DBS-C01 Practice Test 39 — 15 Questions

Question 1

A startup is using Amazon DynamoDB for a gaming leaderboard. The table has a partition key of 'game_id' and a sort key of 'score'. The application frequently queries the top 10 scores for a given game. Recently, users have reported that the leaderboard is showing stale data. The DBA checks the CloudWatch metrics and sees no throttling. The table has auto scaling enabled. The application uses eventual consistent reads. The DBA suspects that the issue is related to write conflicts. What should the DBA do to ensure the leaderboard shows the most recent data?

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

Accepted Answer

Modify the application to use strongly consistent reads for leaderboard queries.. Strongly consistent reads return the most up-to-date data from DynamoDB, ensuring the leaderboard displays the latest scores. Option B is incorrect because DynamoDB Streams capture changes but do not affect read consistency. Option C is incorrect because DAX is a caching layer that may serve stale data, not improve consistency. Option D is incorrect because write capacity adjustments do not address read consistency issues.

Answer

Enable DynamoDB Streams and process updates in near-real-time.

Answer

Enable DynamoDB Accelerator (DAX) for caching.

Answer

Increase the write capacity units to reduce write throttling.

Question 2

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The security team requires that all data be encrypted at rest using a customer-managed KMS key. Additionally, the database should be accessible only from a specific VPC. Which THREE steps should the database specialist take to meet these requirements? (Choose three.)

Accepted Answer

Configure the security group for the RDS instance to allow inbound traffic only from the application security group.. Security groups act as a virtual firewall for RDS instances. By configuring the security group to allow inbound traffic only from the application security group, you restrict database access to specific application servers, meeting the requirement that the database be accessible only from a specific VPC.

Answer

Create a VPC endpoint for RDS and associate it with the DB instance.

Answer

Store the encryption key in Amazon S3 and configure RDS to use it.

Question 3

A company uses Amazon DynamoDB for a session management workload. The access pattern is random and requires single-digit millisecond latency. The table has a read capacity of 5000 RCU. During peak hours, read requests occasionally exceed this capacity, causing throttling. Which design change is most appropriate to handle traffic spikes?

Accepted Answer

Enable DynamoDB auto scaling for reads.. DynamoDB auto scaling allows the table to dynamically adjust its provisioned read capacity (RCU) in response to traffic spikes, preventing throttling while maintaining single-digit millisecond latency. This is the most appropriate design change for a session management workload with random access patterns, as it handles occasional bursts without requiring manual intervention or architectural changes.

Answer

Switch to DynamoDB on-demand mode.

Answer

Add a global secondary index with different partition key.

Answer

Add a DAX cluster to cache read requests.

Question 4

A company is using Amazon DynamoDB for a gaming application. The application stores player scores in a table with a partition key of player_id and a sort key of timestamp. The company wants to query the top 10 scores for a given player efficiently. Which TWO steps should the company take to optimize this query?

Accepted Answer

Use the Query API with the LSI and scan index forward set to false to get the top scores.. The correct answers are A and B. A local secondary index (LSI) on the score attribute (option B) allows efficient sorting of items within the same partition key (player_id) by score. Using the Query API on this LSI with scanIndexForward set to false (option A) retrieves the top scores in descending order. Option C (Scan with filter) is inefficient as it reads the entire table. Option D (LSI on timestamp) is redundant because the base table already has timestamp as sort key and does not sort by score. Option E (GSI on score) would not be efficient for per-player queries because you would need to query by score globally, not per player.

Answer

Use a Scan operation with a filter expression to retrieve the top scores.

Answer

Create a local secondary index on the timestamp attribute.

Answer

Create a global secondary index (GSI) on the score attribute.

Question 5

Arrange the steps to perform a point-in-time recovery (PITR) for an Amazon RDS for MySQL DB instance in the correct order.

Accepted Answer

Identify the desired recovery time, then initiate the restore operation specifying the source DB instance and target time, then monitor the restore progress until the new DB instance is available, then verify the data in the restored instance.. PITR restores the database to a specific time within the backup retention window by selecting the restore option and specifying the time.

Answer

Identify the desired recovery time, then monitor the restore progress, then initiate the restore, then verify the data.

Answer

Initiate the restore operation, then identify the desired recovery time, then monitor the restore progress, then verify the data.

Answer

Identify the desired recovery time, then initiate the restore, then verify the data, then monitor the restore progress.

Question 6

Match each database engine to its default port number.

Accepted Answer

MySQL: 3306. The default ports are: MySQL on 3306, PostgreSQL on 5432, Oracle on 1521, and SQL Server on 1433. Common confusions include swapping MySQL and PostgreSQL ports.

Answer

MySQL: 5432

Answer

PostgreSQL: 3306

Question 7

A company is deploying a new application that requires a highly available DynamoDB table with eventual consistency. The table will be accessed from multiple AWS Regions. What is the most appropriate deployment strategy?

Accepted Answer

Use DynamoDB global tables. DynamoDB global tables provide a fully managed, multi-Region, multi-active solution that automatically replicates data across selected AWS Regions, delivering eventual consistency and high availability for applications accessed from multiple Regions. This is the most appropriate strategy because it natively supports the requirement without custom code or additional infrastructure.

Answer

Use DynamoDB auto scaling to handle regional traffic

Answer

Use DynamoDB Accelerator (DAX) to cache data across regions

Answer

Use DynamoDB Streams to replicate data to another region

Question 8

A company is running a MySQL database on Amazon RDS for a customer relationship management (CRM) application. The database has a table named 'contacts' with over 100 million rows. The application frequently runs queries to find contacts by email address. The email column has a B-tree index. Recently, the application started experiencing slow query performance. The team checked CloudWatch metrics and saw that the ReadIOPS for the RDS instance is consistently at 80% of the provisioned IOPS limit. The instance type is db.r5.large with 3000 provisioned IOPS (gp2). The buffer pool hit ratio is 95%. What is the most cost-effective design change to improve query performance?

Accepted Answer

Upgrade the RDS instance to db.r5.xlarge with 6000 provisioned IOPS.. Upgrading to a db.r5.xlarge with 6,000 provisioned IOPS (gp2) doubles the IOPS capacity, directly addressing the high ReadIOPS utilization (80%) without requiring application changes. This is the most cost-effective solution as it leverages the existing RDS infrastructure. Option B is wrong because migrating to DynamoDB would require significant application rework and is not necessary when the bottleneck is IOPS. Option C is wrong because OpenSearch adds unnecessary complexity and cost for a simple email lookup. Option D is wrong because the buffer pool hit ratio is already at 95%, indicating that increasing memory would yield minimal benefit.

Answer

Migrate the contacts table to Amazon DynamoDB with email as partition key.

Answer

Implement an Amazon OpenSearch Service cluster for email search.

Answer

Increase the buffer pool size by changing to a memory-optimized instance.

Question 9

A database engineer is troubleshooting high CPU usage on an Amazon RDS for PostgreSQL instance. Amazon CloudWatch shows CPU Utilization consistently above 90% during business hours. Which combination of actions should the engineer take to identify the root cause? (Choose TWO.)

Accepted Answer

Review the slow query log to identify long-running queries.. Reviewing the slow query log directly identifies long-running queries that can cause sustained high CPU usage on RDS for PostgreSQL. Option D is correct because Performance Insights provides a visual dashboard of database load and top SQL queries, making it easy to pinpoint which queries are consuming the most CPU resources.

Answer

Enable Enhanced Monitoring and review OS process list.

Answer

Scale up the DB instance to a larger instance class.

Answer

Install pg_stat_statements extension and query it.

Question 10

A company wants to migrate a self-hosted MongoDB database to Amazon DocumentDB. They need to convert the schema. Which AWS service should they use?

Accepted Answer

AWS Schema Conversion Tool (SCT). AWS Schema Conversion Tool (SCT) is the correct choice because it is specifically designed to convert database schemas from one engine to another, including from MongoDB to Amazon DocumentDB. SCT analyzes the source schema, identifies incompatible objects, and generates a target schema that is compatible with DocumentDB, handling data type mappings, index conversions, and other structural differences.

Answer

AWS Glue

Answer

AWS Database Migration Service (DMS)

Answer

Amazon Athena

Question 11

A company is deploying a new Amazon RDS for PostgreSQL DB instance. Which THREE actions are recommended for a secure deployment?

Accepted Answer

Enable encryption at rest using AWS KMS. Enabling encryption at rest using AWS KMS ensures that the underlying storage for the RDS for PostgreSQL DB instance is encrypted using AES-256 encryption. This protects data at rest against unauthorized physical access to the storage media and is a fundamental security best practice. KMS integration also allows for centralized key management and audit trails via AWS CloudTrail.

Answer

Use the default VPC for simplicity

Answer

Delete automated backups after the initial snapshot to reduce costs

Question 12

Which TWO actions can help protect an RDS database from SQL injection attacks? (Choose 2.)

Accepted Answer

Use parameterized SQL statements in the application.. Parameterized SQL statements (also known as prepared statements) ensure that user input is treated strictly as data, not executable code, preventing SQL injection at the application layer. Option E is correct because input validation and sanitization filter out malicious characters or patterns before they reach the database, adding an extra layer of defense. Both measures are essential; network controls (security groups) and encryption do not prevent injection attacks.

Answer

Enable Multi-AZ for the RDS instance.

Answer

Enable encryption at rest using KMS.

Answer

Restrict network access using security groups.

Question 13

A company runs a critical e-commerce platform on Amazon Aurora MySQL. The database is 2 TB and experiences a sudden spike in write latency during flash sales. The application uses auto-generated UUIDs as primary keys. The CPU utilization on the writer instance is 80%, and the read replicas show low utilization. Write latency has increased from 5 ms to 200 ms. The company needs to reduce write latency with minimal application changes. Which course of action is MOST effective?

Accepted Answer

Change the primary key to an auto-increment BIGINT and recreate indexes.. B is correct because UUID primary keys cause random writes that fragment the B-tree index, leading to frequent page splits and high write latency. Changing to an auto-increment BIGINT allows sequential writes, which fill index pages contiguously and reduce the write amplification that drives latency from 5 ms to 200 ms. This requires no application logic changes beyond the schema migration, making it the most effective minimal-change solution.

Answer

Implement sharding across multiple Aurora clusters.

Answer

Add more read replicas and redirect write-heavy queries to replicas.

Answer

Upgrade the writer instance to a larger instance type with more IOPS.

Question 14

A gaming company wants to store player profiles and game state data with low-latency access for millions of concurrent users. The data is accessed via a REST API and requires high scalability with minimal operational overhead. Which 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 delivers single-digit millisecond latency at any scale, making it ideal for storing player profiles and game state data for millions of concurrent users. It supports high throughput with auto-scaling, integrates seamlessly with REST APIs via AWS SDKs, and requires minimal operational overhead due to its serverless nature.

Answer

Amazon RDS for MySQL with read replicas

Answer

Amazon Neptune

Answer

Amazon ElastiCache for Redis

Question 15

A company is migrating an on-premises Oracle database to Amazon Aurora PostgreSQL. The database is 2 TB and has a daily change rate of 10%. They have a 1 Gbps network connection to AWS. They want to minimize downtime during the migration. Which migration approach should they use?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication. AWS DMS with ongoing replication (change data capture) is the correct choice because it allows continuous replication of changes from the source Oracle database to the target Aurora PostgreSQL, minimizing downtime by keeping the target nearly in sync until a final cutover. The 2 TB size and 10% daily change rate make a full offline export impractical, and DMS handles both schema conversion (via SCT integration) and data migration with minimal interruption.

Answer

Use AWS Schema Conversion Tool (SCT) to convert schema, then import data

Answer

Use pg_dump to export the database and pg_restore to import

Answer

Create an Aurora read replica from the Oracle database