DBS-C01 Practice Test 49 — 15 Questions

Question 1

A company is building a real-time leaderboard for a mobile game using Amazon DynamoDB. The leaderboard displays the top 100 players by score. The table has 'game_id' as partition key and 'player_id' as sort key. The score is updated frequently. Which THREE design patterns should the company implement to ensure low-latency reads for the leaderboard? (Choose three.)

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

Accepted Answer

Enable DynamoDB Accelerator (DAX) to cache the leaderboard query.. Option B is correct because DAX is an in-memory cache for DynamoDB that delivers microsecond read latency for repeated, read-heavy queries like a frequently refreshed top-100 leaderboard, reducing the load on the base table. Option D is correct because a GSI with game_id as partition key and score as sort key lets you query a single game's players already ordered by score, so reading the top 100 requires only a Query with ScanIndexForward: false and Limit: 100 instead of scanning or sorting the whole table. Option E is correct because DynamoDB Streams captures item changes and a Lambda function can precompute and write the ranked leaderboard into a separate table, so reads hit a small, purpose-built table with minimal latency rather than aggregating scores on demand. Option A is not appropriate because ScanIndexForward: false on the base table only reverses the order of the player_id sort key, not the score, so it cannot return the highest scores. Option C is not appropriate because begins_with on the sort key filters by player_id prefix, not by numeric score range, and cannot produce a top-100-by-score ordering.

Answer

Use 'ScanIndexForward: false' on the base table to get top players.

Answer

Use 'begins_with' operator on the sort key to filter by score range.

Question 2

A company wants to run a MongoDB-compatible database on AWS with automated patching and backups. Which service should they choose?

Accepted Answer

Amazon DocumentDB (with MongoDB compatibility). Amazon DocumentDB with MongoDB compatibility is the correct choice because it is a fully managed, MongoDB-compatible database service that provides automated patching and backups. It supports the MongoDB wire protocol and drivers, allowing existing MongoDB applications to migrate with minimal changes while offloading administrative tasks like patching, backup, and replication to AWS.

Answer

Self-managed MongoDB on Amazon EC2

Answer

Amazon DynamoDB

Answer

Amazon RDS for MySQL

Question 3

A database administrator needs to monitor the number of connections to an Amazon RDS for PostgreSQL DB instance. Which Amazon CloudWatch metric should be used?

Accepted Answer

DatabaseConnections. The DatabaseConnections metric in Amazon CloudWatch directly reports the number of client connections to the RDS for PostgreSQL DB instance. This metric is published by the RDS service and reflects the count of active connections as seen by the database engine, making it the correct choice for monitoring connection counts.

Answer

CPUUtilization

Answer

WriteLatency

Answer

FreeableMemory

Question 4

A company is migrating a 1 TB SQL Server database to Amazon RDS for SQL Server. They want to use the native backup and restore feature. What must they do first?

Accepted Answer

Upload the backup file to an Amazon S3 bucket.. To use the native backup and restore feature for migrating a SQL Server database to Amazon RDS, you must first upload the backup file to an Amazon S3 bucket. RDS for SQL Server supports restoring from backup files stored in S3 via the `RESTORE DATABASE` command, using the `FROM URL` option that references the S3 bucket. This is the only supported method for native restore, as RDS does not allow direct file system access or FTP transfers.

Answer

Store the backup file on an EBS volume attached to the RDS instance.

Answer

Use FTP to transfer the backup file directly to the RDS instance.

Answer

Use the AWS Management Console to upload the backup file to the RDS instance.

Question 5

A company uses Amazon Aurora MySQL-Compatible Edition and needs to audit all SQL statements executed by database users. Which feature should be enabled?

Accepted Answer

Enable the database engine audit logs (advanced auditing).. Aurora MySQL supports advanced auditing through database engine audit logs. Option B is wrong because CloudTrail logs API calls, not SQL queries. Option C is wrong because RDS Enhanced Monitoring provides OS metrics, not SQL audit. Option D is wrong because database activity streams capture activity in near real-time but are designed for monitoring and not primarily for SQL audit logging; however, they can be used, but the most direct answer is advanced auditing.

Answer

Enable AWS CloudTrail data events for the DB instance.

Answer

Enable database activity streams.

Answer

Enable RDS Enhanced Monitoring.

Question 6

Which TWO actions can be taken to monitor the health of an Amazon DynamoDB table? (Choose 2.)

Accepted Answer

Enable Amazon CloudWatch metrics for the table. Option B is correct because DynamoDB automatically publishes CloudWatch metrics such as ConsumedReadCapacityUnits, ConsumedWriteCapacityUnits, and ThrottledRequests, and enabling/using these metrics is the primary way to monitor table health and performance. Option E is correct because creating CloudWatch alarms on the ThrottledRequests metric (and related metrics like ReadThrottleEvents/WriteThrottleEvents) lets you detect and be notified when the table is being throttled, which directly reflects table health. Option A is not correct because AWS Trusted Advisor does not monitor DynamoDB table health or table limits in this manner. Option C is not correct because DynamoDB Streams with Lambda is used for change data capture and event-driven processing, not health monitoring. Option D is not correct because DAX is an in-memory caching layer that improves read response times, not a health-monitoring mechanism.

Answer

Use AWS Trusted Advisor to check table limits

Answer

Enable DynamoDB Streams and process events with AWS Lambda

Answer

Use DynamoDB Accelerator (DAX) to improve response times

Question 7

A company wants to enforce encryption in transit for all connections to their ElastiCache for Redis cluster. Which security measure should they implement?

Accepted Answer

Enable Encryption in-transit when creating the cluster.. ElastiCache for Redis enforces encryption in transit by enabling the feature at cluster creation time. This uses TLS to encrypt data moving between clients and the Redis nodes, ensuring that all connections are secured against eavesdropping or man-in-the-middle attacks. The setting cannot be changed after the cluster is provisioned, so it must be enabled during the initial setup.

Answer

Set a parameter group with 'require_secure_transport' to ON.

Answer

Use VPC Flow Logs to monitor connections.

Answer

Enable encryption at rest using KMS.

Question 8

Which TWO AWS services can be used to implement a serverless database architecture for variable workloads?

Accepted Answer

Amazon Aurora Serverless v2. Amazon Aurora Serverless v2 (B) is correct because it automatically scales database capacity up and down in fine-grained increments based on actual workload demand, and it is a fully managed serverless relational database that requires no capacity provisioning, making it ideal for variable workloads. Amazon DynamoDB (E) is correct because it is a fully managed, serverless NoSQL database that scales throughput and storage automatically on demand, with no servers to manage, perfectly suiting unpredictable or variable workloads. Amazon Redshift (A) is not correct because it is a provisioned data warehouse service (with Redshift Serverless as a separate offering) designed for analytical workloads rather than a general serverless database architecture. Amazon RDS Proxy (C) is not correct because it is a connection pooling and management layer for RDS/Aurora, not a database itself, and it does not provide serverless database capacity. Amazon ElastiCache (D) is not correct because it is a managed in-memory caching service (Redis/Memcached) that requires provisioned nodes and is used to accelerate reads, not to serve as a serverless database.

Answer

Amazon Redshift

Answer

Amazon RDS Proxy

Answer

Amazon ElastiCache

Question 9

A company is migrating an on-premises MongoDB database to Amazon DocumentDB (with MongoDB compatibility). Which AWS service can perform the migration with minimal downtime using ongoing replication?

Accepted Answer

AWS Database Migration Service (AWS DMS). AWS DMS supports MongoDB as a source and Amazon DocumentDB as a target, enabling live migration with ongoing replication via change data capture (CDC). This allows the company to migrate with minimal downtime by continuously applying changes from the source MongoDB to the target DocumentDB until cutover.

Answer

Amazon CloudWatch

Answer

AWS Schema Conversion Tool (AWS SCT)

Answer

AWS Glue

Question 10

A company is using Amazon DynamoDB Accelerator (DAX) to improve read performance. Recently, the cache hit ratio has dropped significantly. The application uses strongly consistent reads. What is the most likely cause of the low cache hit ratio?

Accepted Answer

The application is using strongly consistent reads, which bypass the DAX cache. DAX does not support strongly consistent reads. When an application issues a strongly consistent read, DAX bypasses the cache and sends the request directly to DynamoDB, resulting in a cache miss. If the application recently switched to or increased strongly consistent reads, the cache hit ratio would drop significantly.

Answer

The DynamoDB table's write capacity is too low

Answer

The DAX cluster has too few nodes

Answer

The DAX cluster's TTL is set too low

Question 11

A company runs an Amazon Aurora MySQL DB cluster with one writer and two readers. They notice that one reader instance is consistently showing higher than expected lag. The other reader is fine. What is the most likely cause?

Accepted Answer

The reader instance is being used for heavy analytical queries. Aurora MySQL uses a shared storage layer, so reader lag is typically caused by the reader's own workload, not by writer write volume. When a reader runs heavy analytical queries, it competes for CPU, memory, and buffer pool resources, delaying the apply of redo log records from the writer. The other reader remains unaffected because it has a lighter workload. Thus, the most likely cause is that the lagging reader is being used for heavy analytical queries.

Answer

The writer instance is experiencing high write activity

Answer

There is a network connectivity issue between the writer and that reader

Answer

The reader instance has a different DB parameter group

Question 12

A company is using Amazon DynamoDB and wants to monitor the read/write capacity utilization of a table. Which ONE AWS service can be used to set up alarms for capacity consumption?

Accepted Answer

Amazon CloudWatch. Amazon CloudWatch is the AWS service designed to monitor metrics and set alarms. DynamoDB automatically publishes metrics such as ConsumedReadCapacityUnits and ConsumedWriteCapacityUnits to CloudWatch. You can create CloudWatch alarms on these metrics to trigger actions when capacity utilization exceeds thresholds, enabling proactive management of table performance.

Answer

Amazon DynamoDB Auto Scaling

Answer

AWS CloudTrail

Answer

Amazon CloudWatch Logs

Answer

AWS Config

Question 13

A team manages an Amazon Aurora MySQL database. They observe that the 'Deadlocks' metric in CloudWatch is spiking. The application uses a single writer instance and multiple read replicas. Which action is most effective at reducing deadlocks?

Accepted Answer

Review application code to ensure transactions are as short as possible and access tables in a consistent order.. Deadlocks in Aurora MySQL occur when two or more transactions hold locks that the other needs, and they wait indefinitely. The most effective way to reduce deadlocks is to keep transactions short and access tables in a consistent order, which minimizes lock contention and avoids circular wait conditions. This directly addresses the root cause of deadlocks, unlike scaling or redirecting traffic, which only reduce the probability of contention without fixing the underlying locking pattern.

Answer

Increase the instance size to handle more concurrent connections.

Answer

Redirect read traffic to read replicas to reduce load on the writer.

Answer

Enable Multi-AZ to distribute the load.

Question 14

A company uses Amazon Redshift for its data warehouse. The security team wants to encrypt the data at rest and ensure that only authorized users can access the encryption keys. Which AWS service should be used to manage the encryption keys?

Accepted Answer

AWS Key Management Service (KMS). AWS Key Management Service (KMS) is the native AWS service for creating, rotating, and controlling access to encryption keys used by services like Amazon Redshift. Redshift integrates directly with KMS for encryption at rest, and IAM policies plus key policies restrict who can use the keys. This satisfies both encryption and authorized-access requirements.

Answer

AWS CloudHSM

Answer

AWS Secrets Manager

Answer

AWS Systems Manager Parameter Store

Question 15

A database engineer is reviewing Amazon RDS for MySQL error logs and sees repeated authentication failures from the same IP address. The application team confirms the password is correct. What is the most likely cause of these errors?

Accepted Answer

The user 'app_user' does not have access from host '10.0.1.50'. The error logs show authentication failures despite the password being correct, which indicates the issue is not with the password itself but with the host-based access control. In MySQL, user accounts are defined as 'user'@'host', and if the application is connecting from an IP address (e.g., 10.0.1.50) that is not included in the user's allowed hosts, MySQL will reject the connection with an authentication error even if the password is correct. This is a common misconfiguration when migrating or scaling applications across different subnets.

Answer

The password is incorrect

Answer

The 'app_user' account is locked

Answer

The database requires SSL connections