DBS-C01 Monitoring and Troubleshooting Practice Test 9 — 15 Questions

Question 1

A DBA is investigating a sudden increase in database connections to an Amazon RDS for SQL Server instance. The application is running on Amazon EC2 instances behind an Application Load Balancer. Which tool can provide real-time information about active connections?

Accepted Answer

Amazon RDS Performance Insights. Option C is correct because RDS Performance Insights shows active session information including connections. Option A is wrong because CloudTrail tracks API calls, not connections. Option B is wrong because VPC Flow Logs track network traffic, not database connections. Option D is wrong because Trusted Advisor gives best practice checks, not real-time connections.

Answer

AWS Trusted Advisor

Answer

VPC Flow Logs

Answer

AWS CloudTrail

Question 2

A company is migrating their on-premises Oracle database to Amazon RDS for Oracle. They need to ensure minimal downtime. During the migration, they observe that the change data capture (CDC) is falling behind. What is the most effective approach to catch up?

Accepted Answer

Increase the instance size of the target RDS instance. Option B is correct because increasing the instance size provides more resources for replication. Option A is wrong because pausing replication would increase lag. Option C is wrong because switching to full load would cause downtime. Option D is wrong because disabling logging would break CDC.

Answer

Disable supplemental logging on the source

Answer

Pause the CDC task and resume later

Answer

Stop the CDC and perform a full load migration

Question 3

A company runs a document database using Amazon DocumentDB. They notice that some queries are taking much longer than expected. The explain plan shows a COLLSCAN. Which action would most improve query performance?

Accepted Answer

Create appropriate indexes on the fields used in query filters. Option A is correct because creating an index on the queried fields avoids collection scans. Option B is wrong because increasing instance size helps but doesn't address the root cause. Option C is wrong because changing consistency level affects read freshness, not performance. Option D is wrong because increasing storage doesn't improve query speed.

Answer

Increase the instance size to the next tier

Answer

Change the read consistency from eventual to strong

Answer

Increase the storage allocated to the instance

Question 4

A company uses Amazon DynamoDB global tables for a multi-region application. They notice that writes in one region are not appearing in another region after several minutes. What should they check first?

Accepted Answer

Check the ReplicationLatency metric in Amazon CloudWatch. Option C is correct because ReplicationLatency metric shows delay between regions. Option A is wrong because Streams are used for replication; check the metric first. Option B is wrong because auto scaling affects capacity, not replication. Option D is wrong because table size doesn't directly cause replication delay.

Answer

Verify that auto scaling is configured identically in both regions

Answer

Ensure DynamoDB Streams are enabled on the table

Answer

Check the table size in both regions

Question 5

Which TWO metrics should be monitored to detect an Amazon RDS for MySQL instance that is experiencing memory pressure? (Choose 2.)

Accepted Answer

SwapUsage. B and D are correct. SwapUsage indicates memory pressure when it exceeds 0. FreeableMemory shows available memory. A is wrong because CPUUtilization is CPU, not memory. C is wrong because DatabaseConnections affects memory but is indirect. E is wrong because ReadIOPS is disk I/O.

Answer

DatabaseConnections

Answer

ReadIOPS

Answer

CPUUtilization

Question 6

Which THREE actions should be taken to troubleshoot a high number of ThrottlingExceptions from Amazon DynamoDB? (Choose 3.)

Accepted Answer

Examine the ConsumedWriteCapacity and ThrottledWriteCount metrics in CloudWatch. A, C, D are correct. Examining CloudWatch metrics helps identify throttling patterns. Implementing exponential backoff is a best practice. Increasing provisioned capacity resolves throttling. B is wrong because enabling DynamoDB Streams does not affect throttling. E is wrong because changing consistency model does not affect write throttling.

Answer

Enable DynamoDB Streams to offload writes

Answer

Change the read consistency to eventual

Question 7

Which TWO tools can be used to monitor query performance in Amazon Aurora MySQL? (Choose 2.)

Accepted Answer

Amazon RDS Performance Insights. A and D are correct. Performance Insights provides database performance analysis. Enhanced Monitoring provides OS-level metrics. B is wrong because CloudTrail logs API calls. C is wrong because VPC Flow Logs show network traffic. E is wrong because AWS Config tracks resource configuration.

Answer

AWS Config

Answer

VPC Flow Logs

Answer

AWS CloudTrail

Question 8

Refer to the exhibit. An IAM policy is attached to a user. The user reports that they cannot delete the production-db database. Which statement best explains the behavior?

Accepted Answer

An explicit Deny statement prevents the deletion of the production-db instance. Option C is correct because an explicit Deny overrides any Allow. The Deny statement specifically denies DeleteDBInstance on that resource. Option A is wrong because the policy allows CreateDBInstance. Option B is wrong because DescribeDBInstances is allowed. Option D is wrong because the Deny is explicitly on the production-db ARN.

Answer

The user needs additional permissions to delete any DB instance

Answer

The user does not have permission to describe DB instances

Answer

The user does not have permission to create a DB instance

Question 9

Refer to the exhibit. A developer runs the AWS CLI command and receives the output shown. What is this output?

Accepted Answer

The DNS endpoint of the DB instance. Option C is correct. The output is the DNS endpoint of the RDS instance. Option A is wrong because it's not an IP address. Option B is wrong because Resource ID looks different. Option D is wrong because the reader endpoint includes '-ro'.

Answer

The private IP address of the DB instance

Answer

The reader endpoint of a Multi-AZ cluster

Answer

The resource ID of the DB instance

Question 10

Refer to the exhibit. A DBA sees the above log entries for an Amazon Aurora MySQL cluster. What is the most likely cause?

Accepted Answer

There is underlying storage corruption. Option D is correct because the logs indicate table corruption and page corruption, typically due to underlying storage issues. Option A is wrong because connection issues would show different errors. Option B is wrong because backup restore would not cause corruption. Option C is wrong because replication lag shows different symptoms.

Answer

The reader instance is lagging behind the writer

Answer

The DB instance has run out of connections

Answer

A recent backup restore operation failed

Question 11

A database administrator notices that an Amazon RDS for MySQL instance's CPU utilization is consistently above 80% during peak hours. The DB instance is a db.r5.large with 16 GB memory and 500 GB gp2 storage. The application is a read-intensive web application. Which action is MOST effective to reduce CPU load without significant cost increase?

Accepted Answer

Create a read replica and redirect read traffic to it. Option B is correct because creating a read replica offloads read traffic from the primary instance, reducing CPU utilization without requiring a larger instance or more storage. Option A increases cost significantly. Option C may not help if the issue is CPU, not I/O. Option D increases storage but does not directly reduce CPU.

Answer

Increase the instance size to db.r5.xlarge

Answer

Enable Performance Insights to identify slow queries and optimize them

Answer

Increase the allocated storage to 1000 GB to improve I/O performance

Question 12

A team is troubleshooting an Amazon Aurora MySQL cluster where the writer instance fails over unexpectedly every few days. The failover is not triggered by manual intervention or maintenance events. CloudWatch metrics show that the failover occurs when the replica lag on the reader instances spikes to over 10 seconds. What is the MOST likely cause of the failover?

Accepted Answer

The reader instances are under-provisioned and cannot keep up with the write rate from the writer. Option D is correct because if the reader instances are overloaded, they may not be able to apply changes quickly enough, causing replica lag. The failover could be due to the failover priority settings or a health check failure. Option A is incorrect because storage issues would affect both writer and readers. Option B is incorrect because an oversized instance would reduce lag, not increase it. Option C is incorrect because long-running queries on the writer would not directly cause replica lag on readers.

Answer

The reader instances are over-provisioned, causing them to become idle and drop connections

Answer

The Aurora cluster is experiencing a storage subsystem bottleneck in a single Availability Zone

Answer

The writer instance is running a long-running transaction that blocks replication

Question 13

A company uses Amazon DynamoDB with auto scaling enabled. During a sales event, the write capacity consumption increases, but the table does not scale up as expected, resulting in throttled requests. The table has read/write capacity mode set to 'Provisioned' with auto scaling configured. What should the team check first to troubleshoot the issue?

Accepted Answer

Check the target utilization percentage in the auto scaling policy. Option B is correct because auto scaling uses a target utilization percentage; if it's set too high, it may not trigger scaling soon enough. Option A is incorrect because auto scaling controls the provisioned capacity, not the table class. Option C is incorrect because auto scaling does not require manual approval. Option D is incorrect because auto scaling can increase capacity up to the maximum limit, regardless of the GSI.

Answer

Verify that the auto scaling role has the necessary IAM permissions

Answer

Check whether the table class is DynamoDB Standard-IA

Answer

Check if a global secondary index (GSI) has its own write capacity that is throttling

Question 14

A company is using Amazon Redshift for data warehousing. The users report that queries are slow, and the CloudWatch metric 'CPUUtilization' shows high usage. The cluster has 4 dc2.large nodes. The administrator runs the following query: SELECT * FROM stl_query WHERE starttime > '2023-12-01' ORDER BY duration DESC LIMIT 10; This shows that the longest query runs for over 5 minutes. Which of the following is the MOST effective way to improve query performance?

Accepted Answer

Add more nodes to the cluster (scale out). Option C is correct because distributing data across more nodes allows parallel processing, which reduces query execution time. Option A is incorrect because the issue is CPU, not storage. Option B is incorrect because WLM queues manage concurrency, not individual query performance. Option D is incorrect because vacuum reclaims space but does not directly speed up queries.

Answer

Increase the size of the cluster volume by adding more storage

Answer

Run the VACUUM command to reclaim space and improve query performance

Answer

Modify the workload management (WLM) queue to increase concurrency

Question 15

A company is running a MongoDB-compatible Amazon DocumentDB cluster with one writer and two readers. The application writes a large amount of data during batch processing, and after a batch completes, the writer's CPU is high, and the readers have significant replica lag. The team wants to reduce replica lag without affecting the batch performance. What should they do?

Accepted Answer

Increase the instance size of the readers to improve apply throughput. Option D is correct because the replica lag is due to the readers applying writes from the oplog; increasing the reader instance size gives them more CPU and memory to apply writes faster. Option A is incorrect because increasing the writer size does not directly help readers. Option B is incorrect because decreasing the batch size reduces writes but the team wants to maintain performance. Option C is incorrect because changing the storage type does not affect replica lag.

Answer

Change the storage type to Provisioned IOPS on all instances

Answer

Reduce the batch size to lower the write rate

Answer

Increase the instance size of the writer to handle the batch faster