DBS-C01 Workload-Specific Database Design Practice Test 9 — 15 Questions

Question 1

A gaming company runs a leaderboard application on Amazon DynamoDB. The application experiences sudden spikes in read traffic during tournaments. The table uses on-demand capacity and the reads are eventually consistent. However, some users report stale data for several seconds. What is the most likely cause?

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

Accepted Answer

The application is using eventually consistent reads.. Eventually consistent reads in DynamoDB can return stale data for up to one second under normal conditions, but during sudden spikes in read traffic, the replication lag can extend to several seconds. The application is using eventually consistent reads, which trade immediate consistency for higher throughput and lower latency, making stale data more likely during high-traffic periods like tournaments.

Answer

The table is using on-demand capacity instead of provisioned capacity.

Answer

The table has a global secondary index (GSI) that is not updated synchronously.

Answer

The read capacity units are insufficient for the traffic spikes.

Question 2

A healthcare company stores patient records in Amazon DynamoDB. Each record includes a 'patient_id' (partition key) and 'visit_date' (sort key). The company needs to run ad-hoc queries to find all patients seen by a specific doctor within a date range. Which design approach minimizes cost and latency for this query pattern?

Accepted Answer

Create a global secondary index (GSI) with doctor_id as partition key and visit_date as sort key.. A Global Secondary Index (GSI) with doctor_id as the partition key and visit_date as the sort key allows efficient key-based queries for all patients seen by a specific doctor within a date range. This avoids full table scans and filter operations, minimizing both cost (read capacity units) and latency. DynamoDB can directly retrieve the indexed items without scanning the base table.

Answer

Query the base table using a filter expression on doctor_id.

Answer

Create a local secondary index (LSI) with doctor_id as sort key.

Answer

Use a Scan operation with a filter expression for doctor_id and visit_date.

Question 3

A company is designing a database for an IoT application that collects sensor data every second from millions of devices. The data is time-series and must be stored for 90 days, with occasional queries for recent data. Which AWS database solution is MOST cost-effective and performant?

Accepted Answer

Amazon Timestream. Amazon Timestream is purpose-built for time-series data, offering automatic storage tiering (in-memory for recent data and magnetic for historical data) and serverless scaling, which makes it the most cost-effective and performant choice for ingesting sensor data every second from millions of devices and retaining it for 90 days with occasional queries on recent data.

Answer

Amazon Redshift

Answer

Amazon DynamoDB with TTL to expire old data

Answer

Amazon RDS for MySQL with partitioning

Question 4

A company is using Amazon RDS for PostgreSQL for its transactional database. The application generates reports that query millions of rows, causing high CPU on the primary instance. The reports are not time-sensitive. What is the MOST cost-effective way to offload the reporting queries without affecting write performance?

Accepted Answer

Create an Amazon RDS Read Replica and direct reporting queries to the replica.. Creating an Amazon RDS Read Replica offloads reporting queries to a separate read-only instance, preventing CPU contention on the primary. Since the reports are not time-sensitive, the replica can handle the large queries without impacting write performance, and it is cost-effective because you only pay for the replica's compute and storage.

Answer

Use Amazon ElastiCache to cache report results.

Answer

Enable Multi-AZ to distribute reads to the standby instance.

Answer

Migrate reporting to Amazon Redshift.

Question 5

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 6

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).. 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 7

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 8

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 9

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.. 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 10

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.. 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 11

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.. 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 12

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.. 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 13

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 14

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. This prevents the need for a separate, manually scheduled maintenance event to apply these upgrades, thereby reducing the overall number of maintenance-related reboots and minimizing unavailability compared to the other options. Option B increases recovery points but does not reduce downtime; Option C improves performance but not maintenance impact; Option D shifts the downtime but does not reduce its length.

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 15

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