Ordered vs unordered inserts in MongoDB - Practice Questions

Challenge - 5 Problems

❓ query_result

intermediate

What happens with ordered inserts on duplicate key error?

Consider a MongoDB collection with a unique index on the field username. You run an ordered insert of three documents:

[{username: 'alice'}, {username: 'bob'}, {username: 'alice'}]

What will be the result of this insert operation?

MongoDB

db.users.insertMany([{username: 'alice'}, {username: 'bob'}, {username: 'alice'}], {ordered: true})

A All three documents are inserted despite the duplicate key error.

B The insert stops at the duplicate 'alice' and only the first two documents are inserted.

C None of the documents are inserted because of the duplicate key error.

D Only the first document is inserted; the rest are ignored.

💡 Hint

Ordered inserts stop at the first error and do not continue inserting remaining documents.

With ordered inserts, MongoDB inserts documents in order and stops at the first error, so the duplicate key error on the third document stops the process. The first two documents are inserted.

❓ query_result

intermediate

What is the behavior of unordered inserts on duplicate key error?

Using the same collection with a unique index on username, you run an unordered insert of three documents:

[{username: 'alice'}, {username: 'bob'}, {username: 'alice'}]

What will be the result of this insert operation?

MongoDB

db.users.insertMany([{username: 'alice'}, {username: 'bob'}, {username: 'alice'}], {ordered: false})

A The first two unique documents are inserted; the duplicate causes an error but does not stop the insert.

B The insert stops at the first error and no documents are inserted.

C None of the documents are inserted because of the duplicate key error.

D Only the first document is inserted; the rest are ignored due to errors.

💡 Hint

Unordered inserts try to insert all documents even if some cause errors.

With unordered inserts, MongoDB attempts to insert all documents regardless of errors. The duplicate key error on the third document causes an error, but the first two unique documents are inserted.

🧠 Conceptual

advanced

Why choose unordered inserts over ordered inserts?

Which of the following is the best reason to use unordered inserts in MongoDB?

A To maximize insert speed by allowing parallel insertion and continuing despite errors.

B To guarantee that no duplicate key errors occur during insertion.

C To ensure documents are inserted in a specific order without interruption.

D To automatically rollback all inserts if any error occurs.

💡 Hint

Think about performance and error handling when inserting many documents.

Unordered inserts allow MongoDB to insert documents in parallel and continue inserting even if some documents cause errors, improving speed and throughput.

🔧 Debug

advanced

Identify the error in this unordered insert usage

A developer tries to insert documents unordered but writes:

db.collection.insertMany(docs, {order: false})

What error or behavior will this cause?

A The insertMany operation will ignore the option and perform ordered inserts.

B The operation will throw a runtime error about invalid option.

C The insertMany operation will run unordered as intended.

D A syntax error will occur because the option key is incorrect.

💡 Hint

Check the exact option name for controlling order in insertMany.

The correct option key is 'ordered', not 'order'. Using 'order' is ignored or causes an error depending on driver version.

❓ optimization

expert

Optimizing bulk inserts with mixed valid and duplicate documents

You have 1000 documents to insert into a MongoDB collection with a unique index. Some documents have duplicate keys. You want to insert as many valid documents as possible quickly and get a report of errors.

Which approach is best?

A Use ordered inserts to stop at first error and fix duplicates before retrying.

B Insert documents one by one and catch errors individually.

C Use unordered inserts to insert all valid documents in parallel and collect errors after.

D Disable the unique index temporarily, insert all documents, then re-enable the index.

💡 Hint

Consider speed and error handling for large bulk inserts with duplicates.

Unordered inserts allow MongoDB to insert all valid documents quickly without stopping at errors. Errors are reported after, enabling efficient bulk insertion.