DBS-C01 Practice Exam 51 — 20 Questions

Question 1

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 2 TB in size. The company wants to minimize downtime during the migration. Which AWS service should be used to perform an online migration with minimal downtime?

Accepted Answer

AWS Database Migration Service (DMS). AWS Database Migration Service (DMS) supports ongoing replication to minimize downtime. Snowball is for offline data transfer. S3 is not a migration service. Direct Connect provides a dedicated network connection but is not a migration service itself.

Answer

AWS Direct Connect

Answer

AWS Snowball

Answer

Amazon S3

Question 2

An application is experiencing increased latency when writing to an Amazon DynamoDB table. The table uses on-demand capacity mode. The CloudWatch metric 'WriteThrottleEvents' is zero. What is the most likely cause of the increased latency?

Accepted Answer

A hot partition is causing excessive write traffic to a single partition.. Option C is correct because on-demand tables can throttle if you exceed the previous peak traffic by more than double in a short time, but since WriteThrottleEvents is zero, latency is likely due to hot partitions. Option A is wrong because throttling would show WriteThrottleEvents > 0. Option B is wrong because insufficient WCUs is not applicable for on-demand. Option D is wrong because while DAX can reduce read latency, it does not affect write latency.

Answer

The write capacity units (WCUs) are set too low.

Answer

DynamoDB Accelerator (DAX) is not configured for writes.

Answer

The table is experiencing write throttling due to exceeding the provisioned write capacity.

Question 3

A company is running an Amazon RDS for PostgreSQL DB instance with Multi-AZ. The database experiences a failover during a maintenance window. After the failover, the application connection pool continues to use the old primary endpoint, causing connection errors. What is the BEST way to ensure application connections automatically redirect to the new primary after a failover?

Accepted Answer

Use the RDS endpoint (CNAME) provided by RDS, which automatically points to the primary instance.. Option C is correct because using the RDS DNS CNAME record (which points to the primary instance and automatically updates after failover) ensures connections are redirected. Option A is wrong because modifying the connection string manually is not automated. Option B is wrong because a custom DNS solution adds complexity and is unnecessary. Option D is wrong because the RDS endpoint is dynamic and not static; the DNS record handles the failover.

Answer

Create a custom Route 53 failover routing policy pointing to both DB instances.

Answer

Modify the application connection string to point to the new primary IP address after each failover.

Answer

Configure the application to use a static IP address of the primary instance.

Question 4

A company is running an Amazon RDS for MySQL DB instance with Multi-AZ. The company wants to perform a major version upgrade with minimal downtime. Which TWO actions should be taken? (Choose TWO.)

Accepted Answer

Use the AWS Management Console to modify the DB instance and apply the upgrade immediately.. Option A is correct because enabling automatic minor version upgrades is good practice but not required for major upgrades. Option B is correct because creating a read replica, upgrading it first, and then promoting it minimizes downtime. Option D is also correct (but wait, the question says 'Which TWO' and there are exactly two correct: B and D? Actually, A is not required for major upgrades. Let's check: Option B and D are correct: B: create read replica, upgrade, promote; D: perform the upgrade on the standby first. Option A is not directly related. Option C is wrong because it causes downtime. Option E is wrong because it is not supported for major upgrades. So correct: B and D.

Answer

Use the AWS CLI to modify the DB instance with the --allow-major-version-upgrade flag.

Answer

Enable automatic minor version upgrades on the DB instance.

Answer

Take a snapshot and restore to the new version.

Question 5

Which TWO AWS services can be used to monitor and set alarms on Amazon RDS database performance metrics? (Choose two.)

Accepted Answer

Amazon RDS Enhanced Monitoring. CloudWatch monitors metrics and can set alarms; Enhanced Monitoring provides OS-level metrics. RDS Performance Insights is for performance analysis, not alarms.

Answer

Amazon RDS Performance Insights

Answer

AWS Trusted Advisor

Answer

AWS CloudTrail

Question 6

A company is using Amazon ElastiCache for Redis to cache database query results. They notice that the cache hit ratio is low and many requests are hitting the database. The 'Evictions' metric is high. What is the MOST likely cause?

Accepted Answer

The cache node is too small for the workload.. Option A is correct because high evictions indicate the cache is full, leading to item removal and low hit ratio. Option B is wrong because high latency does not directly cause evictions. Option C is wrong because insufficient replication factor does not cause evictions. Option D is wrong because encryption in transit does not affect cache performance.

Answer

The replication factor is insufficient.

Answer

Encryption in transit is enabled.

Answer

The application is experiencing high network latency.

Question 7

A company uses Amazon DynamoDB to store session data for a web application. The application is experiencing occasional throttling (ProvisionedThroughputExceededException) during peak hours. The DynamoDB table has on-demand capacity mode. Which combination of steps should be taken to resolve the issue?

Accepted Answer

Review the partition key design and consider using a write sharding pattern to distribute traffic evenly.. Option D is correct because on-demand tables can still throttle if a single partition receives more than 3,000 RCU or 1,000 WCU. Using adaptive capacity with a more uniform partition key distributes traffic. Option A is wrong because on-demand does not require adjusting RCU/WCU. Option B is wrong because auto scaling is for provisioned capacity. Option C is wrong because DAX is a caching layer that reduces read load but does not eliminate throttling for hot partitions.

Answer

Enable DynamoDB Accelerator (DAX) to cache the frequently accessed items.

Answer

Enable auto scaling for the table and set minimum and maximum capacity.

Answer

Switch to provisioned capacity and increase the read and write capacity units.

Question 8

A company has a production Amazon Aurora MySQL DB cluster with one writer and two reader instances. The application uses a custom connection pool that uses the writer endpoint for all database calls. The application is experiencing increased latency during peak hours. A database specialist suggests using the reader endpoint for read-only queries. What change is required on the application side to implement this recommendation?

Accepted Answer

Update the application's connection logic to use the cluster endpoint for writes and the reader endpoint for reads.. The application needs to differentiate between read and write queries and send read queries to the reader endpoint while write queries continue to use the writer endpoint. No changes to the Aurora cluster are needed; Aurora automatically handles connectivity to reader instances via the reader endpoint. The cluster endpoint remains unchanged for writes.

Answer

Modify the Aurora cluster to enable load balancing for the reader endpoint.

Answer

Create a new custom endpoint for read-only queries and use it instead of the reader endpoint.

Answer

Replace the writer endpoint with the reader endpoint in the connection pool configuration.

Question 9

A company is using Amazon Aurora MySQL-Compatible Edition. The database has frequent deadlocks, and the application team suspects that the isolation level is causing the issue. The current isolation level is REPEATABLE READ. The team wants to reduce deadlocks while maintaining data consistency. Which isolation level should be recommended?

Accepted Answer

READ COMMITTED. Option A is correct because READ COMMITTED reduces locking and is less prone to deadlocks compared to REPEATABLE READ, while still providing consistent reads at the statement level. Option B is wrong because READ UNCOMMITTED can cause dirty reads and is not typically used for transactional databases. Option C is wrong because SERIALIZABLE increases locking and can increase deadlocks. Option D is wrong because SNAPSHOT ISOLATION is not directly supported by MySQL; it is a SQL Server feature.

Answer

READ UNCOMMITTED

Answer

SNAPSHOT ISOLATION

Answer

SERIALIZABLE

Question 10

A company is using Amazon DynamoDB with provisioned capacity. The table's read capacity is consistently underutilized, but the write capacity is frequently maxed out. The team wants to optimize costs while maintaining performance. Which TWO actions should be taken?

Accepted Answer

Use DynamoDB Auto Scaling for write capacity.. Options B and C are correct because using DynamoDB Auto Scaling for writes will adjust capacity based on demand, and reducing provisioned reads to actual usage will save costs. Option A is wrong because switching to on-demand may increase costs if the workload is predictable. Option D is wrong because reducing writes would cause throttling. Option E is wrong because using DAX does not reduce write costs.

Answer

Switch the table to on-demand capacity mode.

Answer

Enable DynamoDB Accelerator (DAX) to offload reads.

Answer

Increase the provisioned write capacity to handle spikes.

Question 11

A company uses Amazon DynamoDB with provisioned capacity for a gaming application. During a new game launch, write traffic spikes to 2x the provisioned write capacity for 30 minutes. Some writes are throttled. The company wants to handle these predictable spikes without manual intervention. What is the MOST cost-effective solution?

Accepted Answer

Enable DynamoDB auto scaling with a target utilization of 70%.. Option D is correct because DynamoDB auto scaling adjusts capacity based on actual usage and can handle predictable spikes with minimal cost. Option A is wrong because switching to on-demand can be more expensive for predictable workloads. Option B is wrong because increasing capacity manually requires monitoring and intervention. Option C is wrong because SQS does not directly handle DynamoDB write throttling.

Answer

Increase the provisioned write capacity to 2x the baseline permanently.

Answer

Change the table to on-demand capacity mode.

Answer

Use Amazon SQS to buffer writes and process them later.

Question 12

A company uses Amazon RDS for PostgreSQL with Multi-AZ deployment. They experience increased write latency during peak hours. The DB instance size is db.r5.large. Which action would MOST effectively reduce write latency?

Accepted Answer

Disable the Multi-AZ feature and use asynchronous replication with a read replica for failover.. Multi-AZ deployments use synchronous standby; enabling Multi-AZ with one standby reduces latency overhead compared to two standbys.

Answer

Switch to a db.r5.xlarge instance type.

Answer

Enable the synchronous_commit parameter to 'off'.

Answer

Enable Multi-AZ with two standby replicas.

Question 13

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 500 GB and has a 4-hour downtime window. Which AWS service should be used to perform the migration with minimal downtime?

Accepted Answer

AWS Database Migration Service (DMS). Option B is correct because AWS DMS supports ongoing replication to minimize downtime during migration. Option A is wrong because AWS Snowball is for large data transfers but does not support ongoing replication. Option C is wrong because S3 is not a migration tool. Option D is wrong because RDS does not natively support Oracle Data Pump directly; DMS is the recommended service.

Answer

Oracle Data Pump using Amazon RDS option groups

Answer

AWS Snowball Edge

Answer

Amazon S3 Transfer Acceleration

Question 14

A company runs an Amazon RDS for MySQL DB instance with Multi-AZ. The application team reports that a recent schema change caused a significant increase in replication lag. The instance has a read replica in a different AWS Region. Which THREE actions should be taken to reduce replication lag?

Accepted Answer

Identify and optimize any long-running transactions or DDL statements that may be blocking replication.. Options A, C, and E are correct: Identifying and optimizing long-running transactions and DDL statements reduces lag. Monitoring replication metrics helps pinpoint the cause. Using a lower isolation level reduces locking. Option B is wrong because disabling binary logging stops replication entirely. Option D is wrong because increasing instance class may help but is not a targeted fix; the other options address common causes of lag.

Answer

Increase the DB instance class for both the primary and read replica to improve performance.

Answer

Disable binary logging on the primary instance to reduce I/O overhead.

Question 15

A company is running a production Amazon RDS for MySQL DB instance. The database size is 500 GB and the workload is write-heavy. The team notices that the automated backups are taking longer than expected and are impacting the performance during the backup window. Which action should be taken to minimize the performance impact?

Accepted Answer

Create a read replica and configure automated backups on the replica.. Option D is correct because creating a read replica and taking backups from it offloads the backup load from the primary instance. Option A is wrong because disabling backups is risky for production. Option B is wrong because it affects the start time but not the performance impact. Option C is wrong because increasing instance size may reduce backup duration but does not directly minimize the performance impact; it also adds cost.

Answer

Disable automated backups and rely on manual snapshots taken during off-peak hours.

Answer

Increase the DB instance size to improve backup performance.

Answer

Move the backup window to a time when the workload is lowest.

Question 16

A company is running Amazon RDS for Oracle with a Multi-AZ deployment. The database is experiencing performance degradation due to high I/O waits. The team suspects that the issue is related to the transaction log (redo log) writes. Which THREE metrics should be monitored in Amazon CloudWatch to diagnose the issue?

Accepted Answer

DiskQueueDepth. Options A, C, and E are correct because high redo log sync time, high redo log file sync waits, and high disk queue depth are indicators of I/O bottlenecks affecting redo log writes. Option B is wrong because read latency is not directly related to redo log writes. Option D is wrong because CPU utilization may be high but does not directly indicate redo log issues.

Answer

CPUUtilization

Answer

ReadLatency

Question 17

A developer accidentally deleted a table in an Amazon RDS for PostgreSQL DB instance. The instance has automated backups enabled with a retention period of 7 days. The deletion occurred 2 hours ago. What is the quickest way to recover the table?

Accepted Answer

Perform a point-in-time recovery to a time just before the deletion.. Option C is correct because point-in-time recovery restores the instance to a time before the deletion, and you can then extract the table. Option A is wrong because automated backups are not directly accessible as files. Option B is wrong because restoring from a snapshot would require a snapshot taken before deletion, which may not exist if the last snapshot was after deletion. Option D is wrong because the 'deleted' table is not in the current database.

Answer

Use PostgreSQL pg_dump to connect and dump the table from the current instance.

Answer

Download the automated backup file from S3 and restore the table.

Answer

Restore the DB instance from the latest automated snapshot.

Question 18

A database administrator notices that an Amazon Aurora MySQL DB cluster's primary instance is experiencing high CPU utilization due to a long-running analytical query. The application can tolerate eventual consistency. What is the MOST cost-effective solution to reduce CPU load on the primary instance?

Accepted Answer

Configure an Auto Scaling policy for Aurora Replicas and modify the application to use the reader endpoint.. Offloading read queries to Aurora Replicas is cost-effective and reduces primary load without additional infrastructure.

Answer

Create a read replica in a different region and route read traffic there.

Answer

Increase the instance size of the primary instance.

Answer

Enable Aurora Parallel Query on the cluster.

Question 19

A company uses Amazon DynamoDB with on-demand capacity for a gaming leaderboard. During a promotional event, write traffic spikes 10x, causing occasional 'ProvisionedThroughputExceededException' errors. The application retries with exponential backoff, but latency increases. The team notices that the 'ThrottledWriteRequests' metric spikes. What is the MOST cost-effective solution to handle these unpredictable spikes?

Accepted Answer

Continue using on-demand capacity but ensure the table has no throttling.. Option D is correct because on-demand capacity automatically scales to handle traffic spikes, eliminating throttling without manual intervention, and is cost-effective for unpredictable workloads. Option A is wrong because while DAX reduces read latency, it does not help with write throttling. Option B is wrong because auto scaling requires setting min/max capacity and may not react fast enough to sudden spikes. Option C is wrong because implementing a queue adds complexity and latency, and is not the simplest solution.

Answer

Implement DynamoDB Accelerator (DAX) to reduce read load.

Answer

Switch to provisioned capacity with auto scaling configured for the expected peak.

Answer

Use an Amazon SQS queue to buffer write requests before DynamoDB.

Question 20

A company is using Amazon RDS for Oracle with Automated Backups enabled. The database size is 1 TB. The company wants to improve the backup and restore performance. Which TWO actions should be taken? (Choose two.)

Accepted Answer

Use Provisioned IOPS storage for the database.. Option A is correct because enabling backup compression reduces backup size and speeds up transfers. Option B is correct because using Provisioned IOPS improves I/O performance for backups. Option C is wrong because increasing retention does not improve performance. Option D is wrong because disabling Multi-AZ reduces availability. Option E is wrong because using a smaller instance class would worsen performance.

Answer

Use a smaller DB instance class to reduce backup size.

Answer

Increase the backup retention period to 35 days.

Answer

Disable Multi-AZ to reduce backup time.