DBS-C01 Workload-Specific Database Design Practice Test 4 — 15 Questions

Question 1

A social media analytics company uses Amazon DynamoDB as the primary data store for user session data. Each session record has a partition key of user_id (String) and a sort key of session_start_time (Number, epoch). The application often queries the most recent 10 sessions for a given user. The traffic pattern shows that 90% of reads are for the last 10 sessions, while 10% are for historical sessions. The table has a provisioned read capacity of 5000 RCU and consistently experiences throttled read requests during peak hours. The company wants to optimize read performance without changing the provisioned capacity. Which design change will MOST improve read performance for this workload?

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

Accepted Answer

Create a Global Secondary Index (GSI) with the same partition key and a sort key of session_start_time, but query with ScanIndexForward=false and Limit=10.. Creating a GSI with the same partition key (user_id) and sort key (session_start_time) allows you to query with ScanIndexForward=false and Limit=10 to efficiently retrieve only the most recent 10 sessions per user. This avoids scanning all sessions for a user, reducing consumed read capacity and eliminating throttling without increasing provisioned RCU. The GSI also supports the 90% workload pattern by providing a targeted index that minimizes read unit consumption.

Answer

Increase the provisioned read capacity to 10000 RCU to handle the peak load.

Answer

Enable DynamoDB Accelerator (DAX) with default settings to cache the most recent sessions.

Answer

Configure Amazon ElastiCache for Redis as a read-through cache for session data.

Question 2

A gaming company uses Amazon RDS for PostgreSQL to store player profiles and game state data. The database is currently 500 GB and grows by 10 GB per day. The company runs weekly reports that scan the entire database, causing high I/O and CPU usage. The application experiences read latency spikes during report generation. The team wants to minimize performance impact on the application while maintaining the ability to run reports. Which solution should the team implement?

Accepted Answer

Create a read replica and direct all report queries to the read replica.. Creating a read replica for Amazon RDS for PostgreSQL allows the team to offload all report queries to a separate read-only endpoint, eliminating the I/O and CPU contention on the primary database. This directly addresses the read latency spikes during report generation without requiring any application changes beyond redirecting the reporting queries. The read replica asynchronously replicates data from the primary instance, ensuring the reports see a near-real-time snapshot of the data while the primary remains dedicated to the application workload.

Answer

Enable Multi-AZ deployment to provide a standby instance for failover and use it for reporting.

Answer

Scale up the RDS instance to a larger instance type to handle the additional load from reports.

Answer

Archive historical game state data to Amazon S3 and delete it from the database to reduce size.

Question 3

A financial services company uses Amazon DynamoDB to store transaction records. Each transaction has a unique transaction_id as the partition key and a timestamp as the sort key. The application frequently queries all transactions for a given customer within a date range. However, customer_id is not an attribute indexed for querying. The company wants to optimize these queries without redesigning the entire table schema. Which action should the company take?

Accepted Answer

Create a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key.. Creating a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key allows efficient querying of all transactions for a given customer within a date range without redesigning the base table. The GSI provides a new access pattern with its own partition and sort keys, enabling the Query operation on customer_id and timestamp, which is far more efficient than a Scan. This approach preserves the existing table schema and supports the required query pattern with minimal overhead.

Answer

Change the table's partition key to customer_id and use a composite sort key.

Answer

Create a Local Secondary Index (LSI) on customer_id.

Answer

Use the Scan operation with a filter expression for customer_id and timestamp.

Question 4

Arrange the steps to migrate an on-premises Oracle database to Amazon RDS for Oracle using AWS DMS (Database Migration Service) in the correct order.

Accepted Answer

Launch the DMS replication instance, then configure the source and target endpoints, then create the migration task, then monitor the migration task.. DMS migration requires setting up the replication instance, configuring endpoints with proper source database settings for CDC, creating a migration task, and monitoring for completion.

Answer

Configure the source and target endpoints, then launch the DMS replication instance, then create the migration task, then monitor the migration task.

Answer

Launch the DMS replication instance, then create the migration task, then configure the source and target endpoints, then monitor the migration task.

Answer

Configure the source and target endpoints, then launch the DMS replication instance, then monitor the migration task, then create the migration task.

Question 5

Arrange the steps to enable encryption at rest for an existing unencrypted Amazon RDS for MariaDB DB instance in the correct order.

Accepted Answer

Create a manual snapshot, then copy the snapshot with encryption enabled, then restore the encrypted snapshot to a new DB instance, then migrate applications.. Encryption at rest for an existing instance requires creating an encrypted snapshot and restoring it, then migrating applications.

Answer

Create a manual snapshot, then restore the snapshot to a new instance, then copy the new instance with encryption, then migrate applications.

Answer

Create a manual snapshot, then copy the snapshot with encryption, then modify the original DB instance to use encryption.

Answer

Enable encryption on the original DB instance via a maintenance window, then take a snapshot, then restore.

Question 6

Match each AWS service to its primary purpose.

Accepted Answer

RDS: Managed relational database service supporting multiple engines. These are core AWS database services with distinct use cases. Common confusions include mixing up Redshift (data warehouse) with ElastiCache (in-memory cache) and Neptune (graph) with DocumentDB (document).

Answer

Redshift: Fully managed in-memory caching service

Answer

ElastiCache: Fully managed petabyte-scale data warehouse

Answer

Neptune: Fully managed document database

Question 7

Match each RDS storage type to its description.

Accepted Answer

General Purpose SSD: Balanced price and performance, suitable for most database workloads.. Correct matches: General Purpose SSD balances price and performance; Provisioned IOPS SSD provides high, consistent performance; Magnetic is low-cost for infrequent access. Common confusions include swapping the descriptions of General Purpose and Provisioned IOPS, or associating low cost with Provisioned IOPS.

Answer

General Purpose SSD: High performance with consistent low latency.

Answer

Magnetic: Balanced price and performance.

Answer

Provisioned IOPS SSD: Lowest cost, suitable for infrequently accessed data.

Question 8

A company runs a customer-facing application on Amazon RDS for MySQL. The application experiences frequent read replicas lagging behind the primary due to long-running analytics queries. The analytics team runs complex SELECT queries that scan large tables. Which design change would minimize replica lag without affecting production writes?

Accepted Answer

Create a cross-Region read replica for analytics queries.. Creating a cross-Region read replica for analytics queries offloads the long-running SELECT statements to a separate read replica in a different AWS Region, isolating the analytics workload from the primary instance and its in-Region replicas. This prevents the analytics queries from competing for I/O and CPU resources on the primary or its local replicas, thereby minimizing replica lag without affecting production writes. Cross-Region replicas use asynchronous replication, so they can handle heavy read traffic without impacting the primary's write performance.

Answer

Use Amazon DynamoDB Accelerator (DAX) for caching.

Answer

Increase the instance size of the primary and all read replicas.

Answer

Enable Multi-AZ on the primary instance.

Question 9

A startup is building a real-time leaderboard for a mobile game using Amazon DynamoDB. The leaderboard must update frequently and support global access with low latency. Which database design approach is most suitable?

Accepted Answer

Use Amazon DynamoDB global tables with appropriate partition key design.. Amazon DynamoDB global tables provide multi-Region, fully managed, multi-master replication, which is ideal for a real-time leaderboard requiring frequent updates and low-latency global access. By designing an appropriate partition key (e.g., game ID or time-based composite key), you can distribute write traffic evenly and avoid hot partitions, ensuring consistent performance under high update frequency.

Answer

Use Amazon ElastiCache for Redis with replication across Regions.

Answer

Use Amazon Aurora Global Database with a single writer and multiple readers.

Answer

Use Amazon S3 with event notifications to update a leaderboard file.

Question 10

A company needs to store and query time-series data from IoT sensors. The data is written continuously and queried by time range for dashboards. Which AWS database service is most cost-effective and scalable for this workload?

Accepted Answer

Amazon Timestream.. Amazon Timestream is purpose-built for time-series data, offering automatic tiering between in-memory and magnetic stores for cost efficiency, and built-in functions for time-based aggregations and windowed queries. It is serverless and scales automatically to handle continuous writes from IoT sensors and low-latency dashboard queries by time range, making it the most cost-effective and scalable choice.

Answer

Amazon ElastiCache for Redis with time-series data structures.

Answer

Amazon DynamoDB with time-based partition keys.

Answer

Amazon RDS for PostgreSQL with time-based indexing.

Question 11

A company uses Amazon DynamoDB for a shopping cart application. During a flash sale, write requests are throttled due to hot partitions. The access pattern is evenly distributed across items, but the partition key is the customer ID. Which design change would best mitigate throttling?

Accepted Answer

Enable DynamoDB adaptive capacity.. DynamoDB adaptive capacity automatically adjusts throughput capacity based on traffic patterns, which helps mitigate hot partitions by redistributing unused capacity from less-accessed partitions to heavily accessed ones. This is ideal for the flash sale scenario where write requests are throttled due to uneven access across customer ID partitions, even though the overall access pattern is evenly distributed.

Answer

Change the partition key to a single value for all items.

Answer

Increase the provisioned write capacity to a higher fixed value.

Answer

Add a DAX cluster in front of DynamoDB.

Question 12

A company is migrating an on-premises MongoDB database to AWS. Which AWS database service is most compatible and requires minimal application changes?

Accepted Answer

Amazon DocumentDB (with MongoDB compatibility).. Amazon DocumentDB (with MongoDB compatibility) is the most compatible AWS database service for migrating an on-premises MongoDB database because it is purpose-built to emulate the MongoDB wire protocol and data model, allowing existing MongoDB drivers and tools to connect with minimal or no application code changes. This makes it the ideal choice for a lift-and-shift migration that preserves the document-oriented structure and query patterns of MongoDB.

Answer

Amazon DynamoDB.

Answer

Amazon Neptune.

Answer

Amazon RDS for MySQL.

Question 13

A company needs to implement a database solution for a global e-commerce platform that requires strongly consistent reads and writes with automatic failover across AWS Regions. Which service should be used?

Accepted Answer

Amazon Aurora Global Database.. Amazon Aurora Global Database is the correct choice because it provides strongly consistent reads and writes across multiple AWS Regions with automatic failover. It uses a primary cluster in one Region and up to five secondary read-only clusters in other Regions, with replication typically under one second. Failover to a secondary Region can be promoted in as little as one minute, meeting the requirements for a global e-commerce platform.

Answer

Amazon DynamoDB global tables.

Answer

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

Answer

Amazon ElastiCache for Redis with Global Datastore.

Question 14

A company runs a critical OLTP workload on Amazon RDS for PostgreSQL. The database size is 2 TB and growing. To reduce storage costs, the company wants to archive old data that is rarely accessed. Which approach is most cost-effective and minimally impacts performance?

Accepted Answer

Implement table partitioning and use S3 as an external table for old partitions.. It uses PostgreSQL table partitioning (e.g., range partitioning by date) combined with the `postgres_fdw` or `pg_parquet` extension to treat old partitions as foreign tables stored in Amazon S3. This keeps the hot data in RDS for fast OLTP access while offloading cold data to low-cost S3 storage, minimizing performance impact and reducing storage costs without requiring a full migration or schema redesign.

Answer

Move the database to Amazon Aurora PostgreSQL with storage auto-scaling.

Answer

Migrate the entire database to Amazon DynamoDB.

Answer

Delete old rows and run VACUUM FULL to reclaim space.

Question 15

A company runs an application that requires a relational database with high availability across multiple Availability Zones. The database must automatically failover with minimal downtime. Which AWS service meets these requirements?

Accepted Answer

Amazon RDS for MySQL with Multi-AZ deployment.. Amazon RDS for MySQL with Multi-AZ deployment automatically provisions and maintains a synchronous standby replica in a different Availability Zone. If the primary instance fails, Amazon RDS automatically fails over to the standby, typically within 60–120 seconds, providing high availability with minimal downtime. This meets the requirement for a relational database with automatic failover across multiple Availability Zones.

Answer

Amazon DynamoDB with global tables.

Answer

Amazon Redshift with cross-Region snapshots.

Answer

Amazon RDS for MySQL with a single instance.