DBS-C01 Practice Test 4 — 25 Questions

Question 1

Arrange the steps to migrate an on-premises Oracle database to Amazon RDS for Oracle using AWS DMS (Database Migration Service) in the correct order.

Accepted Answer

Launch the DMS replication instance, then configure the source and target endpoints, then create the migration task, then monitor the migration task.. DMS migration requires setting up the replication instance, configuring endpoints with proper source database settings for CDC, creating a migration task, and monitoring for completion.

Answer

Configure the source and target endpoints, then launch the DMS replication instance, then create the migration task, then monitor the migration task.

Answer

Launch the DMS replication instance, then create the migration task, then configure the source and target endpoints, then monitor the migration task.

Answer

Configure the source and target endpoints, then launch the DMS replication instance, then monitor the migration task, then create the migration task.

Question 2

A company is designing a multi-tenant application using Amazon Aurora MySQL. Each tenant's data must be isolated from others. They need to encrypt data at rest with a unique AWS KMS key per tenant. How can this be achieved?

Accepted Answer

Launch separate Aurora clusters for each tenant, each with its own KMS key for encryption at rest.. To encrypt each tenant's data with a unique KMS key, you must launch separate Aurora clusters for each tenant, because encryption at rest is applied at the cluster level using a single KMS key. Each cluster can be configured with its own KMS key, providing tenant isolation. This approach ensures that data for each tenant is encrypted with a distinct key.

Answer

Create separate databases within the same Aurora cluster and assign a different KMS key to each database.

Answer

Use client-side encryption with different KMS keys per tenant before inserting data into the database.

Answer

Use a single Aurora cluster with row-level encryption using different KMS keys per tenant.

Question 3

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 most likely reason the query returns no results is that the log stream format uses a different field name for the error message than the one referenced in the query. In CloudWatch Logs Insights, the query must reference fields exactly as they appear in the log events. If the logs use a different key (e.g., 'message' vs 'errorMessage'), the filter will not match.

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 4

A company is migrating an on-premises Microsoft SQL Server database to Amazon RDS for SQL Server. The database supports a line-of-business application that requires high availability and automatic failover within a single AWS Region. The company wants to minimize downtime during the migration and ensure that the database can automatically recover from an Availability Zone failure. Which feature should the company implement?

Accepted Answer

Multi-AZ deployment with a standby replica in another Availability Zone. For Amazon RDS for SQL Server, Multi-AZ deployment provides a synchronous standby replica in a different Availability Zone and automatic failover in case of an AZ failure. This is the standard high availability feature offered by RDS. Read replicas are for read scaling and do not provide automatic failover. AWS DMS is for migration. Always On Availability Groups are supported but require additional configuration and are not the primary RDS high availability feature. Therefore, Multi-AZ deployment is the correct choice.

Answer

AWS Database Migration Service (AWS DMS) with ongoing replication

Answer

Amazon RDS for SQL Server with Always On Availability Groups

Answer

Read replicas in multiple Availability Zones

Question 5

A company is deploying a new web application that uses Amazon RDS for PostgreSQL. The database must be highly available with automatic failover across two Availability Zones. Which deployment option meets this requirement?

Accepted Answer

Deploy RDS PostgreSQL with Multi-AZ configuration.. Amazon RDS Multi-AZ deployment automatically provisions and maintains a synchronous standby replica in a different Availability Zone. If the primary DB instance fails, Amazon RDS automatically fails over to the standby, providing high availability with automatic failover across two AZs. This meets the requirement without manual intervention or application changes.

Answer

Deploy RDS PostgreSQL in a cross-region replication setup.

Answer

Deploy RDS PostgreSQL in a single Availability Zone.

Answer

Deploy RDS PostgreSQL with a read replica in another AZ.

Question 6

A developer is troubleshooting an application that writes to an Amazon ElastiCache for Redis cluster. The application occasionally fails with 'OOM command not allowed when used memory > maxmemory'. What is the most likely cause?

Accepted Answer

The cluster's maxmemory-policy is set to noeviction.. The error 'OOM command not allowed when used memory > maxmemory' occurs when Redis has reached its configured memory limit and the eviction policy is set to 'noeviction', which prevents any further writes. Option B is correct because 'noeviction' causes Redis to return an error instead of evicting keys. Option A is incorrect because the 'maxclients' limit produces a different error ('max number of clients reached'). Option C is incorrect because keyspace notifications do not affect memory limits. Option D is incorrect because cross-slot commands relate to cluster mode, not memory errors.

Answer

The cluster's maxclients limit has been reached.

Answer

The cluster has too many keyspace notifications enabled.

Answer

The cluster is in cluster mode and cross-slot commands are used.

Question 7

A company is designing a new e-commerce platform using Amazon DynamoDB. The workload requires single-digit millisecond latency for user session data, which is accessed by session token. The session data is temporary and should be automatically deleted after 24 hours. Which DynamoDB design should the database specialist recommend?

Accepted Answer

Enable DynamoDB Time to Live (TTL) on the session token attribute. DynamoDB Time to Live (TTL) automatically deletes expired items after a specified timestamp, making it ideal for session data that must be removed after 24 hours. This approach requires no additional infrastructure, meets the single-digit millisecond latency requirement by using the session token as the primary key, and ensures automatic cleanup without manual intervention or added cost.

Answer

Create an AWS Lambda function that runs every hour and deletes expired session data

Answer

Store session data in Amazon S3 with a lifecycle policy to delete objects after 24 hours

Answer

Use DynamoDB Accelerator (DAX) to cache session data and set a 24-hour TTL on the cache

Question 8

A database specialist is troubleshooting a performance issue on a self-managed PostgreSQL database that they plan to migrate to Amazon RDS. The database has a high number of 'idle in transaction' connections. What is the impact of these connections on the database?

Accepted Answer

They hold locks and prevent cleanup of dead tuples, leading to bloat.. Idle-in-transaction connections hold locks and prevent PostgreSQL's autovacuum from cleaning up dead tuples, leading to table bloat and performance degradation. Option A is wrong because idle transactions do not cause constant polling; CPU usage remains low. Option C is wrong because they do not prevent new connections from being established unless the max_connections limit is reached. Option D is wrong because idle transactions do not significantly increase write-ahead logging.

Answer

They increase CPU usage due to constant polling.

Answer

They prevent new connections from being established.

Answer

They cause increased disk I/O from write-ahead logging.

Question 9

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

Accepted Answer

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

Answer

Upgrade to a larger instance type.

Answer

Create a read replica and run reports on the replica.

Answer

Partition the table by order_date.

Question 10

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

Accepted Answer

Innodb_row_lock_current_waits. InnoDB row lock waits directly indicate contention for row-level locks, which is a common cause of high Threads_running when many queries are blocked waiting for locks held by other transactions. Monitoring Innodb_row_lock_current_waits reveals the number of transactions currently waiting for a row lock, pinpointing lock contention as the root cause of slow queries and elevated running threads.

Answer

Queries_per_second

Answer

Slow_queries

Answer

Threads_connected

Question 11

A company is migrating an on-premises Oracle database to Amazon Aurora PostgreSQL. The database contains a large table that is partitioned by date. The company wants to minimize downtime during migration and ensure compatibility. Which TWO actions should the company take?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication to migrate the data.. AWS DMS with ongoing replication (change data capture) allows continuous synchronization from the source Oracle database to the target Aurora PostgreSQL, minimizing downtime by keeping the target nearly up-to-date until the final cutover. This approach supports large partitioned tables and reduces the migration window compared to a full load only.

Answer

Migrate the database using a full load only and accept downtime.

Answer

Use AWS Schema Conversion Tool (SCT) to convert the schema automatically without any manual adjustments.

Answer

Replace the Oracle database with Amazon RDS for MySQL.

Question 12

A database specialist needs to monitor the number of deadlocks occurring in an Amazon RDS for SQL Server DB instance. Which CloudWatch metric should be used?

Accepted Answer

Deadlocks. The 'Deadlocks' metric in Amazon RDS for SQL Server specifically counts the number of deadlocks that occur on the DB instance. Option A is incorrect because 'BlockedTransactions' tracks transactions that are blocked, not deadlocks. Option C is incorrect because 'DatabaseConnections' is a count of active connections, not related to deadlocks. Option D is incorrect because 'LockWaits' measures the number of lock waits, which is a different contention event.

Answer

BlockedTransactions

Answer

DatabaseConnections

Answer

LockWaits

Question 13

A company is running a MongoDB-compatible Amazon DocumentDB cluster. The application team reports that write operations are failing intermittently with a `WriteConcernError` indicating that the write concern could not be satisfied. The cluster has one primary and two replicas. What is the MOST likely cause of this issue?

Accepted Answer

One of the replicas is down or experiencing high replication lag. The WriteConcernError occurs because the write concern requires acknowledgment from a certain number of replicas. With a cluster of one primary and two replicas, if any replica is down or has high replication lag, the write concern requirement cannot be satisfied. Option A is correct because that is the most likely cause. Option B is incorrect because the cluster has enough replicas for majority write concern if all are healthy. Option C is incorrect because read preference does not affect write operations. Option D is incorrect because the primary being overloaded with reads would not cause a WriteConcernError; it would affect performance but not the ability to satisfy write concern.

Answer

The cluster does not have enough replica instances to satisfy the write concern

Answer

The application is using an incorrect read preference

Answer

The primary instance is overloaded with read requests

Question 14

Which TWO factors should be considered when choosing between Amazon DynamoDB and Amazon RDS for MySQL for a new e-commerce application with variable traffic patterns?

Accepted Answer

Operational overhead: DynamoDB is serverless, RDS requires patching and provisioning.. DynamoDB is a fully managed serverless service that eliminates the need for patching, provisioning, or managing servers, whereas Amazon RDS for MySQL requires manual patching, scaling, and instance provisioning. This operational overhead difference is critical for variable traffic patterns, as DynamoDB automatically handles infrastructure management, reducing administrative burden.

Answer

Ability to perform complex joins and aggregations: DynamoDB supports SQL-like queries.

Answer

Support for ACID transactions in both databases.

Answer

Encryption at rest is only available for RDS.

Question 15

A company is migrating a PostgreSQL database to Amazon RDS for PostgreSQL. They want to automate the deployment of the RDS instance using infrastructure as code. Which AWS service should they use?

Accepted Answer

AWS CloudFormation.. AWS CloudFormation is the correct service for automating the deployment of an RDS for PostgreSQL instance using infrastructure as code. It allows you to define the entire RDS instance configuration—including DB instance class, storage, backup retention, and security groups—in a declarative JSON or YAML template, which can be version-controlled and reused for consistent, repeatable deployments.

Answer

Amazon EC2 Auto Scaling.

Answer

AWS Management Console.

Answer

AWS Command Line Interface (CLI).

Question 16

A company uses Amazon DynamoDB with fine-grained access control using IAM policies. A developer reports that an application role can read and write to the 'orders' table but cannot perform a Scan operation on a Global Secondary Index (GSI). The IAM policy attached to the role includes 'dynamodb:Scan' and the resource ARN for the table. What is the likely reason for this failure?

Accepted Answer

The IAM policy does not include the GSI's ARN in the resource statement.. DynamoDB IAM policies require the resource ARN to match the specific table or index being accessed. A GSI has its own ARN (table-name/index/index-name), so a policy that only includes the base table ARN will allow Scan on the table but deny Scan on the GSI. The fix is to add the GSI's ARN to the Resource element of the policy.

Answer

The policy has a condition that restricts Scan operations based on the time of day.

Answer

The role does not have permission to read from the base table.

Answer

The IAM policy does not allow the 'dynamodb:Scan' action on the table.

Question 17

A company is designing a database for a social media application that needs to handle friend-of-friend queries and recommendation engine traversals. Which AWS database is best suited?

Accepted Answer

Amazon Neptune. Amazon Neptune is a fully managed graph database service optimized for storing and querying highly connected data. It supports both property graph (Apache TinkerPop/Gremlin) and RDF (SPARQL) models, making it ideal for friend-of-friend queries and recommendation engine traversals that require navigating complex relationships with low latency.

Answer

Amazon DynamoDB

Answer

Amazon DocumentDB (with MongoDB compatibility)

Answer

Amazon ElastiCache for Redis

Question 18

A company is using Amazon ElastiCache for Redis as a caching layer. The application is experiencing higher latency than expected. The team suspects that cache evictions are occurring due to memory pressure. Which ElastiCache metric should be monitored to confirm this?

Accepted Answer

Evictions. The `Evictions` metric in ElastiCache for Redis tracks the number of keys evicted due to memory pressure, which directly indicates cache evictions. Option A is incorrect because `CurrConnections` shows the number of current client connections, not evictions. Option C is incorrect because `ReplicationLag` measures the delay between the primary and replica nodes, not evictions. Option D is incorrect because `CacheHits` shows the number of successful key lookups, not evictions.

Answer

CurrConnections

Answer

ReplicationLag

Answer

CacheHits

Question 19

A company is migrating a 2 TB PostgreSQL database from on-premises to Amazon RDS for PostgreSQL with minimal downtime. The database is continuously updated. Which migration strategy should be used?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication from an on-premises source.. AWS DMS supports ongoing replication (change data capture, CDC) from an on-premises PostgreSQL source to Amazon RDS for PostgreSQL, enabling minimal downtime migration. The 2 TB size is well within DMS's capabilities, and CDC captures incremental changes after the full load, allowing near-zero downtime cutover.

Answer

Use AWS Schema Conversion Tool (SCT) and AWS Snowball to transfer data.

Answer

Use AWS Database Migration Service with a full load only, then cut over.

Answer

Use pg_dump and pg_restore during a maintenance window.

Question 20

A company wants to migrate a 500 GB SQL Server database to Amazon RDS for SQL Server with the least amount of downtime. The on-premises network has a 1 Gbps connection to AWS. Which approach should be used?

Accepted Answer

Use AWS DMS with ongoing replication from on-premises to RDS. AWS DMS with ongoing replication (change data capture, CDC) allows you to perform a full load of the 500 GB database while continuously replicating ongoing changes from the on-premises SQL Server to Amazon RDS for SQL Server. This minimizes downtime to a brief cutover window when you stop writes on the source and redirect traffic to the target. The 1 Gbps connection is sufficient for the initial load and ongoing replication, making this the most effective approach for minimal downtime.

Answer

Use AWS Snowball to transfer the database backup, then restore to RDS

Answer

Copy database files to S3 and then use RDS import

Answer

Use native SQL Server backup to S3, then restore to RDS