C100DEV Drivers, Tools, Transactions, and Search Practice Test 4 — 15 Questions

Question 1

A developer is using the MongoDB Node.js driver to perform a multi-document transaction that includes a read operation on a collection with a read concern of 'snapshot'. What is the effect of using 'snapshot' read concern in this transaction?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

It provides a consistent snapshot of the data at the start of the transaction, ensuring reads see the same version of documents throughout the transaction.. In a multi-document transaction, using snapshot read concern guarantees that all reads within the transaction see a consistent snapshot of the data as of the transaction start. This prevents anomalies such as non-repeatable reads and ensures that the transaction operates on a stable view of the data, which is critical for maintaining integrity.

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It allows reads to see uncommitted changes from other transactions, improving performance.

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It ensures that reads are distributed across secondary nodes for load balancing.

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It automatically retries reads if a transient error occurs, without failing the transaction.

Question 2

A developer is using mongosh to connect to a MongoDB Atlas cluster and needs to run several administrative commands. The developer wants to ensure that the connection uses the correct authentication database and that all commands are executed with the appropriate read preference. Which mongosh command-line option should be used to specify the authentication database?

Accepted Answer

--authenticationDatabase. In mongosh, the --authenticationDatabase option explicitly sets the database used for authentication. This is necessary when user credentials reside in a database other than the default (often admin). Other options like --db or --readPreference affect connection behavior but not authentication. Specifying the correct authentication database ensures that the provided username and password are validated against the intended database.

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--readPreference

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--username

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--db

Question 3

A developer is debugging a multi-document transaction in the MongoDB Node.js driver. The transaction updates a document in the `orders` collection and inserts into `audit`. The commit fails with a `WriteConflict` error that does not carry the `TransientTransactionError` label. What is the most appropriate action?

Accepted Answer

Inspect the error, resolve the conflict by re-reading or reordering operations, and retry the transaction with backoff.. A WriteConflict that lacks the TransientTransactionError label is not automatically retryable by the driver's standard loop. The developer must inspect the error and decide how to resolve the conflict, often by re-reading the latest document version or reordering operations, then retrying with backoff. Blindly retrying the commit or the whole transaction without addressing the cause is unlikely to succeed.

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Retry the entire transaction from the beginning.

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Retry only the commit operation with the same transaction number.

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Abort the transaction and report a permanent failure to the user.

Question 4

A developer wants to run ad-hoc queries against a MongoDB Atlas cluster from a terminal, including commands like db.collection.find() and db.adminCommand({listDatabases: 1}). The developer has the connection string and wants the least additional setup. Which tool should be used?

Accepted Answer

mongosh with the connection string passed as an argument. mongosh is the official MongoDB Shell and is designed for interactive, terminal-based querying and administration. It connects directly with a connection string and supports both CRUD helpers and database commands, so it covers the developer's needs with minimal setup. GUI tools, backup utilities, and federation features serve different purposes and would require more configuration or would not run in a terminal.

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MongoDB Compass connected to the cluster

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Atlas Data Federation with an S3 data source

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mongodump with the --uri option

Question 5

A developer needs to create an Atlas Search index that supports autocomplete on a `name` field. Which Atlas Search index definition is required?

Accepted Answer

An index with a field of type 'autocomplete' and an analyzer such as 'lucene.standard' or a custom edge-gram analyzer.. Atlas Search uses the `autocomplete` field type to support prefix suggestions. The field must be configured with an analyzer that produces edge-grams or n-grams, such as a custom analyzer using the edgeGram tokenizer. Standard string or text indexes do not provide this behavior. Wildcard indexes are unrelated to Atlas Search and cannot satisfy the autocomplete requirement.

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A text index with the default language analyzer.

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A standard string index with dynamic mapping enabled.

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A wildcard index on the `name` field.

Question 6

A developer is building a Node.js application that connects to a MongoDB replica set. The application must ensure that every read operation sees a consistent snapshot of the data, even if other clients are concurrently modifying documents. Which read concern level should be used for these reads?

Accepted Answer

"snapshot". The "snapshot" read concern provides a consistent snapshot of the data across multiple documents, ensuring that the application sees a stable view even with concurrent writes. Other read concerns like "local", "majority", or "available" do not offer this snapshot isolation, so they are unsuitable for the stated requirement.

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"local"

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"available"

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"majority"

Question 7

A developer is configuring an Atlas Search index on a collection of product documents. The index definition uses a dynamic mapping. Which two statements accurately describe the behavior or configuration of Atlas Search indexes in this scenario? (Choose two.)

Accepted Answer

Atlas Search indexes are stored in a separate search process and are updated asynchronously from the primary replica set.. Dynamic mapping in Atlas Search automatically indexes supported field types without per-field declarations, and the search index itself is maintained by a separate process that receives changes asynchronously from the replica set. The other statements misstate requirements or availability: analyzers are not mandatory for every string under dynamic mapping, Atlas Search is unavailable outside Atlas, and underscore-prefixed fields like _id are not dynamically indexed.

Answer

Dynamic mappings index fields whose names begin with an underscore, such as _id, by default.

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Atlas Search indexes can be created on any MongoDB deployment, including self-managed community servers.

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Setting dynamic to true requires also specifying analyzers for every string field in the collection.

Question 8

A developer needs to perform a point-in-time backup of a MongoDB replica set while the database remains online and serving reads and writes. Which MongoDB Database Tool is designed for this task?

Accepted Answer

mongodump with --oplog. mongodump with --oplog is the MongoDB Database Tool that captures both data and oplog entries during a live dump, enabling point-in-time restore. It runs against a running replica set without downtime. mongoexport lacks oplog capture, mongorestore applies dumps rather than creating them, and mongostat is a monitoring tool, so none of those meet the backup requirement.

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mongostat with --discover

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mongorestore with --archive

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mongoexport with --query

Question 9

A developer needs to quickly inspect the contents of a collection and run ad-hoc queries against a MongoDB Atlas cluster without installing any additional software. Which tool should be used?

Accepted Answer

Atlas Data Explorer. Atlas Data Explorer is a web-based interface integrated into MongoDB Atlas that lets users view and query data without installing any software. It is the most convenient tool for quick inspection and ad-hoc queries, as it is accessible directly from the Atlas UI and requires no local setup.

Answer

MongoDB Database Tools

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MongoDB Compass

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mongosh

Question 10

A developer needs to load a large JSON file into a collection named 'inventory' in the 'retail' database on a MongoDB server running on localhost. The file contains one JSON document per line. Which command-line tool should be used?

Accepted Answer

mongoimport --db retail --collection inventory --file inventory.json. The correct tool is mongoimport, which is part of the MongoDB Database Tools and specifically built to import data from JSON, CSV, or TSV files into a collection. The other tools serve different purposes: mongorestore restores BSON dumps, mongoexport exports data, and mongofiles manages GridFS files. Only mongoimport matches the requirement of loading a JSON file into a collection.

Answer

mongofiles --db retail --collection inventory --file inventory.json

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mongoexport --db retail --collection inventory --file inventory.json

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mongorestore --db retail --collection inventory inventory.json

Question 11

A developer is using the MongoDB Node.js driver to perform a multi-document transaction that includes a read operation on a collection with a read concern of 'snapshot'. What is the effect of using 'snapshot' read concern in this transaction?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Call session.abortTransaction() to roll back the update, then retry the entire transaction if appropriate.. In a multi-document transaction, if any operation fails, the entire transaction must be aborted to maintain atomicity. The correct action is to call abortTransaction() to roll back all changes made within the transaction. Committing or ignoring the error would lead to inconsistent data. Ending the session does not explicitly abort. Retrying without aborting is futile.

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Retry the insert operation within the same transaction without aborting, hoping the duplicate key error resolves.

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Call session.commitTransaction() to commit the successful update and ignore the failed insert.

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Call session.endSession() to close the session and automatically roll back the transaction.

Question 12

A developer is building an application that uses the MongoDB Node.js driver to perform a multi-document transaction. The transaction includes an update to an 'inventory' collection and an insert into an 'orders' collection. During testing, the developer notices that occasionally the transaction aborts with a TransientTransactionError. What is the most appropriate way to handle this error in the application code?

Accepted Answer

Immediately retry the entire transaction from the beginning.. TransientTransactionError is a label indicating a temporary failure that may be resolved by retrying the transaction. The correct approach is to retry the entire transaction, often using the driver's built-in retry mechanism like withTransaction. Aborting without retry, committing despite the error, or restarting the server are all inappropriate responses that could lead to data inconsistency or unnecessary failures.

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Restart the MongoDB server to clear the error condition.

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Commit the transaction and ignore the error, as the changes may have been applied.

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Abort the transaction and return an error to the user without retrying.

Question 13

A developer needs to import a large JSON file into a MongoDB collection named 'products' in the 'catalog' database. The file contains one JSON document per line (JSON Lines format). Which MongoDB tool should be used to accomplish this efficiently?

Accepted Answer

mongoimport. The task requires importing a JSON Lines file into a MongoDB collection. mongoimport is the designated tool for importing JSON, CSV, or TSV data. It handles JSON Lines natively and is optimized for bulk imports. The other tools serve different purposes: mongorestore is for BSON backups, mongodump is for creating backups, and mongostat is for monitoring.

Answer

mongorestore

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mongodump

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mongostat

Question 14

A developer needs to quickly inspect the contents of a MongoDB collection and run ad-hoc queries during development. The developer prefers a command-line interface that supports JavaScript syntax and allows direct interaction with the database. Which MongoDB tool should be used?

Accepted Answer

mongosh. mongosh is the official command-line shell for MongoDB, supporting JavaScript syntax and enabling direct interaction with the database for ad-hoc queries and administration. It is the appropriate tool for a developer who prefers a command-line interface. The other options are either GUI-based, cloud services, or specialized utilities not intended for interactive querying.

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MongoDB Compass

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MongoDB Database Tools

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MongoDB Atlas

Question 15

A developer is using the MongoDB Node.js driver to perform a multi-document transaction that includes a read operation on a collection with a read concern of 'snapshot'. What is the effect of using 'snapshot' read concern in this transaction?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

snapshot. Within a multi-document transaction, the read concern must be 'snapshot' to ensure a consistent snapshot of the data for all operations in the transaction. This provides the required isolation and atomicity. Other read concerns like 'local', 'majority', or 'linearizable' do not provide the same guarantees within a transaction and may not be supported.

Answer

linearizable

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local

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majority