C100DBA Multiple Select — 10 Questions

Question 1

Which THREE of the following are core tenets of the MongoDB philosophy regarding data modeling?

Accepted Answer

Store data that is accessed together in the same document.. MongoDB's data modeling philosophy emphasizes placing data that is accessed together into the same document (embedding). It promotes flexibility by allowing schemas to be dynamic rather than rigid. Furthermore, it encourages developers to design schemas based on the application's specific query patterns, ensuring that the database layout directly supports the most frequent operations, which leads to optimal performance in high-scale environments where relational joins would otherwise create bottlenecks.

Answer

Normalize data to the third normal form.

Answer

Always prioritize write consistency over read performance.

Question 2

Which TWO of the following are essential for maintaining performance in a sharded cluster?

Accepted Answer

Selecting a shard key with high cardinality.. A well-chosen shard key is the most critical factor for even data distribution, while monitoring chunks ensures that data remains balanced across the cluster. If the shard key is poorly chosen, some shards may become bottlenecks (hotspots), while others remain underutilized. Proper chunk management prevents excessive migration and ensures that query routers (mongos) efficiently route requests to the appropriate shards, maintaining overall system stability and throughput.

Answer

Hardcoding the shard primary in the application connection string.

Answer

Disabling the balancer during all business hours.

Answer

Using the same shard key for every collection in the database.

Question 3

Which TWO of the following are benefits of the MongoDB 'document' model over the traditional 'relational' model?

Accepted Answer

Built-in support for complex, hierarchical data structures.. The document model excels in developer agility and data modeling flexibility. By grouping related data, it optimizes for common access patterns, which enhances read performance by reducing the need for joins. This approach aligns with modern programming paradigms where objects are the primary unit of development, allowing for faster iterations and easier maintenance compared to relational models that require complex schema changes and manual data normalization across multiple tables.

Answer

Requirement for strict normalization of all data.

Answer

Guaranteed consistency through mandatory schema migrations.

Answer

Automatic translation of SQL queries to BSON.

Question 4

Which THREE components are mandatory architectural parts of every fully functioning MongoDB sharded cluster deployment? Choose 3 answers.

Accepted Answer

A config server replica set that stores all cluster metadata, chunk ranges, and routing configuration data.. A sharded cluster relies on three core functional components: config servers to maintain cluster metadata, mongos query routers to direct client requests, and shard replicas to store partitioned data safely. Knowing these architecture requirements helps administrators design resilient, highly available production clusters with proper redundancy at every layer of the infrastructure.

Answer

A dedicated primary balancer coordinator node running outside the config server replica set to manage migrations.

Answer

An independent Apache ZooKeeper quorum cluster to coordinate distributed locking across all participating mongod nodes.

Question 5

Which THREE of the following are core pillars of the MongoDB architecture?

Accepted Answer

Horizontal scalability through sharding.. MongoDB's architecture is built on the principles of horizontal scalability, high availability, and developer-focused data modeling. These pillars allow MongoDB to handle massive scale and fluctuating workloads efficiently. By integrating sharding for capacity, replication for reliability, and flexible schemas for agility, the system addresses the common limitations of static relational databases, offering a comprehensive platform for modern, distributed cloud-native applications that require both speed and robustness in dynamic environments.

Answer

Strict, static schema enforcement at the storage layer.

Answer

Global dependency on a single centralized primary node.

Question 6

An administrator needs to create a restricted user for a third-party monitoring tool. The user must be able to perform backups and monitor server status but cannot read actual document data. Which TWO built-in roles should be combined?

Accepted Answer

backup. MongoDB's Role-Based Access Control (RBAC) allows for granular permission management. The 'backup' role provides the necessary privileges to use tools like mongodump without granting general read access to all collections. The 'clusterMonitor' role allows the user to run commands like 'serverStatus' and 'top', which are essential for monitoring performance.

Answer

readAnyDatabase

Answer

dbAdmin

Answer

hostManager

Question 7

A logistics company is designing a MongoDB database for a real-time shipment tracking system. The operations team needs to frequently update shipment statuses and query the latest events. The development team is debating the trade-offs of embedding versus referencing for the shipment events. Which two considerations align with MongoDB's philosophy for this scenario? (Choose two.)

Accepted Answer

Embedding events within the shipment document ensures atomic updates and fast reads for the event history.. The correct considerations are that embedding provides atomic updates and fast reads for the event history, while referencing allows unlimited growth and avoids the 16 MB limit. These reflect MongoDB's flexible modeling philosophy: choose embedding when data is accessed together and atomicity is needed, but opt for referencing when data grows unbounded or is accessed independently. The decision hinges on access patterns and data lifecycle.

Answer

Embedding events is always preferred because it eliminates the need for multi-document transactions.

Answer

Referencing events requires using $lookup for every read, which is as fast as an embedded document read.

Answer

Embedding events ensures that the shipment document remains small and efficient for writes.

Question 8

A DBA is reviewing update operations that use the upsert option. Which TWO statements about upsert behavior in MongoDB are correct? (Choose two.)

Accepted Answer

If no document matches the filter, upsert inserts a new document based on the filter and the update operators.. Upsert inserts a new document when the filter matches nothing, building it from equality conditions in the filter plus the update operators. Non-equality operators do not contribute fields, so the inserted document may lack the filtered field. A unique index is recommended to prevent duplicate inserts from concurrent upserts, but it is not mandatory. Array operators such as $push are allowed in upserts.

Answer

Upsert cannot be used with update operators that modify array elements, such as $push.

Answer

If multiple documents match the filter, upsert updates all of them and inserts no new document.

Answer

Upsert always requires a unique index on the filter fields to avoid duplicate inserts.

Question 9

A financial services company runs a sharded MongoDB cluster with three shards. They need to shard a new collection that stores transaction records. The collection will be queried primarily by 'accountId' and 'transactionDate'. The team wants to minimize scatter-gather queries and ensure even data distribution. Which two actions should they take when choosing and implementing the shard key? (Choose two.)

Accepted Answer

Ensure the shard key has high cardinality and low frequency to avoid jumbo chunks and hot spots.. The compound shard key with 'accountId' first supports targeted queries on account and range queries on date, while also providing high cardinality and low frequency. This combination reduces scatter-gather and avoids hot spots. Hashed or random keys improve distribution but break query targeting, and a monotonically increasing key creates write hot spots.

Answer

Choose a shard key that is monotonically increasing, such as an auto-incrementing transaction ID, to simplify range queries.

Answer

Use a random shard key generated by the application to guarantee even distribution across shards.

Answer

Use a hashed shard key on 'accountId' to ensure even distribution, even though it prevents efficient range queries on 'transactionDate'.

Question 10

A DBA is designing indexes for a collection that stores user activity logs. The collection has fields: user_id, action, timestamp, and metadata (an embedded document). The most common queries are: (1) find all actions for a given user_id sorted by timestamp descending; (2) find all users who performed a specific action within a time range. Which TWO indexes would best support these queries? (Choose two.)

Accepted Answer

{ user_id: 1, timestamp: -1 }. The two indexes that best support the queries are { user_id: 1, timestamp: -1 } for query (1) and { action: 1, timestamp: 1 } for query (2). The first provides an equality match on user_id and a sort on timestamp, while the second provides an equality match on action and a range on timestamp. These indexes align with the equality-sort and equality-range patterns, ensuring efficient index usage.

Answer

{ metadata: 1 }

Answer

{ user_id: 1, action: 1, timestamp: -1 }

Answer

{ timestamp: 1 }