuments(100);

D db.createCollection('events', { capped: true, size: '5000', max: '100' });

💡 Hint

Check the exact option names and data types for capped collection options.

The correct options are 'size' for bytes and 'max' for max documents. They must be numbers, not strings. There is no method setMaxDocuments.

❓ optimization

advanced

Optimizing capped collection size for high insert rate

You have a capped collection with size 1MB and max 1000 documents. Your application inserts 2000 documents per minute. What is the best way to avoid losing important recent data?

A Disable capping and use a normal collection with TTL indexes.

B Decrease the capped collection size to force faster removal of old data.

C Increase the capped collection size and max document count to hold more data.

D Insert documents in batches of 1000 to reduce overhead.

💡 Hint

Think about how capped collections manage storage and document retention.

Increasing size and max documents allows the capped collection to hold more data before removing old documents, preserving recent data better.

🔧 Debug

expert

Identifying error when inserting large document into capped collection

You created a capped collection with size 1024 bytes. When inserting a document of 1500 bytes, what error will MongoDB raise?

A No error, document is truncated automatically

B CappedPositionLost: document cannot fit in capped collection

C BSONObjectTooLarge: document exceeds maximum size

D WriteError: document size exceeds capped collection size

💡 Hint

Consider how capped collections handle documents larger than their size limit.

MongoDB raises a WriteError indicating the document size exceeds the capped collection size because capped collections cannot store documents larger than their allocated size.