DBS-C01 Practice Exam 66 — 20 Questions

Question 1

Refer to the exhibit. A database specialist is investigating an application outage that occurred at 14:25 UTC. The RDS event log shows the events above. What is the most likely cause of the outage?

Accepted Answer

A Multi-AZ failover occurred at 14:25 UTC, causing a brief outage.. The RDS event log shows 'Multi-AZ failover completed' at 14:25 UTC, which would cause a brief outage during the DNS switchover. The subsequent restart at 14:30 UTC is likely a result of the failover (e.g., instance recovery). Option A is wrong because there is no event indicating a maintenance window. Option B is wrong because storage-full events would show before the outage, not a failover event. Option D is wrong because a manual reboot would not show a Multi-AZ failover event; the restart at 14:30 is after the failover.

Answer

A maintenance window update was applied, causing the instance to become unavailable.

Answer

The DB instance ran out of storage and became read-only.

Answer

The DB instance restarted at 14:30 UTC due to a manual reboot.

Question 2

A logistics company uses Amazon RDS for MySQL to track package shipments. The 'shipments' table contains 200 million rows and has a primary key on 'shipment_id' (UUID). The application frequently queries for shipments by 'tracking_number', which is a unique string of 20 characters. The DBA created a B-tree index on tracking_number. The queries by tracking_number are fast, but inserts are becoming slower over time. The table has 50 GB of data. The company plans to double the insert rate next month. The database is a db.r5.large instance with 500 GB of Provisioned IOPS SSD storage. The instance's CPU utilization is below 30%, and there is no lock contention. What should the database specialist do to improve insert performance?

Accepted Answer

Change the primary key from UUID to an auto-increment integer, and keep the tracking_number index.. UUID primary keys cause random writes and index fragmentation, degrading insert performance as the table grows. Switching to an auto-increment integer primary key allows sequential writes to the clustered index, reducing page splits and improving insert throughput. The B-tree index on tracking_number remains to support fast queries, while the new primary key eliminates the UUID write overhead.

Answer

Add a read replica and route insert queries to the replica.

Answer

Drop the index on tracking_number to reduce write overhead.

Answer

Increase the provisioned IOPS to 20,000.

Question 3

A company is planning to migrate a 5 TB Oracle data warehouse to Amazon Redshift. The migration must be completed within a 2-day maintenance window. The source database is heavily normalized and uses complex joins. Which strategy is most appropriate?

Accepted Answer

Use AWS SCT to convert the Oracle schema to Redshift-compatible format, then use AWS DMS to load the data.. AWS Schema Conversion Tool (SCT) is specifically designed to convert Oracle schemas (including heavily normalized structures with complex joins) into Amazon Redshift-compatible format, which is essential for a data warehouse migration. AWS DMS then efficiently loads the converted schema and data into Redshift within the 2-day window, as it can handle large volumes with full load and ongoing replication if needed.

Answer

Use AWS DMS to directly migrate data to Redshift with full load and ongoing replication.

Answer

Export data to flat files, use S3 Transfer Acceleration to upload to S3, then COPY into Redshift.

Answer

Use AWS Glue to crawl the Oracle schema and create Redshift tables, then run a Glue ETL job to load data.

Question 4

A company has an Amazon DynamoDB table with auto scaling enabled. During a traffic spike, the application experiences high write latencies. Which action should the company take to troubleshoot the latency issue?

Accepted Answer

Monitor the ThrottledWriteEvents metric in CloudWatch.. ThrottledWriteEvents metric indicates write requests that were throttled due to exceeding provisioned capacity. If this metric spikes during traffic spikes, it suggests that auto scaling is not scaling fast enough, leading to high write latencies. Option B is incorrect because switching to on-demand is a remediation, not a troubleshooting step; it does not help identify the root cause. Option C is incorrect because disabling auto scaling and manually increasing capacity might solve the issue temporarily but is not a troubleshooting approach; it bypasses auto scaling logic. Option D is incorrect because read capacity does not affect write latencies.

Answer

Switch the table to on-demand capacity mode.

Answer

Disable auto scaling and manually increase write capacity.

Answer

Increase the read capacity of the table.

Question 5

A social media application uses Amazon DynamoDB as its primary data store. The application stores user posts and allows users to retrieve the most recent 10 posts of users they follow. The access pattern is a followee-based query that needs to be highly scalable and low-latency. Which DynamoDB table design should the database specialist recommend?

Accepted Answer

Use a composite primary key with a partition key of follower ID and a sort key of timestamp, and store the followee ID as an attribute. It models the access pattern directly: the follower ID as the partition key ensures all posts from followed users are co-located, and the sort key of timestamp allows efficient retrieval of the most recent 10 posts via a Query with a limit of 10 and descending order. This design avoids expensive scans or secondary index lookups, meeting the low-latency and scalability requirements.

Answer

Use a partition key of post ID and a local secondary index on the followee ID

Answer

Use a single table with a scan operation and filter on the followee attribute

Answer

Design the table with a partition key of user ID and a sort key of timestamp, and create a global secondary index (GSI) on followee ID

Question 6

A company is designing a database for an e-commerce application that requires high availability and automatic failover. The application performs mainly read-heavy workloads with occasional write spikes during flash sales. Which AWS database service is most suitable for this workload?

Accepted Answer

Amazon Aurora MySQL. Amazon Aurora MySQL is the most suitable choice because it is designed for high availability with automatic failover (typically under 30 seconds) and provides up to 15 low-latency read replicas that can handle read-heavy workloads. During write spikes like flash sales, Aurora's distributed storage subsystem automatically scales I/O capacity without manual intervention, and its Multi-AZ deployment ensures continuous availability even if the primary instance fails.

Answer

Amazon DynamoDB with global tables

Answer

Amazon ElastiCache for Redis

Answer

Amazon RDS for MySQL with Multi-AZ

Question 7

A company is migrating a 2 TB PostgreSQL database from on-premises to Amazon RDS for PostgreSQL. The database has a 4-hour downtime window. The company requires minimal data loss and wants to use AWS DMS. The on-premises network has a 100 Mbps internet connection. Which migration method should the company use?

Accepted Answer

Use AWS DMS with a full load and ongoing change data capture (CDC) replication.. AWS DMS with a full load and ongoing change data capture (CDC) replication allows the company to migrate the 2 TB database with minimal data loss within the 4-hour downtime window. The full load transfers the existing data, and CDC captures and applies ongoing changes from the source database to the target RDS instance, reducing the final cutover downtime to seconds or minutes. This approach is ideal for large databases with tight downtime constraints and limited bandwidth (100 Mbps), as the initial full load can run before the downtime window, and only the final CDC catch-up occurs during the window.

Answer

Use AWS Schema Conversion Tool (SCT) to migrate the data to Amazon RDS.

Answer

Use AWS DMS with a full load only, then stop the source database and resume applications.

Answer

Use pg_dump and pg_restore to export and import the database during the downtime window.

Question 8

A company's RDS for SQL Server instance has been running for 3 years. The DBA notices that the DB instance's allocated storage (500 GB) is 80% full. The application is write-heavy. The DBA needs to increase storage without downtime. What is the most efficient way to achieve this?

Accepted Answer

Use the Modify DB Instance API to increase allocated storage.. RDS for SQL Server supports modifying storage online using the Modify DB Instance API without downtime. Option A is incorrect because you cannot attach additional EBS volumes directly to an RDS instance; RDS manages its own storage. Option B is incorrect because creating a new instance and migrating data would require downtime. Option C is incorrect because taking a snapshot and restoring a new instance also incurs downtime and is less efficient than modifying storage in place.

Answer

Attach an additional EBS volume to the DB instance.

Answer

Create a new DB instance with larger storage and migrate data.

Answer

Take a snapshot and restore a new instance with larger storage.

Question 9

A company is migrating a 200 GB PostgreSQL database to Amazon Aurora PostgreSQL. They want to use the AWS DMS console to create a migration task. The source database is in a VPC and the target Aurora cluster is in the same VPC. The DMS replication instance is also in the same VPC. The source database is publicly accessible. What additional configuration is required to enable connectivity between DMS and the source database?

Accepted Answer

Configure the source database's security group to allow inbound traffic from the DMS replication instance's security group.. The source database is publicly accessible but resides in a VPC, and the DMS replication instance is in the same VPC. To allow the DMS replication instance to connect to the source database, the source database's security group must have an inbound rule that permits traffic on the database port (e.g., 5432 for PostgreSQL) from the DMS replication instance's security group. This ensures that only the replication instance can initiate the connection, maintaining security within the VPC.

Answer

Associate the DMS replication instance with a subnet group that includes public subnets.

Answer

Place the source database in the same public subnet as the DMS replication instance.

Answer

Create a VPC endpoint for the source database service.

Question 10

A company is designing a database for a global e-commerce platform that requires low-latency reads and writes across multiple AWS Regions. The database must support strongly consistent reads and provide automatic failover. Which AWS service should the company use?

Accepted Answer

Amazon DynamoDB global tables. Amazon DynamoDB global tables provide a fully managed, multi-Region, multi-active database solution that delivers low-latency reads and writes across AWS Regions. It supports strongly consistent reads when using the same-Region endpoint and offers automatic failover by allowing any Region to handle writes independently, ensuring high availability without manual intervention.

Answer

Amazon ElastiCache for Redis global datastore

Answer

Amazon S3 with cross-region replication

Answer

Amazon Aurora Global Database

Question 11

A company is migrating an on-premises Microsoft SQL Server database to Amazon RDS for SQL Server. The database uses SQL Server Agent jobs, custom CLR assemblies, and cross-database queries. Which of the following will require modification before migration?

Accepted Answer

SQL Server Agent jobs. SQL Server Agent jobs are not supported in Amazon RDS for SQL Server because RDS is a managed service that does not provide access to the underlying operating system or the SQL Server Agent service. To migrate job scheduling, you must use alternatives such as AWS Database Migration Service (DMS) tasks, AWS Lambda, or Amazon RDS for SQL Server native scheduling via stored procedures and Windows Task Scheduler on an EC2 instance.

Answer

Cross-database queries

Answer

Custom CLR assemblies

Answer

Stored procedures that use dynamic SQL

Question 12

A database administrator is monitoring Amazon RDS for PostgreSQL using CloudWatch. The DB instance shows high CPU utilization, but the number of connections is normal. What is the most likely cause of the high CPU utilization?

Accepted Answer

There are long-running queries or missing indexes causing high CPU usage.. High CPU utilization with a normal number of connections often indicates inefficient queries or missing indexes, which cause full table scans and excessive CPU usage. Option A is incorrect because gp2 burst balance affects storage performance, not CPU. Option B is incorrect because memory pressure and swapping typically cause high I/O wait times, not sustained high CPU. Option D is incorrect because Read Replicas offload read traffic, they do not cause high CPU on the primary instance.

Answer

The DB instance has a low burst balance for gp2 storage.

Answer

The instance is low on memory and is swapping.

Answer

The DB instance has a large number of Read Replicas.

Question 13

A company is using Amazon DynamoDB with a global table in two regions. The application is experiencing high write latency on the replica table in the secondary region. Which THREE factors could contribute to this issue?

Accepted Answer

Large item sizes being written to the table.. Global tables replicate writes asynchronously. Large item sizes (A) increase the time to process each write. Network latency (B) between regions affects the replication time. Insufficient write capacity (E) on the replica table can cause throttling and increased latency. Auto scaling configuration (C) is not a direct cause; it helps manage capacity. Read capacity (D) does not affect write latency.

Answer

Auto scaling configuration on the replica table.

Answer

Low read capacity on the replica table.

Question 14

Refer to the exhibit. A database engineer runs the query above to troubleshoot an application error. The query returns no results even though the database is generating errors. What is the most likely reason?

Accepted Answer

The log stream format uses a different field name for the error message. The query filters on the 'message' field, but the log stream format may use a different field name for the error message, such as 'errorMessage' or 'event.message'. Since the query returns no results despite errors existing, the most likely reason is a field name mismatch. Option B is incorrect because the query uses a regex pattern with case-insensitive matching (indicated by the 'i' flag), so case sensitivity is not an issue. Option C is incorrect because queries in CloudWatch Logs Insights default to the last 15 minutes if no time range is specified, so that would not cause zero results if errors are recent. Option D is incorrect because exporting to CloudWatch Logs is not required for querying; the logs are already in CloudWatch Logs.

Answer

The regex pattern does not match because it is case-sensitive

Answer

The query does not specify a time range, so no results are returned

Answer

The log group has not been configured to export to CloudWatch Logs

Question 15

Which THREE actions should be taken to troubleshoot an Amazon RDS for PostgreSQL instance that is unresponsive? (Choose 3.)

Accepted Answer

Verify that the security group allows inbound traffic on the database port. To troubleshoot an unresponsive Amazon RDS for PostgreSQL instance, the standard initial steps are: C) Verify that the security group allows inbound traffic on the database port – connectivity issues are a common cause of unresponsiveness. D) Check the database error logs in CloudWatch Logs – logs may reveal database-specific errors like out-of-memory or corruption. E) Review CloudWatch metrics for CPU, memory, and disk I/O – high utilization can indicate resource exhaustion. Option A (reboot immediately) is wrong because it may destroy diagnostic evidence. Option B (modify instance class) is premature without first assessing the problem.

Answer

Reboot the DB instance immediately

Answer

Modify the DB instance to a larger instance class

Question 16

A company is using Amazon DynamoDB with auto scaling enabled. The application is experiencing higher than expected write throttling. Which action should be taken to resolve this issue?

Accepted Answer

Increase the minimum provisioned capacity for the table.. Auto scaling adjusts capacity based on workload, but it can lag behind sudden traffic spikes, causing write throttling. Increasing the minimum provisioned capacity ensures a baseline capacity that can accommodate predictable bursts, reducing throttling. Option A (increase min capacity) is correct. Option B (disable auto scaling and set fixed capacity) would remove the benefit of dynamic scaling and may not handle varying loads. Option C (decrease max capacity) would limit the table's ability to scale up, potentially worsening throttling. Option D (switch to on-demand) could eliminate throttling but at higher cost, and the question asks for a resolution while keeping auto scaling enabled.

Answer

Disable auto scaling and set a fixed provisioned capacity.

Answer

Decrease the maximum provisioned capacity to limit writes.

Answer

Switch the table to on-demand capacity mode.

Question 17

A company is using Amazon Redshift for data warehousing. They need to ensure that data is encrypted at rest using a customer-managed AWS KMS key. The cluster is currently unencrypted. What is the simplest way to enable encryption?

Accepted Answer

Create a new Redshift cluster with encryption enabled and migrate the data.. You cannot enable encryption on an existing Amazon Redshift cluster. The simplest approach is to create a new cluster with encryption enabled using a customer-managed AWS KMS key, then migrate the data from the old cluster to the new one using tools such as UNLOAD/COPY or AWS DMS. Option C (snapshot and restore) is also valid, but it is not the simplest because it requires creating a snapshot and then restoring it to a new encrypted cluster, which involves extra steps. Therefore, option A is correct.

Answer

Enable encryption directly on the existing cluster using AWS CLI.

Answer

Create a snapshot of the existing cluster and restore it to a new encrypted cluster.

Answer

Modify the existing cluster and enable encryption using the Redshift console.

Question 18

A company has a 100 GB MySQL database on an EC2 instance. They want to migrate to Amazon RDS for MySQL with minimal downtime. They have set up replication from the source to the target using MySQL native replication. After enabling replication, the 'Seconds_Behind_Master' value is increasing. The source database is write-heavy. What should the team do to reduce replication lag?

Accepted Answer

Increase the RDS instance size to a larger instance class.. The replication lag is increasing because the RDS instance is not powerful enough to apply changes from the write-heavy source as fast as they arrive. Increasing the RDS instance class (option C) provides more CPU and memory resources, allowing the replica to apply transactions more quickly and reduce lag. Option A (tuning the source) might help but is not the most direct solution if the target is the bottleneck. Option B (Multi-AZ) improves availability, not replication performance. Option D (AWS DMS) is an alternative migration tool but does not directly address lag in an existing native replication setup.

Answer

Tune the source database to reduce write load.

Answer

Enable Multi-AZ on the RDS instance.

Answer

Switch to AWS DMS for migration.

Question 19

A company is migrating a database using AWS DMS. The IAM policy shown is attached to the DMS replication instance role. When the DMS replication task is created in the us-west-2 region, it fails. What is the most likely cause?

Accepted Answer

The IAM policy restricts the region to us-east-1, but the task is created in us-west-2.. The IAM policy explicitly restricts the region to us-east-1 using the `aws:RequestedRegion` condition key. When the DMS replication task is created in us-west-2, the policy denies the `dms:CreateReplicationTask` action because the region condition fails, causing the task creation to fail. DMS replication tasks require the IAM role to have permissions in the same region where the task is being created.

Answer

The IAM policy does not allow the 'dms:CreateReplicationTask' action.

Answer

The IAM policy does not specify the VPC where the replication instance is deployed.

Answer

The IAM policy does not specify the resource ARN for the replication instance.

Question 20

A company wants to encrypt an existing unencrypted Amazon RDS for PostgreSQL DB instance. What is the correct procedure?

Accepted Answer

Take a snapshot of the instance, create an encrypted copy of the snapshot, and restore the encrypted snapshot to a new DB instance.. Encryption for an existing unencrypted Amazon RDS for PostgreSQL DB instance cannot be enabled directly. The correct procedure is to take a snapshot of the instance, create an encrypted copy of that snapshot, and then restore the encrypted snapshot to a new DB instance. Option A accurately describes this process. Option B is incorrect because restoring a snapshot does not allow enabling encryption during the restore; encryption must be applied at the time of snapshot copy. Option C is incorrect because you cannot modify a running DB instance to enable encryption. Option D is incorrect because creating a read replica does not encrypt the primary instance; encryption must be set up before replica creation.

Answer

Take a snapshot of the instance and restore it with encryption enabled.

Answer

Modify the DB instance and enable encryption in the RDS console.

Answer

Create a read replica of the instance and enable encryption on the replica.