C100DBA Application Administration Practice Question
An application uses a MongoDB driver that supports retryable writes. A write operation is sent to the primary, which applies the write but crashes before sending the acknowledgment. The driver receives a network error. What will the driver do by default?
⚠ Common exam trap
The trap here is thinking that retryable writes retry indefinitely or not at all, when in fact they retry exactly once by default using a transaction number for deduplication.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Retry the write once, and the server will deduplicate it using the transaction number.
Retryable writes automatically retry a write operation once on retryable errors. The driver uses a transaction number and session ID so the server can deduplicate the retry, ensuring the write is applied exactly once. The driver does not retry indefinitely, does not skip retrying, and does not alter the write concern. The correct behavior is a single retry with deduplication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Retry the write indefinitely until it succeeds.
Why it's wrong here
Retryable writes retry only once by default. The driver does not retry indefinitely; it makes a single retry attempt. If the retry also fails with a retryable error, the driver returns the error to the application. Indefinite retries could cause delays and are not the default behavior. The application can implement its own retry logic if needed.
- ✗
Retry the write but with write concern 0 to avoid another failure.
Why it's wrong here
The driver does not change the write concern on retry. It retries with the same write concern and the same transaction number. Changing to write concern 0 would make the write unacknowledged and defeat the purpose of retryable writes, which is to ensure the write is applied exactly once. The driver maintains the original write concern for the retry.
- ✗
Return the error to the application without retrying.
Why it's wrong here
Retryable writes are enabled by default in modern drivers and will automatically retry on retryable errors. The driver does not simply return the error without retrying. It will attempt the retry once. Only if the retry fails will the error be propagated. So this option does not describe the default behavior.
- ✓
Retry the write once, and the server will deduplicate it using the transaction number.
Why this is correct
Retryable writes allow the driver to automatically retry a write operation once if it encounters a retryable error, such as a network error. The driver includes a transaction number and session ID, so the server can detect that the retry is the same operation and will not apply it twice. This ensures exactly-once semantics for the write. The driver will retry the write once by default.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
This C100DBA practice question is part of Courseiva's free MongoDB certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the C100DBA exam.