DBS-C01 Practice Exam 52 — 20 Questions

Question 1

A financial services company runs a production Amazon Aurora MySQL database cluster (1 writer, 2 readers) in us-east-1. The database stores critical trading data. The company's disaster recovery policy requires an RPO of 5 seconds and an RTO of 1 minute for a regional failure. The current setup does not include any cross-region replication. The database is 5 TB in size. The operations team needs to implement a solution that meets the DR requirements with minimal cost and operational overhead. Which solution should the team implement?

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

Accepted Answer

Deploy an Aurora Global Database with a secondary cluster in us-west-2. Configure the secondary cluster as a failover target.. Aurora Global Database provides replication across regions with typical RPO of seconds and RTO of minutes. It is the most appropriate solution for low RPO/RTO with minimal overhead. Option B is correct. Option A (automated backups) have an RPO of 5 minutes, which exceeds the required 5 seconds. Option C (DMS) adds cost and complexity. Option D (cross-Region read replicas) can have replication lag exceeding 5 seconds.

Answer

Enable automated backups and configure cross-Region snapshot copy. Use point-in-time recovery in the secondary region.

Answer

Use AWS Database Migration Service (DMS) to continuously replicate changes to an Aurora cluster in us-west-2.

Answer

Create cross-Region read replicas in us-west-2 and set up a replication channel. In disaster, promote a replica.

Question 2

A company is migrating a 5 TB SQL Server database to Amazon RDS for SQL Server using AWS DMS. They are using Full LOB mode. The migration is failing with an error about memory allocation. What should they do to resolve this?

Accepted Answer

Increase the DMS replication instance class.. The memory allocation error in AWS DMS Full LOB mode occurs when the replication instance lacks sufficient memory to buffer LOB data. Increasing the replication instance class (option B) directly provides more memory, resolving the issue. Decreasing MaxLobSize (A) would truncate data, not fix allocation. Splitting the task (C) does not increase memory per instance. Enabling BatchApply (D) improves commit efficiency but does not address memory allocation for LOBs. Therefore, B is correct.

Answer

Decrease the MaxLobSize setting.

Answer

Split the migration into multiple DMS tasks.

Answer

Enable BatchApply on the DMS task.

Question 3

A media streaming company uses Amazon DynamoDB as the primary data store for user session information. The table has a partition key of 'user_id' (String) and a sort key of 'session_start_time' (Number). The table is provisioned with 5000 read capacity units (RCU) and 5000 write capacity units (WCU). Over the past week, the company noticed occasional throttling on writes during peak hours, even though the average consumed WCU is only 3500. The DynamoDB table also experiences hot partitions. The development team is considering using DynamoDB Accelerator (DAX) to cache read-heavy workloads, but the issue is with writes. The database administrator needs to resolve the write throttling and hot partitions. Which action should the administrator take?

Accepted Answer

Enable DynamoDB adaptive capacity to automatically handle uneven access patterns.. Adaptive capacity automatically adjusts throughput to handle uneven access patterns, helping with hot partitions. Option B is wrong because DAX caches reads, not writes; it does not help with write throttling. Option C is wrong because reducing WCU would worsen throttling, not resolve it. Option D is wrong because enabling auto scaling adjusts capacity but does not directly address hot partitions; it may help with overall throughput but not uneven distribution.

Answer

Deploy DAX to cache frequent writes and reduce write load.

Answer

Reduce the provisioned WCU to match the average consumption to save costs.

Answer

Enable DynamoDB auto scaling for write capacity to scale based on demand.

Question 4

A company is migrating a self-managed MongoDB database to Amazon DocumentDB. The database stores user profiles and activity logs. The activity logs are write-heavy and accessed infrequently. The company wants to optimize cost and performance for the workload. Which THREE design decisions should the company make?

Accepted Answer

Enable encryption at rest for both databases.. Enabling encryption at rest for Amazon DocumentDB is a security best practice that ensures data is encrypted using AWS Key Management Service (KMS) keys. This is a mandatory design consideration for compliance and data protection, and it does not significantly impact cost or performance for the workload described.

Answer

Use Amazon S3 for storing activity logs instead of DocumentDB.

Answer

Use a single DocumentDB cluster for both workloads with appropriate read replicas.

Question 5

A team is migrating an on-premises database to Amazon RDS using AWS DMS. After the full load completed, the task stopped. The team needs to perform ongoing replication to minimize downtime. What change should the team make to the DMS task?

Accepted Answer

Modify the replication task to change the migration type to 'full-load-and-cdc'.. After a full load completes and the task stops, the team needs to enable ongoing replication to capture and apply changes made to the source database during the migration window. Modifying the DMS task to use the 'full-load-and-cdc' migration type allows the task to perform the initial full load and then seamlessly transition to Change Data Capture (CDC) to replicate incremental changes, minimizing downtime. This is the correct approach because DMS supports switching a completed full-load task to include CDC without re-running the full load.

Answer

Restart the replication task with the same settings.

Answer

Create a new replication instance and start a new full-load task.

Answer

Use AWS Schema Conversion Tool to convert the schema again.

Question 6

A company is designing a database for a global e-commerce platform that requires low-latency reads and writes from multiple AWS regions. The data must be strongly consistent within a region but can be eventually consistent across regions. Which TWO services should the company consider?

Accepted Answer

Amazon DynamoDB Global Tables. Amazon DynamoDB Global Tables is correct because it provides a fully managed, multi-region, multi-active database solution that delivers low-latency reads and writes to globally distributed applications. It uses DynamoDB Streams to replicate data across regions with eventual consistency, meeting the requirement for strong consistency within a region and eventual consistency across regions.

Answer

Amazon ElastiCache for Redis Global Datastore

Answer

Amazon RDS Cross-Region Read Replicas

Answer

Amazon Redshift

Question 7

A company is using Amazon DynamoDB for a high-traffic web application. The table has on-demand capacity mode. During a marketing event, the application experiences throttling. Which TWO actions should the database specialist take to prevent throttling in future events?

Accepted Answer

Pre-create a DynamoDB global table to distribute write traffic.. Options C and E are correct. Option C: Pre-creating a DynamoDB global table can distribute write traffic across multiple regions, reducing the load on any single table and helping to prevent throttling during traffic spikes. Option E: Implementing DynamoDB Accelerator (DAX) offloads read traffic from the main table, reducing read capacity consumption and potential throttling. Option A is incorrect because on-demand mode does not use read capacity units; it scales automatically. Option B is incorrect because switching to provisioned capacity requires capacity planning and does not automatically prevent throttling. Option D is incorrect because decreasing write capacity would likely worsen throttling.

Answer

Increase the read capacity units of the table.

Answer

Switch the table to provisioned capacity mode and increase write capacity units.

Answer

Decrease the write capacity units to reduce throttling.

Question 8

A company is migrating a 500 GB PostgreSQL database from on-premises to Amazon Aurora PostgreSQL. The migration must be completed within 6 hours with minimal downtime. The on-premises network bandwidth is 500 Mbps. The team decides to use AWS DMS. During initial full load, DMS reports a 'Target metadata error: cannot write to Aurora' for a specific table. Investigation shows that the table has a trigger that tries to insert into an external web service. What should the team do to resolve this issue?

Accepted Answer

Disable the trigger on the target Aurora database during migration.. Disabling the trigger on the target Aurora PostgreSQL database during migration prevents the trigger from firing, which was causing the 'Target metadata error: cannot write to Aurora' error. The trigger's attempt to insert into an external web service is not compatible with DMS loading data. Option B is incorrect because increasing the DMS replication instance size does not address the trigger issue. Option C is incorrect because upgrading the DMS replication instance engine version does not address the trigger issue. Option D is incorrect because disabling the trigger on the source database does not prevent the trigger on the target from firing when DMS writes data; the error occurs on the target.

Answer

Increase the DMS replication instance size.

Answer

Upgrade the DMS replication instance engine version.

Answer

Disable the trigger on the source database.

Question 9

A company runs an online auction platform on AWS. The application uses Amazon DynamoDB as the primary database, with a table 'Auctions' that has a partition key 'auction_id' (String) and sort key 'end_time' (Number). The table also has a global secondary index (GSI) on 'status' (String) and 'current_bid' (Number). The application frequently queries for active auctions sorted by current bid. Recently, the team noticed that queries on the GSI for active auctions with a high current_bid are returning results slowly. The DynamoDB table has 10,000 write capacity units (WCU) and 30,000 read capacity units (RCU) provisioned. The GSI has 5,000 RCU provisioned. The team suspects throttling on the GSI. What is the most likely cause of the slow queries?

Accepted Answer

The GSI's provisioned RCU is insufficient due to hot partitions.. The GSI has 5,000 RCU provisioned, but if the GSI's partition key (status) and sort key (current_bid) lead to a hot partition—for example, many active auctions have the same status and similar current_bid—that single partition can throttle even if the total RCU is not fully utilized. This is because DynamoDB distributes RCU evenly across partitions, and a hot partition can exceed its allocated RCU, causing throttling on that partition. Option B is incorrect because the index key schema (status, current_bid) is actually appropriate for querying active auctions sorted by current bid; the issue is hot partitions, not inefficiency. Option C is incorrect because WCU throttling does not directly affect read performance on the GSI. Option D is incorrect because the table's RCU is separate from the index's RCU, and the index's RCU is the relevant factor.

Answer

The GSI key schema is inefficient for the query pattern.

Answer

The table's WCU is too low, causing throttling on writes that affects reads.

Answer

The table's RCU is too low for the application's read load.

Question 10

A company is migrating a 3 TB Oracle database from on-premises to Amazon RDS for Oracle. The migration must have zero downtime. The on-premises server uses Oracle Data Guard for disaster recovery. The network bandwidth is 200 Mbps. The team plans to use AWS DMS with CDC from Oracle redo logs. During the initial full load, DMS reports that the source table 'ORDERS' has a table-level supplemental log missing. The migration fails. What should the team do first to resolve this issue?

Accepted Answer

Enable supplemental logging on the Oracle source database for the 'ORDERS' table.. AWS DMS requires supplemental logging on the source Oracle tables to capture change data for CDC. Without it, DMS cannot track changes. Option A is incorrect because switching to Oracle GoldenGate would not address the root cause and adds complexity. Option B is incorrect because using AWS SCT and native export/import does not provide zero-downtime migration. Option D is incorrect because recreating the task with 'full load only' would lose the CDC requirement, causing downtime for ongoing changes.

Answer

Switch to Oracle GoldenGate for migration.

Answer

Use AWS SCT to convert the schema and then use a native export/import.

Answer

Recreate the DMS task with 'full load only' to bypass CDC.

Question 11

A company runs an e-commerce platform using Amazon Aurora MySQL with Multi-AZ deployment. The application has a read-heavy workload and uses a mix of SELECT and UPDATE queries. Recently, the company migrated from a db.r5.large to a db.r5.2xlarge instance class to handle increased traffic. However, after the migration, the CPU utilization remains high during peak hours, and the application's page load times have increased. The DBA notices that the 'Read IOPS' metric is high, but the 'Read Latency' metric is low. There is also a high number of 'Select' queries in the database. The application uses a single database endpoint. What should the DBA do to reduce CPU utilization and improve read performance?

Accepted Answer

Create one or more Aurora Replicas and modify the application to use read-only endpoints for SELECT queries.. Creating Aurora Replicas offloads read-only SELECT queries from the primary instance, reducing CPU utilization on the primary and improving overall read throughput. Option A is incorrect because enabling Multi-AZ with one standby replica provides high availability but does not help with read scaling; the standby is not used for reads. Option B is incorrect because Performance Insights is a monitoring tool that helps identify performance bottlenecks but does not directly reduce CPU utilization. Option C is incorrect because simply upgrading to a larger instance class may temporarily alleviate the issue but is not cost-effective and does not address the root cause of read-heavy workload imbalance; adding read replicas scales reads horizontally.

Answer

Enable Multi-AZ with one standby replica.

Answer

Enable Performance Insights and analyze the top SQL.

Answer

Upgrade the instance class to db.r5.4xlarge.

Question 12

A company has an Amazon RDS for SQL Server database that stores customer orders. The database is running on a db.m5.large instance. Recently, the DBA noticed that the 'Write IOPS' metric is consistently high during business hours, and the 'Write Latency' metric is also elevated. The application is experiencing slow order placement. The DBA checks the disk queue depth and finds it to be high. The database uses General Purpose SSD (gp2) storage with 500 GB. What should the DBA do to improve write performance?

Accepted Answer

Migrate to Provisioned IOPS (io2) storage with appropriate IOPS.. Provisioned IOPS (io2) storage provides consistent, high IOPS performance with low latency, which is needed when the workload exceeds the baseline IOPS of gp2 storage. The current gp2 volume at 500 GB provides only 1,500 baseline IOPS (3 IOPS per GB), which is insufficient for the high write IOPS during business hours, causing high write latency and disk queue depth. Option A is incorrect because Multi-AZ does not offload writes; it only provides high availability and may increase write latency due to synchronous replication. Option B is incorrect because while gp3 offers baseline performance with the ability to provision additional IOPS independently of storage size, it is still a general-purpose SSD; for consistent low latency under sustained high IOPS, io2 is more suitable. Option C is incorrect because increasing gp2 storage to 1,000 GB would increase baseline IOPS to 3,000, but this may not be enough, and it is more cost-effective to use io2 with the required IOPS rather than over-provisioning storage.

Answer

Enable Multi-AZ to offload writes to standby.

Answer

Change the storage type to gp3 and increase the IOPS.

Answer

Increase the storage size to 1000 GB to get more baseline IOPS.

Question 13

A company runs an e-commerce application on AWS using an Aurora MySQL database cluster. The security team mandates that all database audit logs must be stored in Amazon S3 for at least one year for compliance. The database is currently configured to publish audit logs to Amazon CloudWatch Logs. The security team wants to use AWS Database Migration Service (DMS) to migrate the database to a new Aurora MySQL cluster, and during the migration, the audit logs must continue to be captured uninterrupted. Which solution meets these requirements with the LEAST operational overhead?

Accepted Answer

Enable the Aurora MySQL advanced audit feature with file-based output, and configure the DMS task to use these log files as a source for ongoing replication.. Enabling the Aurora MySQL advanced audit feature allows audit logs to be output to files on the DB instance. These files can then be exported to Amazon S3 (e.g., via a scheduled script or Lambda function) for compliance. During the DMS migration, change data capture is handled by binary logs, not audit logs, so the audit logging remains uninterrupted. This approach minimizes operational overhead by using the built-in audit feature and a simple export mechanism, without requiring additional services like CloudTrail or Performance Insights.

Answer

Enable Performance Insights on the source cluster and export the data to S3.

Answer

Create an Aurora MySQL read replica and enable audit logs on the replica, then migrate from the replica.

Answer

Use AWS CloudTrail to capture SQL queries and deliver them to S3.

Question 14

A company recently migrated an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 100 GB and used by a web application. After migration, the application's response time increased. The 'ReadLatency' and 'WriteLatency' metrics are normal. The 'CPUUtilization' is at 90%. The 'DatabaseConnections' metric shows 200 connections, which is close to the max connections for the instance class (db.t3.medium, max connections = 200). The application uses connection pooling. The team wants to reduce CPU utilization without changing the application code. Which action should the team take?

Accepted Answer

Upgrade the DB instance to a larger class like db.t3.large.. Upgrading to a larger instance class, such as db.t3.large, provides more CPU resources (additional vCPUs), directly addressing the high CPU utilization (90%) while maintaining the same number of database connections. Option A is incorrect because decreasing 'max_connections' to 100 risks rejecting legitimate connections from the application's connection pool, potentially causing errors even though connection pooling is in use. Option B is incorrect because increasing allocated storage improves I/O throughput but does not reduce CPU utilization; the I/O latency metrics are already normal. Option D is incorrect because enabling Performance Insights adds monitoring overhead and switching to Provisioned IOPS improves I/O performance, but the bottleneck is CPU, not I/O.

Answer

Decrease 'max_connections' parameter to 100.

Answer

Increase allocated storage to 200 GB.

Answer

Enable Performance Insights and switch to Provisioned IOPS.

Question 15

A startup is deploying a new web application on AWS. The application uses Amazon RDS for PostgreSQL as its database. The developers need to create the initial schema and load test data. They have a SQL script file that creates tables and inserts 10,000 rows. The DB instance is a db.t3.micro with 20 GB gp2 storage. The developers connect to the RDS instance using pgAdmin from their local machine and run the script. The script fails with a 'connection reset' error after inserting 5,000 rows. What is the MOST likely cause?

Accepted Answer

The security group blocked the connection due to a timeout. The most likely cause is that the connection was terminated by an idle timeout on an intermediate network component (such as a NAT Gateway, which has a default idle timeout of 350 seconds, or the client-side firewall/proxy). Security groups are stateful and do not have configurable timeout settings, so they are not directly responsible. The script's duration likely exceeded the idle timeout, causing a 'connection reset' error. Option A is unlikely because a db.t3.micro can handle inserting 10,000 rows without exhausting memory or CPU credits; the error is network-related, not resource-related. Option B is incorrect because max_connections is sufficient for a single connection. Option C is incorrect because 20 GB storage is far more than needed for 10,000 rows.

Answer

The DB instance ran out of memory or CPU credits due to the intensive script

Answer

The max_connections parameter was set too low

Answer

The storage volume reached its maximum capacity

Question 16

A company is migrating a 2 TB Oracle database running on an on-premises Linux server to Amazon RDS for Oracle. The migration must have minimal downtime and must be fully reversible if any issues arise. The DBA has configured AWS DMS with a full load and ongoing replication task. The full load completes successfully, and CDC is replicating changes. During the cutover window, the DBA stops the source database and promotes the target RDS instance. However, after cutover, the application team reports that some recent transactions are missing from the target database. The DBA confirms that the DMS task showed a 'healthy' status before stopping. Which action should the DBA take to resolve the issue and prevent recurrence?

Accepted Answer

Before stopping the source database, run the 'Stop task' command with the '--apply-immediately' option to ensure all cached changes are written to the target.. In AWS DMS, after full load completes, ongoing replication (CDC) accumulates changes in a cache. To ensure no data loss during cutover, the DBA should stop the source database and then issue a 'Stop task' command with the '--apply-immediately' option (or use the 'Last Stop' job in the console) to flush all cached changes to the target before stopping the task. Option A (native export/import) would cause significant downtime and is unnecessary. Option B (increasing instance size) improves throughput but does not capture remaining cached changes. Option C (restarting from the beginning) would lose already migrated data and is not a targeted fix. Only option D directly addresses the issue of missing transactions by ensuring all CDC cached changes are applied before the task is stopped.

Answer

Rebuild the entire migration using a native Oracle export/import tool.

Answer

Increase the replication instance size to improve throughput.

Answer

Restart the DMS task from the beginning to recapture the missing data.

Question 17

A financial services company uses Amazon DynamoDB to store transaction data. The table is encrypted with an AWS managed KMS key. The compliance team requires that the encryption key be rotated every 90 days. The current key was created 6 months ago and has not been rotated. The company also needs to ensure that all access to the table is logged for audit purposes. The security engineer proposes to enable DynamoDB Streams and AWS CloudTrail. However, the compliance team notes that CloudTrail only logs management plane events (e.g., CreateTable) and not data plane events (e.g., GetItem, PutItem). What should the engineer do to meet both requirements?

Accepted Answer

Create a customer managed KMS key, enable automatic key rotation, and configure CloudTrail to log data events for the DynamoDB table.. To meet both requirements, the engineer should create a customer managed KMS key, enable automatic key rotation (which rotates the key annually, but for 90-day rotation, the engineer can create a new key every 90 days and update the table), and configure CloudTrail to log data events for the DynamoDB table. CloudTrail data events capture data plane operations like GetItem and PutItem, which addresses the logging requirement. Option A is incorrect because AWS managed keys do not support automatic rotation; also, CloudTrail data events are not tied to key type. Option B is incorrect because switching to a customer managed key alone does not enable data event logging. Option C is incorrect because DynamoDB Streams are used for change data capture and streaming to other services, not for audit logging of data plane operations; CloudWatch Logs from Streams do not capture all API calls.

Answer

Use AWS CloudTrail data events to capture DynamoDB data plane operations and store the logs in S3.

Answer

Switch to an AWS managed KMS key and enable automatic rotation.

Answer

Enable DynamoDB Streams and stream write events to CloudWatch Logs for auditing.

Question 18

A company runs an e-commerce platform using Amazon DynamoDB as the database. The table has a provisioned capacity of 5000 WCU and 3000 RCU. During a flash sale, the write traffic spikes to 8000 WCU for 10 minutes, causing significant throttling. The operations team notices that the table's WriteCapacityUnits metric shows 5000, but the ConsumedWriteCapacityUnits metric peaks at 4500. The application is experiencing errors and slow response times. The team wants to handle such spikes automatically without manual intervention and without over-provisioning. Which solution should be implemented?

Accepted Answer

Enable DynamoDB Auto Scaling with a target utilization of 70% and a minimum capacity of 5000 WCU. DynamoDB Auto Scaling can adjust capacity based on demand, and setting a target utilization of 70% allows headroom for spikes. Option B is wrong because increasing provisioned WCU to 8000 permanently would be costly and result in over-provisioning during normal traffic. Option C is wrong because while SQS can buffer requests, it adds latency and does not solve the real-time throttling issue; it changes the architecture to async processing, which may not be acceptable for an e-commerce platform. Option D is wrong because switching to on-demand capacity mode would handle the spikes automatically but can be significantly more expensive for a workload with a predictable baseline, and the team wants to avoid over-provisioning costs.

Answer

Increase the provisioned WCU to 8000 permanently

Answer

Implement an Amazon SQS queue to buffer write requests and process them asynchronously

Answer

Switch the table to on-demand capacity mode

Question 19

A small business runs a web application on a single Amazon RDS for MySQL DB instance. The application uses a master user account for all database operations. The security team is concerned about the risk of SQL injection and wants to implement the principle of least privilege. They want to create separate database users for read-only and read-write operations. The application currently uses a single connection string. The developer needs to modify the application to use two separate users. What is the correct approach to implement this securely?

Accepted Answer

Create a read-only user and a read-write user in the database, grant minimal privileges, and modify the application to use the appropriate user for each operation.. Creating separate users with minimal privileges and modifying the application to use the appropriate user for each operation reduces the risk of SQL injection and enforces least privilege. Option A is wrong because using stored procedures with a single master user does not eliminate the need for separate users for different privilege levels. Option B is wrong because restricting IP address does not address the need for granular permissions. Option C is wrong because enabling IAM database authentication with a single IAM role does not provide separate read-only and read-write capabilities.

Answer

Use stored procedures for all database operations and grant execute only to the master user.

Answer

Keep using the master user but restrict its IP address.

Answer

Enable IAM database authentication and use a single IAM role.

Question 20

A company runs a self-managed Redis cluster on Amazon EC2 for caching. The cluster has one primary and two replicas, each on c5.large instances. The application experiences high latency during peak hours. CloudWatch metrics show that the primary node's CPU utilization is consistently above 80% and the network bandwidth is near the instance limit. The replicas show moderate CPU usage. The team wants to reduce latency without increasing cost significantly. Which combination of actions should the team take? (Choose two.)

Accepted Answer

Enable Redis Cluster Mode and distribute data across multiple shards.. Enables Redis Cluster Mode to shard data across multiple nodes, reducing CPU and network load on the primary. Option E migrates to Amazon ElastiCache for Redis with Cluster Mode, which manages scaling and reduces operational overhead. Together, they address the bottleneck without significant cost increase. Option C (read from replicas) does not reduce primary write/CPU load. Option D (upgrade instance) increases cost and may still hit network limits. Option B (add replicas) increases cost and does not reduce primary load.

Answer

Add more EC2 instances as additional replicas to offload reads.

Answer

Configure the application to read from replica nodes.

Answer

Upgrade the primary to a c5.2xlarge instance type.