Be able to read a connection string and choose readPreference, readConcern, writeConcern, and pool sizes that match the application's consistency and load needs. The single most important thing: pick the weakest concern that still satisfies the requirement, and keep documents from growing on update.
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Domain overview
Application Administration on C100DBA covers how client applications connect to and behave against MongoDB deployments: connection string options, read and write concern, connection pool sizing, and schema patterns that keep documents and indexes healthy under heavy update load. Questions are scenario-based, asking you to pick the option that best preserves consistency, performance, and stability.
Exam objectives
Read preference and readConcern settings in the MongoDB connection string for consistent reads
Connection pool sizing via maxPoolSize and minPoolSize in the driver URI
Write concern and update operators that limit document growth and fragmentation
Sharded cluster components: mongos routers, config servers, and shard key choice
Choosing readConcern majority or linearizable everywhere, ignoring the latency cost when the application only needs local reads.
Setting maxPoolSize far above what the server can handle, causing connection storms instead of reusing pooled connections.
Assuming updates never move documents, when growing documents can force relocation and fragment data files.
Click any question to see the full explanation and answer options, or start a focused practice session above.
An application needs to update a user's balance. Which method ensures the operation is atomic for a single document?
2Refer to the exhibit. An aggregation pipeline is failing with an error. How can you modify the pipeline to allow it to process the large dataset?
3Which connection string parameter should be used to ensure that an application only reads data from nodes that are considered current and consistent?
4An application uses a time-series collection. What is the benefit of using the TTL (Time-To-Live) index feature?
5Which TWO of the following are essential for maintaining performance in a sharded cluster?
6What is the purpose of the 'write concern' in MongoDB?
7An application is performing many updates to a document. Which strategy is most effective to avoid fragmentation in the data files?
8Which connection string parameter should be used to ensure an application driver automatically discovers all members of a replica set?
9Refer to the exhibit. What is the primary cause of the performance issue seen in this query plan?
10Which read preference allows the application to read from the closest member of the replica set to minimize network latency?
11An application is using a capped collection for logging. What happens when the collection reaches its configured size limit?
12Which mechanism ensures an application receives an error if a write is not persisted to the majority of nodes in a replica set?
13When designing an application, what is the best practice for handling connection pools?
14Which MongoDB feature allows an application to receive real-time updates when data changes in a collection?
15An application uses a compound index on `{ 'status': 1, 'priority': -1 }`. Which query will efficiently use this index?
16What is the primary function of the 'wtimeout' setting in write concern?
17Which read concern provides the strongest consistency guarantee by ensuring the data returned has been acknowledged by a majority of the replica set?
18An application needs to perform a series of reads and writes across multiple documents in two collections atomically. The deployment is a replica set running MongoDB 4.2. Which feature should the application use?
19A development team is building a Node.js application that connects to a MongoDB replica set. They want the driver to automatically retry certain write operations once if they fail due to a transient network error, without requiring custom retry logic in their code. Which connection string option should they enable?
20A financial application must ensure that once a transaction is committed, the data will never be rolled back, even if the primary node crashes immediately after the write is acknowledged. Which write concern should be used?
21A MongoDB DBA is configuring a new application to connect to a sharded cluster. The application requires that reads are distributed across shards and that the driver automatically routes queries to the appropriate shard based on the shard key. Which component must be included in the connection string to enable this routing?
22An 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?
23A MongoDB application requires that reads never see data that could be rolled back, even in the event of a replica set failover. The application also needs to read from secondary nodes to distribute load. Which read concern should be used with a secondary read preference?
24A financial application requires that read operations never return data that could later be rolled back, even if it means reading from a secondary. The application connects to a replica set with readPreference=secondary. Which read concern level should be used to guarantee that the data read has been acknowledged by a majority of replica set members and cannot be rolled back?
25A developer is using the MongoDB Node.js driver and wants to ensure that a write operation is acknowledged by a majority of replica set members and is also written to the on-disk journal before returning success. Which write concern should be specified?
26A database administrator wants to configure a read preference that directs all read operations to the primary node of a replica set, ensuring the most up-to-date data. Which read preference mode should be used?
27A database administrator is configuring a MongoDB replica set. The application requires that writes are acknowledged by a majority of voting members before being considered successful, and that the write is also written to the on-disk journal before acknowledgment. Which write concern specification achieves this?
Be able to read a connection string and choose readPreference, readConcern, writeConcern, and pool sizes that match the application's consistency and load needs. The single most important thing: pick the weakest concern that still satisfies the requirement, and keep documents from growing on update.
The Courseiva C100DBA question bank contains 27 questions in the Application Administration domain. Click any question to see the full explanation and answer breakdown.
Start with a 10-question focused session to identify your baseline accuracy in this domain. Read every explanation — even for questions you answer correctly — to understand the reasoning. Once you score consistently above 80%, move to a 20–30 question session to confirm depth before moving to the next domain.
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