DBS-C01 Practice Test 24 — 15 Questions

Question 1

A company needs to store and query graph data (nodes and edges) for a social network. They require low-latency traversals. Which AWS database is best suited?

Accepted Answer

Amazon Neptune. Amazon Neptune is a fully managed graph database service optimized for storing and querying highly connected data, such as social network nodes and edges. It supports both property graph (Gremlin) and RDF (SPARQL) models, enabling low-latency traversals of complex relationships. This makes it the ideal choice for workloads requiring efficient graph queries over interconnected data.

Answer

Amazon RDS for MySQL

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Amazon ElastiCache for Redis

Answer

Amazon DynamoDB

Question 2

A company runs a production Amazon RDS for PostgreSQL database. The database specialist needs to perform a major version upgrade with minimal downtime. Which strategy should the specialist use?

Accepted Answer

Create a read replica with the new major version, promote it to primary, and update the application connection string.. Creating a read replica with the new major version, promoting it to primary, and updating the application connection string minimizes downtime by allowing the replica to catch up with the source database before promotion. This approach avoids the prolonged unavailability associated with in-place upgrades, as the promotion process typically takes only a few seconds, and the application can be switched over with a simple connection string update.

Answer

Take a snapshot of the database, launch a new instance from the snapshot, and upgrade it.

Answer

Modify the DB instance to the new version directly using the AWS Management Console.

Answer

Schedule a maintenance window during off-peak hours and apply the upgrade.

Question 3

A company is deploying an Amazon RDS for MySQL database in a VPC. The database must be accessible only from a specific set of application servers in the same VPC. Which configuration provides the most secure access?

Accepted Answer

Set the security group inbound rule to reference the security group of the application servers. Referencing the application servers' security group as the source in the RDS inbound rule allows traffic only from those specific instances, regardless of IP changes. This follows the AWS security best practice of using security group IDs for fine-grained, stateful access control within a VPC, eliminating reliance on static IP addresses or CIDR ranges.

Answer

Set the security group inbound rule to allow all traffic from the VPC CIDR

Answer

Place the RDS instance in a separate subnet group

Answer

Set the RDS instance to publicly accessible

Question 4

A company is planning to migrate a 1 TB SQL Server database to Amazon RDS for SQL Server. Which TWO factors should be considered when choosing the migration approach?

Accepted Answer

The need to modify the database schema for compatibility. When migrating a SQL Server database to Amazon RDS, certain features like full-text search, CLR assemblies, or deprecated data types may not be supported or require schema modifications. RDS for SQL Server does not support all SQL Server features (e.g., FileStream, Service Broker, or cross-database references), so the schema must be reviewed and potentially altered to ensure compatibility before migration.

Answer

The number of concurrent users accessing the database

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Whether the database uses SQL Server Agent jobs

Answer

The version of the source SQL Server instance

Question 5

A company uses Amazon RDS for MySQL with Multi-AZ deployment. The primary instance fails and the database administrator notices that the failover did not happen automatically. What is the MOST likely cause?

Accepted Answer

The DB instance is configured as a read replica.. A read replica in Amazon RDS for MySQL is a separate DB instance that asynchronously replicates from a source instance. It does not support automatic failover; if the source instance fails, the read replica remains a standalone read-only instance and does not become the primary. Multi-AZ failover only occurs between a primary and its standby in the same region, not to a read replica.

Answer

The DB instance is in a public subnet.

Answer

Enhanced Monitoring is disabled.

Answer

The standby instance is in a different VPC.

Question 6

A company has an Amazon RDS for MySQL database with Multi-AZ deployment. The database is experiencing high CPU utilization due to a reporting workload. The company wants to migrate to Amazon Aurora MySQL to improve performance and scalability. The migration must have minimal downtime. Which migration strategy meets these requirements?

Accepted Answer

Create an Aurora MySQL replica from the RDS MySQL instance and promote it. Creating an Aurora MySQL replica from an existing RDS MySQL instance uses the native MySQL replication protocol to perform an online migration with minimal downtime. Once the replica is fully synchronized, you can promote it to become a standalone Aurora cluster, which provides better performance and scalability for the reporting workload.

Answer

Take a snapshot of the RDS instance and restore it to an Aurora cluster

Answer

Migrate to a larger RDS MySQL instance to handle the workload

Answer

Use AWS DMS with full load and ongoing replication

Question 7

A developer reports that an application is unable to connect to an Amazon RDS for MySQL DB instance. The security group for the DB instance allows inbound traffic on port 3306 from the application server's security group. The DB instance is in a VPC with both public and private subnets. The application server is in a private subnet. What is the most likely cause of the connection failure?

Accepted Answer

The network ACL for the private subnet is blocking outbound traffic to the DB instance.. The most likely cause is that the network ACL (NACL) for the private subnet is blocking outbound traffic to the DB instance. Security groups are stateful and allow return traffic automatically, but NACLs are stateless and require explicit rules for both inbound and outbound. If the private subnet's NACL does not allow outbound traffic to the DB instance's subnet on port 3306, the application server cannot initiate the connection. Options A and B are incorrect because the security group already allows inbound traffic, and instances in public and private subnets within the same VPC can communicate via private IPs. Option D is incorrect; while a DB subnet group is required for RDS, it does not directly affect connectivity once the instance is running.

Answer

The DB instance is in a public subnet and the application server is in a private subnet, so they cannot communicate.

Answer

The security group for the DB instance does not allow inbound traffic from the application server's security group.

Answer

The DB instance is not part of a DB subnet group that includes the private subnet.

Question 8

A company has an Amazon DynamoDB table with on-demand capacity mode. The table experiences occasional spikes in traffic. During these spikes, some requests receive ProvisionedThroughputExceededException errors. The company wants to minimize these errors without changing the application. Which solution should be used?

Accepted Answer

Switch the table to provisioned capacity mode and enable auto scaling.. DynamoDB on-demand mode automatically scales based on traffic volume, but it has a per-partition throughput limit. During sudden traffic spikes, this limit can be exceeded, causing ProvisionedThroughputExceededException errors. Switching to provisioned capacity mode with auto scaling allows you to set a higher baseline capacity and automatically scale up to handle bursts, reducing the likelihood of hitting per-partition limits. Option B (DAX) only helps with read caching, not write throughput. Option C (manually increasing capacity) is not applicable in on-demand mode and would not auto-scale. Option D (global tables) replicates data across regions for disaster recovery, not for increasing throughput in a single region.

Answer

Enable DynamoDB Accelerator (DAX) for caching.

Answer

Increase the read and write capacity units manually.

Answer

Use DynamoDB global tables to distribute the load across multiple regions.

Question 9

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 10

A company is deploying a new web application using Amazon RDS for PostgreSQL. The application requires read-heavy workloads and automatic failover. Which configuration should be used?

Accepted Answer

Multi-AZ deployment with one or more Read Replicas. A Multi-AZ deployment provides automatic failover to a standby instance in a different Availability Zone, ensuring high availability. Adding one or more Read Replicas offloads read-heavy workloads from the primary instance, improving performance. This combination meets both the read-heavy and automatic failover requirements for the application.

Answer

Multi-AZ deployment without Read Replicas

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Single-AZ with a Read Replica in the same region

Answer

Multiple Read Replicas in different regions

Question 11

Refer to the exhibit. An IAM policy is attached to a user. What is the effect when the user attempts to delete the RDS DB instance named 'prod-db'?

Accepted Answer

The user cannot delete the instance because of the explicit Deny statement.. The policy explicitly denies the rds:DeleteDBInstance action on the specific resource. Even though there is an Allow on other actions, an explicit Deny overrides any Allow. The user cannot delete the instance. Option A is wrong because the Deny takes precedence. Option B is wrong because the policy explicitly prevents deletion. Option D is wrong because the Deny is on the specific instance.

Answer

The user can delete any other instance except 'prod-db'.

Answer

The user can delete the instance because the Deny statement only applies to snapshots.

Answer

The user can delete the instance because of the Allow on DescribeDBInstances.

Question 12

A company is building a real-time chat application using Amazon DynamoDB. Each message has a conversation ID, timestamp, sender, and content. The primary access pattern is to retrieve the most recent 50 messages for a given conversation, ordered by timestamp. Which table design minimizes cost and latency?

Accepted Answer

Use conversation ID as partition key and timestamp as sort key; query with ScanIndexForward=false and Limit=50.. Using conversation ID as the partition key and timestamp as the sort key allows a single Query operation with ScanIndexForward=false to retrieve items in reverse chronological order, and Limit=50 ensures only the most recent 50 messages are returned. This design minimizes cost by avoiding full table scans or additional indexes, and minimizes latency by leveraging DynamoDB's native sort key ordering without needing external caching or streams.

Answer

Use a composite primary key of conversation ID and message ID, and enable DynamoDB Streams to process messages.

Answer

Use DynamoDB Accelerator (DAX) to cache the most recent messages.

Answer

Use conversation ID as partition key and a GSI on timestamp.

Question 13

A company has a document database workload on Amazon DynamoDB that stores user session data. The application frequently updates session attributes (e.g., last activity timestamp). The current design stores the entire session as a single item and updates the entire item on each session activity. This is causing high write costs and throttling. Which design pattern would reduce write costs and improve performance?

Accepted Answer

Use UpdateItem with an update expression to modify only the changed attributes.. Using UpdateItem with an update expression allows you to modify only the specific attributes that changed (e.g., last activity timestamp) instead of rewriting the entire item. This reduces write consumption to a fraction of the original cost, since DynamoDB charges based on the size of the written data, and partial updates write only the changed attribute bytes. This directly addresses the high write costs and throttling caused by full-item overwrites.

Answer

Increase the write capacity units (WCUs) on the table.

Answer

Implement DynamoDB Accelerator (DAX) to cache the session data.

Answer

Split the session item into multiple items, one per attribute.

Question 14

A company uses Amazon RDS for MySQL to store e-commerce order data. The orders table has millions of rows and is frequently queried by order_id. The company also runs periodic reports that aggregate data by order_date. The reports are slow. The database has a primary key on order_id. The company needs to improve report performance without affecting OLTP queries. Which design change should be made?

Accepted Answer

Create a secondary index on order_date.. Creating a secondary index on order_date allows MySQL to quickly locate rows matching the report's date range without scanning the entire table, significantly improving aggregation performance. This index is separate from the primary key on order_id, so OLTP queries that filter by order_id remain unaffected. The index provides a balanced approach: it accelerates read-heavy reporting while adding minimal overhead to write operations.

Answer

Upgrade to a larger instance type.

Answer

Create a read replica and run reports on the replica.

Answer

Partition the table by order_date.

Question 15

A developer is troubleshooting slow queries in Amazon RDS for MySQL. The 'Threads_running' status variable is consistently above 200. The application uses connection pooling. Which metric should be monitored to identify the root cause?

Accepted Answer

Innodb_row_lock_current_waits. High 'Threads_running' consistently above 200 often indicates queries waiting on locks or I/O. 'Innodb_row_lock_current_waits' directly measures the number of row lock waits, which is a common cause of blocked queries when connection pooling is used. Option B is wrong because 'Queries_per_second' measures throughput, not concurrent active queries. Option C is wrong because 'Slow_queries' counts only queries exceeding a time threshold, not all concurrent queries. Option D is wrong because 'Threads_connected' shows the number of open connections, not necessarily active queries; with connection pooling, many connections may be idle.

Answer

Queries_per_second

Answer

Slow_queries

Answer

Threads_connected