DBS-C01 Monitoring and Troubleshooting Practice Test 2 — 15 Questions

Question 1

You are managing an Amazon RDS for PostgreSQL Multi-AZ DB instance that handles a high-traffic e-commerce application. Recently, the database has been experiencing intermittent slowdowns during peak hours. You have enabled Enhanced Monitoring and Performance Insights. After reviewing the Performance Insights dashboard, you notice that the 'db.sql.queries.avg_latency' metric spikes during the slowdowns, and the top SQL queries are all simple SELECT statements on a frequently accessed 'orders' table. The table has over 10 million rows and is indexed on 'order_id', 'customer_id', and 'order_date'. The average query latency for these SELECT statements jumps from 5 ms to over 500 ms during the spikes. You also observe that the 'ReadIOPS' metric on the DB instance is consistently below the provisioned IOPS limit of the gp2 storage. The DB instance type is db.r5.large with 16 GB memory. The 'DatabaseConnections' metric shows that the number of connections is well within the max_connections limit (set to 200). However, the 'CPUCreditBalance' for the underlying EC2 instance, which is a T3 medium, drops to near zero during the spikes. The 'CPUUtilization' metric is below 50%. Which of the following is the MOST likely cause and the appropriate action to resolve the issue?

Accepted Answer

The issue is due to CPU credit exhaustion on the T3 instance. Change the DB instance class from db.t3.medium to a dedicated CPU instance type such as db.r5.large.. The correct answer is A. The 'CPUCreditBalance' dropping to near zero on a T3 instance indicates CPU credit exhaustion, which throttles the baseline CPU performance and causes query latency spikes. Even though 'CPUUtilization' is below 50%, T3 instances rely on CPU credits for burstable performance; when credits are exhausted, the instance is limited to the baseline (e.g., 10% for t3.medium), causing severe latency increases for simple SELECT statements. Moving to a dedicated CPU instance like db.r5.large eliminates credit-based throttling and provides consistent performance.

Answer

The issue is due to a memory bottleneck causing queries to spill to disk. Increase the instance memory by moving to a db.r5.xlarge instance.

Answer

The issue is caused by a connection pool exhaustion. Increase the max_connections parameter and use connection pooling.

Answer

The issue is caused by a missing index on the 'orders' table. Add a composite index on the columns used in the WHERE clauses.

Question 2

A database engineer is troubleshooting high CPU usage on an Amazon RDS for PostgreSQL instance. Amazon CloudWatch shows CPU Utilization consistently above 90% during business hours. Which combination of actions should the engineer take to identify the root cause? (Choose TWO.)

Accepted Answer

Review the slow query log to identify long-running queries.. Option B is correct because reviewing the slow query log directly identifies long-running queries that can cause sustained high CPU usage on RDS for PostgreSQL. Option D is correct because Performance Insights provides a visual dashboard of database load and top SQL queries, making it easy to pinpoint which queries are consuming the most CPU resources.

Answer

Enable Enhanced Monitoring and review OS process list.

Answer

Scale up the DB instance to a larger instance class.

Answer

Install pg_stat_statements extension and query it.

Question 3

A company runs a production Amazon DynamoDB table with on-demand capacity. The table stores session data for a web application. Recently, users have reported occasional slow response times. The operations team notices that the table's ConsumedWriteCapacityUnits metric shows occasional spikes that exceed the provisioned throughput (though on-demand auto-scales), and ThrottledWriteEvents metrics show occasional throttling. The application uses the AWS SDK with default retry logic. The database specialist is asked to investigate. Upon reviewing the table configuration, the specialist finds that the table has a simple primary key (partition key only) and the data access pattern is heavily skewed toward a small number of partition keys. The application writes in batches of 25 items using the BatchWriteItem API. What should the specialist recommend to reduce throttling and improve performance?

Accepted Answer

Implement write sharding by adding a random suffix to the partition key to distribute writes more evenly.. The correct answer is A because the throttling is caused by a hot partition: the table uses a single partition key, and writes are heavily skewed toward a few keys. By adding a random suffix to the partition key (write sharding), the writes are distributed evenly across all partitions, eliminating hot spots and reducing throttling. The on-demand capacity mode already handles overall throughput, but it cannot prevent throttling on individual partitions when access is skewed.

Answer

Increase the provisioned read capacity units to handle the load.

Answer

Switch the table to provisioned capacity mode and increase write capacity.

Answer

Enable DynamoDB Accelerator (DAX) to cache write operations.

Question 4

Arrange the steps to set up cross-Region read replicas for an Amazon Aurora MySQL DB cluster in the correct order.

Question 5

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

Question 6

Match each AWS database-related CLI command to its function.

Question 7

Match each backup/restore concept to its AWS database feature.

Question 8

A company is running an Amazon RDS for MySQL Multi-AZ DB instance. They notice that the application is experiencing increased latency during peak hours. The DB instance's CPU utilization is consistently above 80%, and the Read Latency metric is high. Which action would most effectively reduce the latency without requiring application changes?

Accepted Answer

Create a read replica and direct read queries to it.. Option D is correct because Multi-AZ deployments with read replicas offload read traffic and reduce latency. Option A is wrong because increasing instance size may help but does not specifically address read latency. Option B is wrong because enabling Multi-AZ alone does not reduce read latency. Option C is wrong because disabling Multi-AZ would remove the standby, reducing availability.

Answer

Disable Multi-AZ to free up resources.

Answer

Increase the DB instance class to a larger size.

Answer

Enable Multi-AZ on the DB instance.

Question 9

A team is using Amazon DynamoDB with auto scaling enabled. They notice that some requests are returning ProvisionedThroughputExceededException errors during a sudden traffic spike. The application uses strong consistent reads. Which two actions would help mitigate the throttling without over-provisioning capacity? (Choose two.)

Accepted Answer

Implement DynamoDB Accelerator (DAX) to cache read results.. Option A and D are correct. Using DynamoDB Accelerator (DAX) reduces read load, and enabling adaptive capacity helps handle uneven access patterns. Option B is wrong because disabling auto scaling would worsen the issue. Option C is wrong because eventual reads may not be acceptable. Option E is wrong because bursting is limited and not guaranteed.

Answer

Switch to eventually consistent reads for all queries.

Answer

Disable auto scaling and manually set higher capacity.

Answer

Use DynamoDB burst capacity for the spike.

Question 10

A developer is troubleshooting a slow-running query on an Amazon RDS for PostgreSQL instance. The query is performing a sequential scan on a large table. Which AWS service or feature should the developer use to identify the missing index?

Accepted Answer

Amazon RDS Performance Insights. Option B is correct because Performance Insights provides database performance analysis and can identify missing indexes. Option A is wrong because RDS Enhanced Monitoring provides OS-level metrics. Option C is wrong because CloudWatch Logs are for application logs. Option D is wrong because AWS CloudTrail logs API calls.

Answer

Amazon RDS Enhanced Monitoring

Answer

AWS CloudTrail

Answer

Amazon CloudWatch Logs

Question 11

A company uses Amazon ElastiCache for Redis as a caching layer for a web application. They observe a sudden increase in CPU utilization on the cache cluster, and the application experiences higher latency. Which action should be taken to diagnose the issue?

Accepted Answer

Monitor Amazon CloudWatch metrics for the ElastiCache cluster to identify the cause.. Option A is correct because CloudWatch metrics like CPUUtilization and CacheHits are the first step to diagnose. Option B is wrong because increasing node size is a solution, not a diagnostic step. Option C is wrong because ElastiCache does not have a built-in query profiler. Option D is wrong because disabling persistence is unrelated.

Answer

Enable query profiling on the ElastiCache cluster.

Answer

Disable persistence to reduce CPU overhead.

Answer

Immediately scale up to a larger node type.

Question 12

A company runs an Amazon Aurora MySQL database cluster with one writer and two readers. The application suddenly fails with 'Too many connections' error. The writer instance's maximum connections is set to 1000. Which configuration change would best resolve the issue while maintaining high availability?

Accepted Answer

Enable Amazon RDS Proxy for the database cluster.. Option D is correct because a multi-threaded application may exhaust connections; using a connection pooler like RDS Proxy reduces connection churn. Option A is wrong because increasing max_connections may overload the instance. Option B is wrong because read replicas do not accept writes. Option C is wrong because it's not a configuration change.

Answer

Increase the max_connections parameter on the writer instance to 5000.

Answer

Redirect all write requests to one of the read replicas.

Answer

Manually kill idle connections from the database.

Question 13

A developer is troubleshooting an application that is unable to write to a DynamoDB table. The above IAM policy is attached to the IAM role used by the application. What is the likely cause?

Accepted Answer

The Deny statement overrides the Allow statement, blocking all DynamoDB actions.. Option B is correct because the Deny statement for all DynamoDB actions overrides the Allow for PutItem. Deny statements always take precedence. Option A is wrong because the table name is correct. Option C is wrong because the role is assumed. Option D is wrong because the user exists.

Answer

The table name in the Resource ARN is incorrect.

Answer

The IAM user does not exist.

Answer

The role is not correctly assumed by the application.

Question 14

A company uses Amazon DynamoDB with global tables. They notice that changes made in one region are not appearing in another region after several minutes. Which CloudWatch metric should be monitored to check the replication lag?

Accepted Answer

ReplicationLatency. Option C is correct because ReplicationLatency measures the time between the last update on the source table and the last update on the replica table. Option A is wrong because ThrottledRequests indicates throttling. Option B is wrong because ConsumedWriteCapacityUnits measures usage. Option D is wrong because SuccessfulRequestLatency measures request latency.

Answer

ConsumedWriteCapacityUnits

Answer

SuccessfulRequestLatency

Answer

ThrottledRequests

Question 15

A team is troubleshooting an Amazon RDS for SQL Server instance that is running out of storage. The instance uses General Purpose SSD (gp2) storage. The team wants to increase storage without downtime. Which action should they take?

Accepted Answer

Modify the DB instance to increase allocated storage.. Option D is correct because RDS supports modifying storage settings without downtime, and the change occurs during the next maintenance window. Option A is wrong because creating a snapshot does not increase storage. Option B is wrong because gp3 is not supported for SQL Server. Option C is wrong because read replicas do not increase storage on the primary.

Answer

Migrate to gp3 storage.

Answer

Add a read replica to offload queries.

Answer

Take a snapshot and restore to a larger instance.