DBS-C01 Workload-Specific Database Design Practice Test 8 — 15 Questions

Question 1

A company is deploying a globally distributed application with users in the US, Europe, and Asia. The application requires sub-10ms read latency for user profiles stored in Amazon DynamoDB. Writes are less frequent. Which configuration meets the latency requirement while minimizing write conflicts?

Accepted Answer

Use DynamoDB global tables to replicate data to Regions close to users.. DynamoDB global tables provide multi-region, multi-active replication with eventual consistency, enabling sub-10ms reads from local replicas while writes are replicated asynchronously. This minimizes write conflicts because DynamoDB uses last-writer-wins (LWW) conflict resolution, which is acceptable for user profiles where writes are infrequent and conflicts are rare.

Answer

Deploy Amazon RDS for MySQL with Multi-AZ and cross-Region read replicas.

Answer

Use Amazon ElastiCache for Redis Global Datastore with DynamoDB as backing store.

Answer

Deploy a single DynamoDB table in us-east-1 with DAX caches in each region.

Question 2

A company is migrating a 5 TB Microsoft SQL Server database to Amazon RDS for SQL Server. The database has many stored procedures and triggers. The migration must have minimal downtime. Which approach should be used?

Accepted Answer

Use AWS DMS with full load and ongoing replication (CDC).. Option C is correct because AWS DMS with full load and ongoing change data capture (CDC) enables continuous replication of changes from the source SQL Server to the target Amazon RDS for SQL Server, minimizing downtime to a brief cutover window. This approach handles the migration of stored procedures and triggers as part of the schema conversion via AWS SCT, while CDC captures ongoing transactions to keep the target synchronized until the final switch.

Answer

Use AWS SCT to convert the database schema and then use DMS for data load.

Answer

Use the SQL Server Import/Export wizard to copy data.

Answer

Take a native backup, copy to Amazon S3, and restore to RDS during a maintenance window.

Question 3

A startup is building a mobile app that requires a scalable NoSQL database. The data model includes user profiles with variable attributes that change over time. The database must support high read throughput and low latency. Which AWS database is best suited?

Accepted Answer

Amazon DynamoDB. Amazon DynamoDB is a fully managed NoSQL key-value and document database that delivers single-digit millisecond latency at any scale. It supports flexible schema with variable attributes, making it ideal for user profiles that change over time, and its provisioned or on-demand capacity modes enable high read throughput with consistent low latency.

Answer

Amazon Neptune

Answer

Amazon RDS for MySQL

Answer

Amazon Redshift

Question 4

A company uses Amazon RDS for MySQL with a Multi-AZ deployment. During a recent failover, the application experienced a 2-minute downtime because it was connecting to the primary instance endpoint. The company needs to reduce failover downtime to under 30 seconds. What should be done?

Accepted Answer

Use the Multi-AZ DB cluster endpoint instead of the instance endpoint.. The Multi-AZ DB cluster endpoint provides a single DNS name that automatically routes connections to the current writer instance, eliminating the need for application-side reconnection logic. During a failover, the endpoint updates its DNS record to point to the new primary within seconds, reducing downtime to under 30 seconds. This is the recommended approach for minimizing failover disruption in Multi-AZ deployments.

Answer

Implement Amazon ElastiCache to cache database connections.

Answer

Increase the instance size to improve failover speed.

Answer

Deploy a read replica and promote it manually during failover.

Question 5

Which TWO factors should be considered when choosing between Amazon DynamoDB and Amazon RDS for MySQL for a new e-commerce application with variable traffic patterns?

Accepted Answer

Operational overhead: DynamoDB is serverless, RDS requires patching and provisioning.. Option B is correct because DynamoDB is a fully managed serverless service that eliminates the need for patching, provisioning, or managing servers, whereas Amazon RDS for MySQL requires manual patching, scaling, and instance provisioning. This operational overhead difference is critical for variable traffic patterns, as DynamoDB automatically handles infrastructure management, reducing administrative burden.

Answer

Ability to perform complex joins and aggregations: DynamoDB supports SQL-like queries.

Answer

Support for ACID transactions in both databases.

Answer

Encryption at rest is only available for RDS.

Question 6

Which THREE design patterns can improve the performance of a write-heavy application using Amazon DynamoDB?

Accepted Answer

Write sharding by using a composite key with a random suffix to distribute writes across partitions.. Option A is correct because write sharding with a random suffix on the partition key distributes writes evenly across multiple partitions, preventing hot partitions. This pattern avoids throttling by ensuring no single partition exceeds its write capacity limit, which is critical for write-heavy workloads in DynamoDB.

Answer

Create local secondary indexes (LSIs) for all query patterns.

Answer

Increase provisioned write capacity units (WCUs) to the maximum allowed.

Question 7

Which TWO Amazon RDS features can be used to increase the availability of a production database?

Accepted Answer

Cross-Region read replicas with automatic promotion.. Option B is correct because cross-Region read replicas provide a secondary copy of the database in a different AWS Region, which can be manually promoted to a standalone primary instance in the event of a regional outage. This feature increases availability by enabling a disaster recovery strategy that goes beyond a single AWS Region, ensuring business continuity even if the entire primary Region becomes unavailable.

Answer

Enhanced Monitoring and Performance Insights.

Answer

Manual DB snapshot taken every hour.

Answer

Automated backups with a retention period of 35 days.

Question 8

An IAM policy is attached to a user to allow read access to the Orders table in DynamoDB. The user reports that a GetItem call for an order returns an 'AccessDeniedException'. What is the likely cause?

Accepted Answer

The user must specify a projection expression in the GetItem request to include only 'order_id' and 'status' attributes.. Option A is correct because when an IAM policy uses the `dynamodb:Attributes` condition key to restrict access to specific attributes (e.g., `order_id` and `status`), the user must include a `ProjectionExpression` in the `GetItem` request that explicitly lists only those allowed attributes. Without the projection expression, DynamoDB attempts to return all attributes, which triggers an `AccessDeniedException` because the policy denies access to attributes not listed in the condition.

Answer

The user does not have permissions to perform GetItem on the Orders table.

Answer

The resource ARN is incorrect; it should include the wildcard for the table.

Answer

The condition key 'dynamodb:Attributes' restricts access to only two attributes, but the user can still get all attributes.

Question 9

A developer is trying to create a FULLTEXT index on a column in an RDS MySQL instance. The error log shows the index creation failed. What is the most likely cause?

Accepted Answer

The column 'description' has a length that exceeds the maximum allowed for FULLTEXT index.. In RDS MySQL, FULLTEXT indexes have a maximum column length limit of 1000 bytes for InnoDB and 1000 characters for MyISAM. If the 'description' column exceeds this limit, the index creation will fail. This is the most likely cause because the error log indicates a failure without other configuration issues.

Answer

The table size is too large for a FULLTEXT index to be created.

Answer

The table uses a character set that is not compatible with FULLTEXT indexes.

Answer

The InnoDB engine does not support FULLTEXT indexes.

Question 10

A company is deploying an RDS MySQL database using the above CloudFormation template. After deployment, the database automatically reboots during the maintenance window. The company wants to reduce the impact of maintenance events. Which parameter change would minimize unavailability?

Accepted Answer

Set AutoMinorVersionUpgrade to true in the template.. Setting AutoMinorVersionUpgrade to true ensures that minor version upgrades are applied automatically during the maintenance window, but more importantly, it enables the use of a Multi-AZ deployment's automatic failover to reduce downtime. In a Multi-AZ RDS MySQL setup, the primary database reboots during maintenance, but the standby instance takes over with minimal interruption. This parameter change minimizes unavailability by leveraging the failover mechanism, whereas other options do not directly address the impact of maintenance reboots.

Answer

Increase BackupRetentionPeriod to 30 days to have more recovery points.

Answer

Increase AllocatedStorage to 500 GB to improve performance during maintenance.

Answer

Change PreferredMaintenanceWindow to a less busy time.

Question 11

A company is migrating an on-premises MySQL database to Amazon RDS for MySQL. The database has a large table with frequent inserts and updates. To minimize downtime during migration, which AWS service should be used?

Accepted Answer

AWS Database Migration Service (DMS). AWS Database Migration Service (DMS) is the correct choice because it supports ongoing replication (change data capture, CDC) from an on-premises MySQL source to Amazon RDS for MySQL, allowing the source database to remain fully operational during the migration. This minimizes downtime by continuously applying inserts and updates from the source to the target until you perform the final cutover, which can be a brief pause of seconds to minutes.

Answer

Amazon RDS read replica

Answer

AWS Schema Conversion Tool (SCT)

Answer

AWS Glue

Question 12

A gaming company uses Amazon DynamoDB with global tables across two regions. They notice increased write latency and throttling during peak hours. The access pattern is mostly writes to a small set of hot partitions. Which design change would best address this?

Accepted Answer

Implement write sharding using a random suffix on the partition key. The correct answer is A because the issue is hot partitions caused by a small set of partition keys receiving the majority of writes. By implementing write sharding with a random suffix on the partition key, you distribute writes across multiple partitions, reducing throttling and write latency. This directly addresses the root cause of uneven access patterns, unlike the other options that either cache reads, adjust capacity mode, or scale capacity without solving the partition-level bottleneck.

Answer

Enable DynamoDB Accelerator (DAX)

Answer

Switch to DynamoDB on-demand capacity mode

Answer

Increase write capacity using auto scaling

Question 13

A company needs to store JSON documents that are frequently accessed by a web application. The documents have varying attributes and the query pattern includes filtering on multiple fields. Which AWS database service is most suitable?

Accepted Answer

Amazon DynamoDB. Amazon DynamoDB is the most suitable choice because it is a fully managed NoSQL key-value and document database that natively supports JSON documents with varying attributes. Its flexible schema allows each item to have different attributes, and its support for secondary indexes (Local Secondary Indexes and Global Secondary Indexes) enables efficient filtering and querying on multiple fields without requiring predefined schemas or complex joins.

Answer

Amazon Neptune

Answer

Amazon ElastiCache for Redis

Answer

Amazon RDS for MySQL

Question 14

A company is building a real-time analytics dashboard from IoT sensor data. Data arrives as time-series with millions of writes per second. The dashboard queries the last hour of data with aggregations. Which database design is most cost-effective?

Accepted Answer

Amazon Timestream. Amazon Timestream is purpose-built for time-series data, offering automatic tiered storage (in-memory for recent data and magnetic for historical) and built-in aggregation functions optimized for time-based queries. This design handles millions of writes per second cost-effectively, as it eliminates the need for manual sharding or TTL management, and its serverless model charges only for data written and queried, making it ideal for real-time analytics on the last hour of IoT sensor data.

Answer

Amazon DynamoDB with TTL and DAX

Answer

Amazon Redshift with streaming ingestion

Answer

Amazon RDS for PostgreSQL with TimescaleDB extension

Question 15

A company uses Amazon RDS for PostgreSQL for its e-commerce platform. The application team reports increasing read latency on the primary instance during sales events. Which action should be taken to reduce read load on the primary?

Accepted Answer

Create one or more read replicas. Creating one or more read replicas offloads read traffic from the primary RDS for PostgreSQL instance, directly addressing the increased read latency during sales events. Read replicas are asynchronous replicas that can serve SELECT queries, reducing the load on the primary without requiring application changes to the write path. This is the standard AWS solution for scaling read-heavy workloads in RDS.

Answer

Enable Multi-AZ deployment

Answer

Migrate to Amazon DynamoDB

Answer

Increase the instance size of the primary