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

Question 1

A company uses Amazon DynamoDB with global tables. During a regional outage, the application fails over to the secondary region. After recovery, the DBA notices that the data in the secondary region is not fully consistent with the primary. Which THREE steps should the DBA take to diagnose the issue? (Choose THREE.)

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

Accepted Answer

Verify that DynamoDB Streams is enabled on the table.. Options A, D, and E are correct. Verifying DynamoDB Streams (A) ensures that change data capture is enabled for replication. Reviewing DynamoDB Streams error logs in CloudWatch Logs (D) helps identify replication errors. Checking the ReplicationLatency metric (E) reveals if there is replication lag. Option B is not a diagnostic step; disabling and re-enabling global tables is disruptive and not recommended. Option C is incorrect because increasing write capacity on the secondary table does not address consistency issues; replication depends on streams and network, not write capacity.

Answer

Disable and re-enable global tables to force resync.

Answer

Increase the write capacity on the secondary table.

Question 2

A company is running a critical Oracle database on Amazon RDS. The DBA wants to set up monitoring to detect if the database is experiencing a high number of full table scans, which may indicate missing indexes. Which TWO metrics should the DBA monitor? (Choose TWO.)

Accepted Answer

TableScanRows. The DBA should monitor TableScanRows (A) and FullTableScans (B). FullTableScans directly counts the number of full table scan operations, while TableScanRows indicates the number of rows read during full scans. High values in either metric suggest missing indexes. BufferCacheHitRatio (C) measures cache efficiency, not full scans. UserCommits (D) tracks transaction commits, and RedoLogSpaceUsage (E) relates to redo log activity, neither of which indicate full table scans.

Answer

BufferCacheHitRatio

Answer

UserCommits

Answer

RedoLogSpaceUsage

Question 3

A company is running an Amazon RDS for PostgreSQL DB instance with Multi-AZ deployment. They notice that the primary DB instance is experiencing high CPU utilization. The read replica shows normal CPU. Which action should the DBA take to reduce the load on the primary instance?

Accepted Answer

Offload SELECT queries to the read replica. Offloading SELECT queries to the read replica reduces CPU utilization on the primary instance because read replicas can handle read traffic independently. Option A is incorrect: failing over to the standby instance does not reduce CPU load—the standby is only for high availability and becomes the new primary, still handling the same workload. Option B is incorrect: increasing the DB instance size would help but is not the best first step; it involves scaling costs and potential downtime, whereas using a read replica is more efficient and cost-effective for read-heavy workloads. Option C is incorrect: converting the read replica to a Multi-AZ standby would make it a synchronous replica for failover, not for offloading reads, so it would not reduce CPU on the primary.

Answer

Failover to the standby instance

Answer

Increase the DB instance size

Answer

Convert the read replica to a Multi-AZ standby

Question 4

A database team uses Amazon DynamoDB with auto scaling enabled. They observe frequent throttling on a table during peak hours. The table's read capacity is set to 5000 RCU with auto scaling range 3000-7000. The consumed read capacity graph shows spikes to 6000 RCU but throttling occurs at 5500. What is the most likely cause?

Accepted Answer

Auto scaling cannot react quickly enough to sudden traffic spikes. Auto scaling uses a target utilization (default 70%) and cannot scale fast enough for sudden spikes. Option A is wrong because auto scaling is enabled. Option B is wrong because WCU are separate. Option C is wrong because partition count doesn't directly cause throttling if RCU is sufficient.

Answer

Write capacity units are insufficient

Answer

Auto scaling is disabled for the table

Answer

The table has too many partitions

Question 5

A developer is troubleshooting a slow query on Amazon RDS for MySQL. The query joins three large tables and runs frequently. What is the most effective way to identify the bottleneck?

Accepted Answer

Enable the slow query log and analyze the output. Enabling the slow query log on RDS for MySQL captures queries that exceed a specified execution time, allowing the developer to identify which queries are slow and analyze their execution plan to find bottlenecks. Option A is wrong because RDS Events are for maintenance and operational notifications, not query performance. Option B is wrong because CloudWatch CPU and memory metrics show overall resource utilization but do not pinpoint specific slow queries. Option D is wrong because migrating to a larger instance may help but does not directly identify the bottleneck; it addresses symptoms rather than root cause analysis.

Answer

Check the RDS Events for any maintenance notifications

Answer

Review Amazon CloudWatch CPU and memory metrics

Answer

Use AWS Database Migration Service to migrate to a larger instance

Question 6

A company uses Amazon ElastiCache for Redis as a caching layer for a web application. They notice increased latency and cache miss rates. The cache cluster has 5 nodes with replication. Which metric should be monitored to identify if the cache is under-provisioned?

Accepted Answer

CPUUtilization. High CPUUtilization indicates the cache nodes are overloaded, suggesting the cache is under-provisioned and cannot handle the request volume. Option A is incorrect because ReplicationLag measures replication delays, not overall capacity. Option B is incorrect because CacheHits measure cache effectiveness, but a high miss rate could be due to capacity or other factors; CPU is more direct for throughput. Option D is incorrect because Evictions occur when memory is full, but CPU utilization is a better indicator of processing capacity constraints.

Answer

ReplicationLag

Answer

CacheHits

Answer

Evictions

Question 7

A company runs an Amazon Aurora MySQL DB cluster with one writer and two readers. They notice that one reader instance is consistently showing higher than expected lag. The other reader is fine. What is the most likely cause?

Accepted Answer

The reader instance is being used for heavy analytical queries. An imbalanced workload on that reader can cause it to lag. Option A is wrong because writer load affects all replicas. Option B is wrong because network issues would affect both readers. Option D is wrong because parameter group change would affect both readers if applied to cluster.

Answer

The writer instance is experiencing high write activity

Answer

There is a network connectivity issue between the writer and that reader

Answer

The reader instance has a different DB parameter group

Question 8

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. Amazon RDS Performance Insights provides real-time information about active database connections and sessions. Option A (AWS Trusted Advisor) is incorrect because it offers best practice recommendations, not connection monitoring. Option B (VPC Flow Logs) is incorrect because they capture network traffic metadata, not database-level connection details. Option D (AWS CloudTrail) is incorrect because it records API calls for auditing, not real-time database connections.

Answer

AWS Trusted Advisor

Answer

VPC Flow Logs

Answer

AWS CloudTrail

Question 9

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. Increasing the instance size of the target RDS instance provides more CPU and memory resources for the CDC process, allowing it to process more changes per unit time and catch up on lag. Option A is incorrect because disabling supplemental logging on the source Oracle database would prevent the capture of necessary change data, breaking CDC entirely and preventing any catch-up. Option C is incorrect because pausing the CDC task would stop processing changes, allowing the lag to grow further, not catch up. Option D is incorrect because stopping CDC and performing a full load migration would cause significant downtime, which contradicts the requirement for minimal downtime.

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 10

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. Creating appropriate indexes on the fields used in query filters is the most effective action to improve performance because it eliminates the need for a COLLSCAN (collection scan). Increasing instance size (option A) may help but does not address the root cause of missing indexes. Changing read consistency from eventual to strong (option B) affects the freshness of reads, not query performance. Increasing storage (option C) does not improve query speed; it only provides more space for data.

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 11

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. The ReplicationLatency metric in CloudWatch directly measures the delay between a write in one region and its replication to another region in DynamoDB global tables. This is the most relevant metric to diagnose replication delays. Option B (auto scaling) affects capacity provisioning, not replication timing. Option C (DynamoDB Streams) are enabled by default for global tables to facilitate replication, but checking the metric is the immediate next step if delays are observed. Option D (table size) does not directly cause replication delays; replication is asynchronous and not size-dependent.

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 12

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

Accepted Answer

SwapUsage. A and D are correct. SwapUsage directly indicates memory pressure when it exceeds 0, as the operating system swaps memory to disk. FreeableMemory shows the amount of available memory, so a low value suggests memory pressure. B (DatabaseConnections) is incorrect because it is an indirect indicator that can affect memory but is not a direct memory metric. C (ReadIOPS) is disk I/O, not memory. E (CPUUtilization) is CPU usage, not memory.

Answer

DatabaseConnections

Answer

ReadIOPS

Answer

CPUUtilization

Question 13

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 14

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

Accepted Answer

Amazon RDS Performance Insights. A is correct: Amazon RDS Performance Insights provides a visualization of database performance, including metrics like average active sessions, which helps identify query performance issues. C is correct: Amazon RDS Enhanced Monitoring provides OS-level metrics such as CPU, memory, and disk I/O, which can help correlate with query performance. B is incorrect: AWS Config is a service for configuration audit and compliance, not for real-time performance monitoring. D is incorrect: VPC Flow Logs capture network traffic metadata and are not specific to query performance. E is incorrect: AWS CloudTrail logs API calls for governance and compliance, not database query performance.

Answer

AWS Config

Answer

VPC Flow Logs

Answer

AWS CloudTrail

Question 15

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. The IAM policy includes an explicit Deny statement that specifically denies the DeleteDBInstance action on the production-db instance. In IAM, an explicit Deny overrides any Allow, so even if other statements allow DeleteDBInstance, this Deny prevents the deletion. Option B is incorrect because the policy does allow DeleteDBInstance on other resources, so the issue is not a lack of general permissions. Option C is incorrect because the policy includes Allow on DescribeDBInstances. Option D is incorrect because the policy does not restrict CreateDBInstance; the problem is specific to deletion of production-db.

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