DBS-C01 Mock Exam 91 — 25 Questions

Question 1

A company is migrating an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 2 TB and has a sustained write rate of 150 MB/s. The migration must have minimal downtime. Which AWS service or tool should be used for the initial data load and ongoing replication?

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

Accepted Answer

Use AWS Database Migration Service (AWS DMS) with full load and ongoing replication. AWS DMS is the correct choice because it supports both a full load of the existing 2 TB database and ongoing change data capture (CDC) to replicate transactions with minimal downtime. DMS can handle sustained write rates of 150 MB/s by using appropriate instance sizing and tuning, and it provides built-in mechanisms for resumable loads and validation, which are critical for a large-scale migration with minimal downtime.

Answer

Use pg_dump and pg_restore

Answer

Use AWS Schema Conversion Tool (AWS SCT) to convert schema and AWS DMS for data migration

Answer

Use AWS S3 Transfer Acceleration to upload data to Amazon S3, then restore to RDS

Question 2

A database administrator notices that the CPU utilization on an Amazon RDS for PostgreSQL instance is consistently above 90% during peak hours. Which CloudWatch metric should be checked first to identify the cause of the high CPU usage?

Accepted Answer

DatabaseConnections. A high number of database connections can lead to increased CPU usage as each connection requires processing. Option B is wrong because NetworkThroughput measures network traffic, which is not a primary cause of high CPU. Option C is wrong because SwapUsage indicates memory pressure, not CPU. Option D is wrong because ReadIOPS measures disk I/O and may not directly cause high CPU.

Answer

NetworkThroughput

Answer

SwapUsage

Answer

ReadIOPS

Question 3

A company is deploying a global application that requires a database with sub-millisecond read latency across multiple regions. Which AWS database service should they use?

Accepted Answer

Amazon DynamoDB Global Tables. Amazon DynamoDB Global Tables provides a fully managed, multi-Region, multi-active database that delivers single-digit millisecond read and write latency anywhere in the world. It replicates data across AWS Regions automatically, ensuring sub-millisecond read latency by serving reads from the local Region. This makes it the ideal choice for a global application requiring low-latency reads across multiple regions.

Answer

Amazon ElastiCache for Redis

Answer

Amazon Aurora Global Database

Answer

Amazon RDS for MySQL with cross-region Read Replicas

Question 4

A company uses Amazon DynamoDB for a time-series IoT application. Each device sends a data point every second. The application queries data by device ID and timestamp range. Which table design is most efficient?

Accepted Answer

Use device ID as the partition key and timestamp as the sort key.. It models the access pattern directly: using device ID as the partition key ensures all data for a device is co-located, and timestamp as the sort key enables efficient range queries (e.g., Query with KeyConditionExpression on timestamp between start and end). This design avoids hot partitions and allows DynamoDB to retrieve the exact time-series slice without scanning.

Answer

Use a composite key of device ID and timestamp as the partition key.

Answer

Use device ID as the partition key and a random suffix as the sort key.

Answer

Use timestamp as the partition key and device ID as the sort key.

Question 5

Refer to the exhibit. A company is migrating an on-premises database to Amazon RDS for MySQL. During a test migration, the DMS task fails with the error shown. The source database is 500 GB and the target RDS instance has 500 GB allocated storage. What should be done to resolve this error and complete the migration?

Accepted Answer

Enable storage autoscaling on the RDS instance. The error indicates that the target RDS instance ran out of storage during the migration. Enabling storage autoscaling allows RDS to automatically increase storage when free space is low, preventing the migration from failing due to insufficient disk space. This is the correct resolution because the source database is 500 GB and the target has exactly 500 GB allocated, leaving no room for temporary data or logs during the migration.

Answer

Increase the DB instance class to a larger size

Answer

Increase the DMS task's allocated storage

Answer

Reduce the size of the source database

Question 6

A company is migrating a self-managed PostgreSQL database with extensions (PostGIS, pg_stat_statements) to Amazon RDS for PostgreSQL. After migration, they find that the extensions are not available. What is the most likely cause?

Accepted Answer

The required extensions are not included in the default parameter group and must be manually added to shared_preload_libraries.. Amazon RDS for PostgreSQL does not automatically load extensions that require shared library preloading, such as pg_stat_statements. These extensions must be explicitly added to the `shared_preload_libraries` parameter in the DB parameter group. PostGIS, while not requiring preloading, must be created via `CREATE EXTENSION` after the extension files are present; however, the most likely cause of extensions not being available is that the custom parameter group was not configured to include the required libraries in `shared_preload_libraries`.

Answer

The extensions are incompatible with the RDS engine version.

Answer

The RDS instance is not configured to allow extensions.

Answer

RDS does not support any PostgreSQL extensions.

Question 7

A company is running a production Amazon RDS for PostgreSQL database. The database experiences high write latency during peak hours. The company wants to reduce latency without changing the application code. Which solution is MOST cost-effective and scalable?

Accepted Answer

Increase the instance size to a larger DB instance class. Increasing the instance size to a larger DB instance class directly addresses high write latency by providing more CPU and memory resources, which improves the database's ability to process write operations faster. This is the most cost-effective and scalable solution because it does not require application code changes and can be scaled vertically as needed, whereas other options either do not reduce write latency or introduce unnecessary complexity.

Answer

Change the storage type to Provisioned IOPS (io1)

Answer

Enable RDS Proxy to pool database connections

Answer

Add a Multi-AZ standby to offload writes

Question 8

Arrange the steps to create an Amazon DynamoDB global table (multi-Region) in the correct order.

Accepted Answer

Create a DynamoDB table, then enable DynamoDB Streams, then add a replica table in another Region, then verify replication.. Global tables require streams enabled, then adding replicas in other Regions for multi-Region replication.

Answer

Create a DynamoDB table, then add a replica table in another Region, then enable DynamoDB Streams, then verify replication.

Answer

Enable DynamoDB Streams, then create a DynamoDB table, then add a replica table in another Region, then verify replication.

Answer

Add a replica table in another Region, then create a DynamoDB table, then enable DynamoDB Streams, then verify replication.

Question 9

A company wants to test an application against an Amazon RDS for MySQL database with a recent set of production data without impacting the production database. The test database must be available quickly and be refreshed regularly. Which solution should be used?

Accepted Answer

Create a read replica of the production database, then promote it to a standalone instance for testing.. Creating a read replica of the production RDS for MySQL database and then promoting it to a standalone instance is the fastest way to obtain a near-current copy of production data without impacting the source. The replica is created asynchronously using MySQL's native binlog replication, and promotion breaks the replication link, leaving a fully writable test instance. This approach minimizes setup time because the replica is already hydrated with data from the moment of creation.

Answer

Export production data to S3 and import into a test instance using Lambda.

Answer

Use AWS DMS to continuously replicate data from production to a test RDS instance.

Answer

Create a snapshot of the production database and restore it as a new RDS instance.

Question 10

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database contains sensitive personally identifiable information (PII). The security team requires that the data be encrypted in transit between the application and the RDS instance, and also encrypted at rest using a key managed by the company. Which THREE actions should the company take? (Choose THREE.)

Accepted Answer

Configure the RDS instance to require SSL/TLS connections.. Options A, C, and E are correct. Option A: Configuring the RDS instance to require SSL/TLS encrypts data in transit, meeting the encryption-in-transit requirement. Option C: Enabling encryption at rest for the RDS instance at launch time allows use of AWS KMS for encryption, satisfying the at-rest encryption requirement. Option E: Creating a customer managed key (CMK) in AWS KMS enables the company to manage the encryption key, meeting the requirement for a key managed by the company. Option B is incorrect because setting rds.force_ssl to 1 in the DB parameter group is a step within configuring SSL/TLS, but the primary action is option A; moreover, the correct method to enforce SSL for Oracle RDS involves using the option group with the SSL option, not just the parameter group. Option D is incorrect because Transparent Data Encryption (TDE) using CloudHSM is not required; the at-rest encryption requirement is already fulfilled by enabling RDS encryption with a CMK (options C and E), and TDE with CloudHSM adds unnecessary complexity and potential licensing issues.

Answer

Modify the DB parameter group to set the 'rds.force_ssl' parameter to 1.

Answer

Enable Transparent Data Encryption (TDE) using CloudHSM.

Question 11

A company is migrating a 3 TB PostgreSQL database from on-premises to Amazon Aurora PostgreSQL. They need to minimize downtime and ensure that the migration is completed within a maintenance window. Which approach should they use?

Accepted Answer

Use AWS DMS with full load and ongoing replication (CDC). AWS DMS with full load and ongoing replication (CDC) is the correct approach because it allows you to perform an initial full load of the 3 TB database while continuously capturing changes from the source PostgreSQL using logical replication (via the pglogical extension or native slot-based replication). This minimizes downtime by keeping the target Aurora PostgreSQL nearly synchronized, and you can switch over during a maintenance window with only a brief outage to apply any final lag.

Answer

Use AWS SCT to convert the schema and then migrate data

Answer

Use pg_dump to export the database and pg_restore to import into Aurora

Answer

Take a file system snapshot and restore to Aurora

Question 12

A company runs an Amazon Aurora MySQL database. The database experiences a sudden spike in connections and then becomes unresponsive. The DB instance has a db.r5.large class with 8 GB memory. The maximum connections parameter is set to the default. Which is the most likely cause of the unresponsiveness?

Accepted Answer

The number of connections exceeded the max_connections limit. The default max_connections for Aurora MySQL is based on memory, and with 8 GB, it is about 800. A spike exceeding that can exhaust resources. Option A is wrong because storage auto-scaling is seamless. Option B is wrong because burst balance applies to gp2 volumes, but Aurora uses cluster storage. Option D is wrong because replica lag would affect reads, not make the instance unresponsive.

Answer

The DB instance's EBS burst balance dropped to zero

Answer

The storage volume ran out of allocated space

Answer

A read replica had high replication lag

Question 13

A company uses Amazon RDS for MySQL and wants to ensure that database users are authenticated using IAM database authentication. Which action must be performed to enable this?

Accepted Answer

Set the parameter 'require_secure_transport' to ON and use the AWSAuthenticationPlugin.. IAM database authentication requires a specific parameter group setting (require_secure_transport=ON) and authentication plugin. Option A is wrong because native MySQL authentication is not IAM. Option B is wrong because IAM roles for RDS are for API access, not database authentication. Option C is wrong because the standard MySQL port is 3306.

Answer

Create database users with MySQL native password authentication.

Answer

Attach an IAM role to the RDS instance for database authentication.

Answer

Change the database port to 3306 to enable IAM authentication.

Question 14

A company is migrating a MySQL database to Amazon RDS for MySQL. They want to use AWS DMS for continuous replication. Which TWO prerequisites must be met before starting the migration?

Accepted Answer

Enable binary logging (binlog) on the source MySQL database.. AWS DMS uses MySQL's binary log (binlog) to capture ongoing changes for continuous replication (CDC). Enabling binlog on the source database is mandatory because DMS reads the binlog to identify insert, update, and delete operations after the initial full load. Without binlog enabled, DMS cannot perform change data capture and the migration will be limited to a one-time full load only.

Answer

Set the source database to read-only mode during migration.

Answer

Place the source database in a VPC.

Answer

Create an S3 bucket to store the migration logs.

Question 15

An e-commerce company runs a multi-AZ deployment of Amazon RDS for MySQL. During a recent failover test, the application experienced a 30-second write outage. The application uses a connection pooling library. The DB instance has a 60-second TTL for DNS records. What is the MOST likely cause of the outage?

Accepted Answer

The connection pool had open connections to the old primary, and DNS TTL caused a delay in reconnecting to the new primary.. During a Multi-AZ failover, the RDS DNS record is automatically updated to point to the new primary. However, the application's connection pool may still have open connections to the old primary IP. Because the DNS TTL is 60 seconds, the client may continue to resolve to the old (cached) IP for up to 60 seconds, causing a write outage until connections are re-established to the new primary. Option B is incorrect because a cold start typically refers to an application starting from scratch, which is not the case here. Option C is incorrect because the DNS record is indeed updated after failover; the issue is client-side caching. Option D is incorrect because Multi-AZ failover usually completes within 1-2 minutes, but the outage duration is determined by DNS TTL and connection pooling behavior, not the failover time itself.

Answer

The application experienced a cold start after the failover.

Answer

The DNS record for the RDS endpoint was not updated after the failover.

Answer

The Multi-AZ failover took longer than 30 seconds to complete.

Question 16

A company is migrating a 2 TB Oracle database from on-premises to Amazon RDS for Oracle. The network bandwidth is 100 Mbps. The migration must be completed within 3 days. Which approach is MOST efficient?

Accepted Answer

Use AWS DMS with parallel load and ongoing replication.. AWS DMS with parallel load and ongoing replication is the most efficient approach because it can handle the 2 TB migration within the 3-day window over a 100 Mbps link. At 100 Mbps, the theoretical maximum transfer is about 1.08 TB per day (100 Mbps * 86400 seconds / 8 bits per byte / 1024^4), so 2 TB would take nearly 2 days just for the full load. DMS's parallel load splits the data into multiple tasks, maximizing throughput and reducing the full-load time, while ongoing replication captures changes during the migration, allowing a seamless cutover without downtime.

Answer

Use Oracle RMAN to create a backup and restore to RDS.

Answer

Use Oracle Data Pump with a single export and import.

Answer

Use Oracle GoldenGate for real-time replication.

Question 17

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 1 TB and has a large number of stored procedures and triggers. The migration must minimize application changes. Which migration approach should be used?

Accepted Answer

Use AWS Database Migration Service (AWS DMS) with full load and ongoing replication. AWS DMS with full load and ongoing replication minimizes application changes by supporting heterogeneous migrations with minimal downtime, and it can handle stored procedures and triggers by replicating data changes in near real-time without requiring schema conversion. AWS DMS directly supports Oracle as a source and Amazon RDS for Oracle as a target, preserving the existing schema and procedural logic, which avoids the need for application rewrites.

Answer

Use AWS Schema Conversion Tool (AWS SCT) to convert the schema and AWS DMS for data migration

Answer

Use Oracle Data Pump (expdp/impdp) to export and import the database

Answer

Use AWS S3 to store the data and AWS Glue to transform and load into RDS

Question 18

Arrange the steps to enable encryption at rest for an existing unencrypted Amazon RDS for MariaDB DB instance in the correct order.

Accepted Answer

Create a manual snapshot, then copy the snapshot with encryption enabled, then restore the encrypted snapshot to a new DB instance, then migrate applications.. Encryption at rest for an existing instance requires creating an encrypted snapshot and restoring it, then migrating applications.

Answer

Create a manual snapshot, then restore the snapshot to a new instance, then copy the new instance with encryption, then migrate applications.

Answer

Create a manual snapshot, then copy the snapshot with encryption, then modify the original DB instance to use encryption.

Answer

Enable encryption on the original DB instance via a maintenance window, then take a snapshot, then restore.

Question 19

A gaming company runs a global leaderboard on Amazon DynamoDB. The leaderboard is updated frequently and must return the top 100 scores in milliseconds. The current design uses a single table with a Global Secondary Index (GSI) on score. However, the query to retrieve top scores often throttles under load. Which design change would best improve performance?

Accepted Answer

Implement a write shard pattern using a random suffix on the partition key and a GSI on score.. The write shard pattern distributes high-frequency writes across multiple partition keys by appending a random suffix, preventing hot partitions. The GSI on score still allows efficient top-N queries by scanning the index in descending order. This avoids throttling by spreading write capacity evenly, while the GSI remains a sparse index that can be queried without impacting the base table's write throughput.

Answer

Use a scan operation with a filter to retrieve top scores.

Answer

Add DynamoDB Accelerator (DAX) in front of the table.

Answer

Switch to strongly consistent reads for the leaderboard query.

Question 20

A company is migrating a 500 GB Oracle database to Amazon Aurora PostgreSQL. They need to convert the schema and migrate the data with minimal downtime. Which THREE actions should they take? (Choose three.)

Accepted Answer

Use AWS Schema Conversion Tool (SCT) to assess and convert Oracle-specific features like hierarchical queries.. AWS Schema Conversion Tool (SCT) is the correct tool for assessing and converting Oracle-specific features like hierarchical queries (e.g., CONNECT BY) into PostgreSQL-compatible syntax (e.g., recursive CTEs). This is essential for schema migration to Aurora PostgreSQL, and SCT provides a detailed assessment report to identify and automate conversion of such features.

Answer

Modify the application to use Aurora PostgreSQL-specific SQL syntax before migration.

Answer

Use AWS Snowball Edge to transfer the data to AWS and then load into Aurora.