DBS-C01 Workload-Specific Database Design Practice Test 7 — 15 Questions

Question 1

A company is designing a database for a real-time bidding system that requires sub-millisecond read and write latency for ad impressions. The workload is heavily write-intensive with occasional reads by campaign IDs. Which AWS database service is most suitable?

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

Accepted Answer

Amazon DynamoDB with DAX. Amazon DynamoDB with DAX is the most suitable choice because DynamoDB provides single-digit millisecond latency for read and write operations at any scale, and DAX (DynamoDB Accelerator) is an in-memory cache that reduces read latency to microseconds for frequently accessed items. This combination meets the sub-millisecond read and write latency requirements for a heavily write-intensive real-time bidding system, while supporting occasional reads by campaign IDs via efficient query patterns.

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Amazon ElastiCache for Redis

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Amazon DocumentDB

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Amazon Aurora MySQL

Question 2

A gaming company uses Amazon RDS for PostgreSQL to store player profiles and game state. They report slow queries during peak hours. The DB instance is a db.r5.2xlarge with 500 GB gp2 storage. Which design change would MOST improve read performance for the most frequently accessed player profiles?

Accepted Answer

Add a read replica in the same AZ. Adding a read replica in the same Availability Zone (AZ) offloads read traffic from the primary RDS for PostgreSQL instance, directly improving read performance for frequently accessed player profiles during peak hours. Read replicas asynchronously replicate data using PostgreSQL's streaming replication and can serve SELECT queries without impacting the primary instance's write workload or connection limits.

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Implement application-level sharding by player ID

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Increase provisioned IOPS on the existing volume

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Upgrade to a db.r5.4xlarge instance

Question 3

A financial services company needs a relational database with high availability and automatic failover across three Availability Zones in us-east-1. The workload consists of OLTP transactions with occasional analytic queries. Which database solution meets these requirements?

Accepted Answer

Amazon Aurora MySQL with Multi-AZ deployment across 3 AZs. Amazon Aurora MySQL with Multi-AZ deployment across 3 AZs meets the requirements because Aurora automatically replicates your data six ways across three Availability Zones, with a primary DB instance in one AZ and two read replicas in the other two AZs. In the event of a failure, Aurora automatically fails over to a read replica in under 30 seconds without data loss, providing high availability and automatic failover across three AZs. Aurora also supports both OLTP transactions and can handle occasional analytic queries via Aurora Replicas or Aurora Global Database for read scaling.

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Amazon RDS for MySQL with Multi-AZ (2 AZs)

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Amazon DynamoDB global tables

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Amazon Redshift with cross-region snapshots

Question 4

A company is migrating an on-premises MongoDB database to AWS. The database stores JSON documents for a content management system. The workload requires read-after-write consistency and automatic scaling. Which AWS database service is MOST appropriate?

Accepted Answer

Amazon DocumentDB. Amazon DocumentDB is the most appropriate choice because it is a fully managed, MongoDB-compatible document database that natively stores JSON documents, supports read-after-write consistency via its default session consistency model, and provides automatic scaling of storage (up to 64 TB) and compute resources. It directly replaces on-premises MongoDB workloads without requiring schema changes or application rewrites, making it ideal for a content management system.

Answer

Amazon ElastiCache for Redis

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Amazon DynamoDB

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Amazon RDS for PostgreSQL

Question 5

A company runs a global e-commerce platform with a relational database. They need to reduce read latency for users in Europe and Asia. The primary database is in us-west-2. Which solution provides the LOWEST read latency for global users while maintaining data consistency?

Accepted Answer

Use Amazon Aurora Global Database with reader instances in Europe and Asia. Amazon Aurora Global Database is designed for low-latency global reads by replicating data to up to five secondary regions with dedicated reader instances. It uses storage-based replication that typically adds less than one second of lag, ensuring strong consistency while providing local read access for users in Europe and Asia. This architecture directly addresses the requirement for the lowest read latency without compromising data consistency.

Answer

Deploy Amazon ElastiCache clusters in each region and cache database queries

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Migrate to Amazon DynamoDB global tables

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Configure Amazon RDS cross-region read replicas

Question 6

A startup is building a mobile application that requires a database to store user preferences and session data. The data is accessed by user ID and requires single-digit millisecond latency. The workload is read-heavy with occasional writes. Which database service is MOST cost-effective?

Accepted Answer

Amazon DynamoDB with on-demand capacity. Amazon DynamoDB with on-demand capacity is the most cost-effective choice because it provides single-digit millisecond latency for key-value lookups by user ID, scales automatically to handle read-heavy workloads with occasional writes, and charges only for the reads and writes consumed, avoiding the cost of provisioning for peak capacity. The on-demand mode eliminates the need for capacity planning, making it ideal for unpredictable or variable traffic patterns typical of a startup's mobile application.

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Amazon Aurora Serverless

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Amazon ElastiCache for Memcached

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Amazon RDS for MySQL with provisioned IOPS

Question 7

A company uses Amazon RDS for Oracle for an OLTP application. The database experiences high CPU utilization during peak hours. The application is read-heavy and can tolerate eventually consistent reads. Which solution reduces CPU load on the primary database with minimal application changes?

Accepted Answer

Create an RDS read replica and direct read traffic to it. Creating an RDS Read Replica offloads read traffic from the primary Oracle instance, directly reducing CPU utilization on the primary. Since the application is read-heavy and tolerates eventually consistent reads, the replica’s asynchronous replication lag is acceptable. This solution requires minimal application changes—only modifying the connection string to route SELECT queries to the replica endpoint.

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Implement Amazon ElastiCache to cache frequent queries

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Upgrade to a larger instance type

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Use DynamoDB Accelerator (DAX) as a cache layer

Question 8

A company is designing a database for an IoT application that ingests millions of sensor readings per second. Each reading includes device ID, timestamp, and measurement. The workload requires time-series analytics and data retention for 90 days. Which AWS database solution is MOST appropriate?

Accepted Answer

Amazon Timestream. Amazon Timestream is a purpose-built time-series database designed for IoT and operational applications that ingest millions of sensor readings per second. It automatically manages data retention policies (e.g., 90 days) by storing recent data in memory and historical data in a cost-optimized store, and it supports time-series analytics with built-in functions like interpolation and smoothing.

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Amazon Redshift with auto-copy from S3

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Amazon ElastiCache for Redis with time-series module

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Amazon DynamoDB with TTL

Question 9

A company needs a fully managed graph database for a social networking application that requires real-time recommendations based on friend connections. Which AWS service should they use?

Accepted Answer

Amazon Neptune. Amazon Neptune is the correct choice because it is a fully managed graph database service optimized for storing and querying highly connected data. It supports both property graph (Apache TinkerPop Gremlin) and RDF (SPARQL) models, making it ideal for social networking applications that require real-time friend-of-friend recommendations and traversal queries across complex relationships.

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Amazon DocumentDB

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Amazon ElastiCache

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Amazon DynamoDB

Question 10

A company is designing a disaster recovery strategy for an Amazon RDS for PostgreSQL database. They need a Recovery Point Objective (RPO) of less than 5 seconds and a Recovery Time Objective (RTO) of less than 1 minute. Which TWO actions should they take? (Choose two.)

Accepted Answer

Create a cross-region read replica and configure automatic failover using Amazon Route 53 health checks. A cross-region read replica can be promoted to a primary instance in under a minute, and with Amazon Route 53 health checks configured for automatic failover, the DNS update occurs automatically, meeting the RTO of less than 1 minute. The asynchronous replication lag is typically sub-second, achieving an RPO of less than 5 seconds. Option E is correct because a Multi-AZ deployment with a synchronous standby in another Availability Zone provides automatic failover with no data loss (RPO of 0) and failover completes in about 30-60 seconds, satisfying both RPO and RTO requirements.

Answer

Use AWS Database Migration Service for continuous replication to a separate instance

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Create a cross-region read replica and manually update DNS in a disaster

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Take hourly snapshots and restore in another region

Question 11

A company is migrating a large Oracle data warehouse to AWS. The warehouse contains 50 TB of data and runs complex analytical queries. The solution must support concurrency of up to 100 users and provide high performance for queries. Which THREE design decisions should the company make? (Choose three.)

Accepted Answer

Use distribution keys based on frequently joined columns. Distribution keys based on frequently joined columns ensure that related data is co-located on the same compute nodes, minimizing data movement across the network during joins. This is critical for complex analytical queries on large datasets in Amazon Redshift, as it reduces shuffle overhead and improves query performance.

Answer

Use Amazon RDS for Oracle with Multi-AZ

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Use Amazon DynamoDB with global tables

Question 12

A company is building a microservices architecture and needs a database for a service that stores JSON documents with variable schema. The database must support high availability and automatic scaling. Which TWO services meet these requirements? (Choose two.)

Accepted Answer

Amazon DynamoDB. Amazon DynamoDB is correct because it is a fully managed NoSQL key-value and document database that natively supports JSON documents with variable schema, offers high availability through multi-AZ replication, and provides automatic scaling via its on-demand capacity mode or auto-scaling policies. It is ideal for microservices architectures that require low-latency, serverless, and elastic throughput.

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Amazon ElastiCache for Redis

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Amazon Neptune

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Amazon RDS for MySQL

Question 13

Refer to the exhibit. An IAM policy is attached to an IAM role used by a Lambda function that writes to a DynamoDB table. The function also needs to read items from the table. What is the outcome of this policy?

Accepted Answer

The Lambda function can write items but cannot read items. The IAM policy includes an explicit Deny for the `dynamodb:GetItem` action on the table, which overrides any Allow statements due to the explicit deny evaluation logic in AWS IAM. Since the Lambda function assumes a role with this policy, it is denied read access while the Allow for `dynamodb:PutItem` permits write operations. Therefore, the function can write but cannot read items from the DynamoDB table.

Answer

The policy is invalid because it contains both Allow and Deny for the same table

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The Lambda function can both read and write items

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The Lambda function cannot perform any operations on the table

Question 14

Refer to the exhibit. A developer reports that the RDS MySQL instance 'mydb' is experiencing high write latency. The storage is gp2 with 100 GB. What is the MOST likely cause of the write latency?

Accepted Answer

The gp2 volume size is too small, resulting in insufficient baseline IOPS. The gp2 volume's baseline IOPS are determined by the volume size at a ratio of 3 IOPS per GB, up to 16,000 IOPS. With a 100 GB gp2 volume, the baseline IOPS is only 300 (100 × 3). This is insufficient for write-heavy workloads, causing write latency as the volume exhausts its IOPS credit balance and enters a throttled state. Burst credits can temporarily boost performance, but sustained high write throughput will deplete credits and lead to latency.

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There is a read replica causing replication lag

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The instance class db.r5.large does not provide enough memory

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Multi-AZ is not enabled, causing synchronous replication overhead

Question 15

Refer to the exhibit. A developer created a DynamoDB table 'UserSessions' with a simple primary key. The application needs to query by user_id as well. What design change should the developer make to support this query efficiently?

Accepted Answer

Create a Global Secondary Index on user_id. A Global Secondary Index (GSI) on user_id allows efficient querying by user_id without altering the base table's primary key structure. The base table uses a simple primary key (likely session_id), and a GSI provides a separate index with its own partition key (user_id) to support non-key attribute queries with eventual consistency, enabling the application to query by user_id efficiently without scanning the entire table.

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Use a Scan operation with a filter

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Add a sort key to the table

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Create a Local Secondary Index on user_id