DBS-C01 Mock Exam 90 — 25 Questions

Question 1

Refer to the exhibit. A DBA is monitoring a DMS migration task from on-premises Oracle to Amazon RDS for Oracle. The full load completed successfully with 50 tables. However, the DBA notices that the CDC phase has not started. What is the most likely reason?

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

Accepted Answer

The replication task was stopped after the full load completed. The most likely reason the CDC phase has not started is that the replication task was stopped after the full load completed. In AWS DMS, after the full load finishes, the task must remain in a running state to transition to the CDC phase. If the task is stopped, CDC cannot begin, and the DBA would need to resume or restart the task to capture ongoing changes.

Answer

The task was not configured with CDC enabled

Answer

The full load encountered errors on some tables

Answer

The source Oracle database is not generating redo logs

Question 2

A database specialist is troubleshooting an Amazon RDS for PostgreSQL instance that has high replication lag between the primary and a read replica. Which TWO metrics should the specialist review to identify the cause? (Select TWO.)

Accepted Answer

ReadIOPS on the replica. High ReadIOPS on the read replica can indicate heavy read activity, which may cause replication lag as the replica struggles to apply changes fast enough. Option D is correct because ReplicaLag directly measures the time delay between the primary and replica, confirming the presence of lag. Option A is incorrect because WriteIOPS on the primary reflects write workload, not lag cause. Option C is incorrect because DatabaseConnections do not directly affect replication lag. Option E is incorrect because NetworkThroughput is not a metric that directly indicates replication lag; it could be a factor but is not a standard RDS metric for diagnosing lag.

Answer

WriteIOPS on the primary

Answer

DatabaseConnections on the primary

Answer

NetworkThroughput between primary and replica

Question 3

A security engineer creates the IAM policy shown in the exhibit and attaches it to an IAM user. What is the effect of this policy?

Accepted Answer

The user can modify 'prod-db' but cannot delete it.. The IAM policy allows DescribeDBInstances and ModifyDBInstance on all resources, but explicitly denies DeleteDBInstance on the database 'prod-db'. Since an explicit deny overrides any allow, the user cannot delete 'prod-db'. However, the policy does not allow DeleteDBInstance on any database, so the user cannot delete any database. For 'prod-db', the user can still modify and describe it because the deny is only for the delete action. Thus, the user can modify 'prod-db' but cannot delete it.

Answer

The user can delete any database except 'prod-db'.

Answer

The user can describe all databases except 'prod-db'.

Answer

The user can modify any database except 'prod-db'.

Question 4

A company is designing a database for an e-commerce platform that needs to store product catalog data. The data is highly relational with many-to-many relationships between products, categories, and suppliers. The platform requires ACID transactions and complex joins. Which TWO AWS database solutions are suitable for this workload? (Choose TWO.)

Accepted Answer

Amazon Aurora MySQL. Amazon Aurora MySQL is a fully ACID-compliant relational database that supports complex joins and many-to-many relationships through foreign keys and junction tables. It is optimized for high-throughput e-commerce workloads with features like auto-scaling storage and up to 15 low-latency read replicas, making it suitable for product catalog data that requires transactional consistency.

Answer

Amazon ElastiCache for Redis

Answer

Amazon Neptune

Answer

Amazon DynamoDB

Question 5

A company uses Amazon DynamoDB with provisioned capacity. The application team reports occasional ProvisionedThroughputExceededException errors. The database administrator notices that the errors occur during periods of high traffic. What is the most cost-effective way to handle these errors without over-provisioning capacity?

Accepted Answer

Implement exponential backoff and retry logic in the application.. Implementing exponential backoff and retry logic allows the application to handle throttling errors gracefully by retrying requests after a delay, which is the most cost-effective solution as it avoids over-provisioning capacity. Option A is incorrect because increasing capacity to peak levels is costly and inefficient. Option B is incorrect because DAX is a caching layer that reduces read load but does not help with write throttling or prevent ProvisionedThroughputExceededException errors for writes. Option D is incorrect because switching to on-demand capacity mode can be more expensive for predictable traffic patterns, and the question asks for the most cost-effective approach without over-provisioning.

Answer

Increase the provisioned read and write capacity to the peak traffic level.

Answer

Use DynamoDB Accelerator (DAX) to cache frequently accessed items.

Answer

Switch to on-demand capacity mode.

Question 6

A company is designing a document management system using Amazon DocumentDB. Each document is up to 10 MB. The application needs to retrieve multiple documents by their IDs in a single request. The IDs are known at query time. Which query pattern is most efficient?

Accepted Answer

Use a find operation with the $in operator on the _id field.. The `$in` operator on the `_id` field allows DocumentDB to use the primary key index directly, retrieving multiple documents in a single round trip with minimal overhead. This is the most efficient pattern because it leverages the clustered index on `_id` and avoids the performance penalty of multiple queries or full scans.

Answer

Use a find operation with the $or operator on the _id field.

Answer

Use a scan operation with a filter on the _id field.

Answer

Issue multiple get operations in parallel.

Question 7

A startup needs a fully managed relational database with automated backups and scaling. They expect unpredictable workloads. Which AWS service meets these requirements?

Accepted Answer

Amazon Aurora Serverless. Amazon Aurora Serverless is a fully managed relational database that automatically scales capacity up or down based on application demand, making it ideal for unpredictable workloads. It also provides automated backups, continuous backups to Amazon S3, and point-in-time recovery, meeting all stated requirements.

Answer

Amazon DynamoDB

Answer

Amazon Redshift

Answer

Amazon ElastiCache

Question 8

A company is using Amazon DynamoDB to store customer session data. The security team requires that all data is encrypted at rest using a customer-managed KMS key, and that access to the key is restricted to specific IAM roles. The company also wants to ensure that DynamoDB Accelerator (DAX) cluster is encrypted. Which steps should be taken to meet these requirements?

Accepted Answer

Create the DynamoDB table with encryption using a customer-managed KMS key. Create the DAX cluster and enable encryption at rest using the same KMS key.. DynamoDB tables can be encrypted at rest with a customer-managed KMS key at creation, and DAX clusters also support encryption at rest using the same or a different KMS key, meeting the requirement. Option B is wrong because DynamoDB encryption cannot be enabled after table creation; it must be specified at creation. Option C is wrong because it uses default encryption (AWS managed key) for the table, not a customer-managed key. Option D is wrong because it refers to encryption in transit (TLS) for DAX, but the requirement is for encryption at rest; DAX encryption at rest is not addressed.

Answer

Create the DynamoDB table without encryption, then use the AWS CLI to enable encryption after creation.

Answer

Create the DynamoDB table with default encryption, and create the DAX cluster with a separate customer-managed KMS key.

Answer

Create the DynamoDB table with encryption using a customer-managed key, and enable encryption in transit on the DAX cluster using TLS.

Question 9

A company is using Amazon Aurora MySQL-Compatible Edition. The security team requires that all connections to the database use SSL/TLS. The application currently connects using a standard JDBC connection string without SSL. What changes are needed to enforce SSL connections?

Accepted Answer

Modify the DB cluster parameter group to set require_secure_transport to ON and update the application connection string to use SSL parameters.. To enforce SSL for all connections to an Amazon Aurora MySQL database, you must modify the DB cluster parameter group to set require_secure_transport to ON, which rejects non-SSL connections. Additionally, the application's JDBC connection string must be updated to include SSL parameters (e.g., useSSL=true) so that the application initiates an SSL connection. Option A is incomplete because modifying the parameter group alone does not enforce SSL on existing connections if the application does not use SSL. Option C is incorrect because security groups do not have an SSL flag; they control network access based on IP and port. Option D is incorrect because IAM roles do not enforce SSL encryption; they handle authentication and authorization.

Answer

Modify the DB cluster parameter group to set require_secure_transport to ON.

Answer

Modify the security group to only allow traffic on port 3306 with the SSL flag.

Answer

Create an IAM role that requires SSL for database access and assign it to the application.

Question 10

A gaming company uses Amazon DynamoDB as the database for user profiles and game state. The application requires strongly consistent reads for the user's own profile, but eventually consistent reads for leaderboard queries. How should the company design the table and queries?

Accepted Answer

Use the ConsistentRead parameter set to true for profile queries and false for leaderboard queries.. DynamoDB supports both strongly consistent reads and eventually consistent reads on the same table, controlled by the `ConsistentRead` parameter in the `GetItem`, `Query`, or `Scan` API calls. Setting `ConsistentRead=true` for profile queries ensures the most up-to-date data, while `ConsistentRead=false` (the default) for leaderboard queries provides lower latency and higher throughput, which is ideal for read-heavy, non-critical data. This design avoids the cost and complexity of multiple tables or additional services.

Answer

Create two separate tables: one for strong consistency and one for eventual consistency.

Answer

Enable DynamoDB Accelerator (DAX) for strong consistency on all reads.

Answer

Configure DynamoDB Streams to replicate data to a second table for strong consistency.

Question 11

A financial services company runs a critical PostgreSQL database on Amazon RDS. The database stores transaction records and requires point-in-time recovery (PITR) with a recovery window of 35 days. The database size is 500 GB and grows at 10 GB per day. The team wants to minimize storage costs while meeting the recovery SLA. Which backup strategy should they use?

Accepted Answer

Enable automated backups with a retention period of 35 days. Amazon RDS automated backups provide point-in-time recovery within the retention period (up to 35 days) by storing daily snapshots and transaction logs, allowing recovery to any second. Option A is incorrect because manual snapshots every hour would be costly and provide less granular recovery compared to automated backups with transaction logs. Option C is incorrect because pg_dump to S3 only provides daily full backups, not point-in-time recovery to an arbitrary second. Option D is incorrect because AWS Backup cross-region copies are for disaster recovery, not for local PITR, and would incur additional costs.

Answer

Take manual snapshots every hour and retain for 35 days

Answer

Disable automated backups and use pg_dump to S3 daily

Answer

Use AWS Backup to copy snapshots to another region daily

Question 12

A company uses Amazon DynamoDB Global Tables for a multi-region application. The table is configured with on-demand capacity. The application writes data in the us-east-1 region and reads from us-west-2. Users in us-west-2 report that data written in us-east-1 is not appearing in us-west-2 within the expected replication latency of under 5 seconds. Instead, replication sometimes takes up to 30 seconds. Which two factors could be causing this increased replication latency? (Choose two.)

Accepted Answer

High network latency or packet loss between us-east-1 and us-west-2.. Options B and E are correct. Option B: High network latency or packet loss between the two regions directly increases replication time. Option E: A large volume of writes creates a backlog in the Global Tables replication stream, causing delays. Option A is incorrect because reading before replication completes is a symptom, not a cause of increased latency. Option C is incorrect because read capacity in a replica region does not affect replication latency; replication uses write capacity. Option D is incorrect because on-demand capacity automatically scales and does not cause write throttling.

Answer

The application is reading from the us-west-2 table before replication completes.

Answer

The read capacity in us-west-2 is insufficient, causing read throttling.

Answer

The on-demand capacity mode is causing write throttling in us-east-1.

Question 13

A developer is configuring an Amazon RDS for PostgreSQL DB instance. The application connects using IAM database authentication. Which setting must be enabled on the DB instance for IAM authentication to work?

Accepted Answer

Set the 'rds.force_ssl' parameter to 1.. IAM database authentication for Amazon RDS PostgreSQL requires an encrypted connection to protect the authentication token. Setting the 'rds.force_ssl' parameter to 1 enforces TLS/SSL connections between the client and the database, which is a prerequisite for IAM authentication. Option A is incorrect because the port (default 5432) does not need to change for IAM. Option C is incorrect because the DB instance can be private within a VPC; IAM authentication works over private or public connections as long as TLS is enforced. Option D is incorrect because the master username is not changed; IAM authentication uses database users that are mapped to IAM identities.

Answer

Set the database port to 5432.

Answer

Ensure the DB instance is publicly accessible.

Answer

Change the master username to 'iam_user'.

Question 14

A company is migrating a 10 TB SQL Server database to Amazon RDS for SQL Server. They need to minimize the migration time and cost. Which approach should they use?

Accepted Answer

Use AWS DMS with a full load and ongoing replication. AWS DMS with a full load and ongoing replication is the most efficient approach for migrating a 10 TB SQL Server database to Amazon RDS for SQL Server because it performs a one-time full load of the existing data and then continuously replicates ongoing changes, minimizing downtime. DMS handles schema conversion automatically for homogeneous migrations (SQL Server to SQL Server) and supports resumable tasks, which reduces the risk of restarting from scratch on failure. This approach balances speed and cost by using the network for data transfer without the overhead of physical media or manual restore steps.

Answer

Use AWS Snowball Edge to transfer backup files

Answer

Use AWS Schema Conversion Tool to convert schema and then bulk insert

Answer

Use native SQL Server backup to S3 and restore to RDS

Question 15

Refer to the exhibit. A company uses this DynamoDB table to store user session data. The application frequently queries by user_id alone to get all sessions for a user. However, the query is slow. What is the most likely cause?

Accepted Answer

The table's partition key is session_id, not user_id, so querying by user_id requires a scan.. The table's primary key is session_id, not user_id. Querying by user_id without a secondary index forces DynamoDB to perform a full table scan, which reads every item and is significantly slower than a query operation. This is the most likely cause of the slow performance.

Answer

The table has no sort key on user_id.

Answer

The table has too many items, causing slow scans.

Answer

The provisioned read capacity is too low.

Question 16

A company is designing a new application that requires a relational database with read replicas for reporting. The application has unpredictable traffic patterns. The company wants to minimize operational overhead and automatically scale compute capacity. Which TWO services should the company consider?

Accepted Answer

Amazon Aurora Serverless v2. The company requires a relational database with read replicas for reporting, minimal operational overhead, and automatic scaling of compute capacity. Amazon Aurora Serverless v2 (D) meets all these requirements: it is a relational database compatible with PostgreSQL and MySQL, automatically scales compute capacity based on demand, and supports up to 15 read replicas for reporting workloads. Amazon RDS Proxy (E) provides connection pooling to handle unpredictable traffic patterns efficiently, reducing overhead and improving scalability. Together, these two services fulfill the requirements without the need for an additional database instance, making option C unnecessary.

Answer

Amazon DynamoDB Accelerator (DAX)

Answer

Amazon RDS for MySQL with Multi-AZ

Answer

Amazon RDS for PostgreSQL with read replicas

Question 17

A company is using Amazon DynamoDB with Auto Scaling enabled. The database specialist notices that write traffic is being throttled occasionally. Which TWO factors could cause throttling despite Auto Scaling?

Accepted Answer

The write traffic exceeds the maximum provisioned capacity that was set for Auto Scaling.. Auto Scaling in DynamoDB operates within a maximum provisioned capacity ceiling. If write traffic exceeds this configured maximum, Auto Scaling cannot increase capacity further, leading to throttling. The service will return ProvisionedThroughputExceededException for requests that exceed the set maximum.

Answer

The table has Global Tables enabled, causing cross-region replication overhead.

Answer

Auto Scaling is not configured to scale up quickly enough for sudden traffic spikes.

Answer

DynamoDB Accelerator (DAX) is not caching write operations.

Question 18

A company uses Amazon DynamoDB for a shopping cart application. During a flash sale, write requests are throttled due to hot partitions. The access pattern is evenly distributed across items, but the partition key is the customer ID. Which design change would best mitigate throttling?

Accepted Answer

Enable DynamoDB adaptive capacity.. DynamoDB adaptive capacity automatically adjusts throughput capacity based on traffic patterns, which helps mitigate hot partitions by redistributing unused capacity from less-accessed partitions to heavily accessed ones. This is ideal for the flash sale scenario where write requests are throttled due to uneven access across customer ID partitions, even though the overall access pattern is evenly distributed.

Answer

Change the partition key to a single value for all items.

Answer

Increase the provisioned write capacity to a higher fixed value.

Answer

Add a DAX cluster in front of DynamoDB.

Question 19

A company is designing a database for a global e-commerce platform with strong consistency requirements. The database must support cross-region disaster recovery with RPO < 1 second and RTO < 1 minute. Which TWO AWS database services meet these requirements?

Accepted Answer

Amazon Aurora Global Database. Amazon Aurora Global Database uses storage-based replication with a typical latency of under 1 second, supporting cross-region disaster recovery with an RPO of less than 1 second and an RTO of less than 1 minute by promoting a secondary region to primary. Amazon DynamoDB Global Tables provide multi-region, fully replicated tables with strong consistency and automatic failover, achieving RPO of less than 1 second and RTO of less than 1 minute through active-active replication.

Answer

Amazon RDS Multi-AZ

Answer

Amazon Redshift with cross-region snapshot copy

Answer

Amazon ElastiCache for Redis with Global Datastore

Question 20

A company runs a critical Oracle database on Amazon RDS. The database has a large table that is frequently accessed by multiple applications. The team wants to implement caching to reduce the load on the database. The cached data must be strongly consistent with the database. Which caching strategy should they use?

Accepted Answer

Write-through cache using Amazon ElastiCache. The write-through cache strategy ensures that every write to the database also updates the cache synchronously, so the cached data is always strongly consistent with the database. This is critical for the Oracle RDS workload where multiple applications require immediate consistency. Amazon ElastiCache (Redis or Memcached) supports write-through by updating the cache on every write operation, preventing stale reads.

Answer

Eventual consistency with DynamoDB Accelerator (DAX)

Answer

Read-only cache with Amazon ElastiCache

Answer

Lazy loading with cache-aside pattern