DBS-C01 Monitoring and Troubleshooting Practice Test 8 — 15 Questions

Question 1

An administrator notices that the CloudWatch metric 'ReadLatency' for an Amazon RDS for SQL Server instance has increased significantly. Which of the following is the most likely cause?

Accepted Answer

The DB instance does not have enough provisioned IOPS.. High ReadLatency indicates that read operations are taking longer than expected. This is most directly caused by insufficient I/O throughput, i.e., not enough provisioned IOPS for the workload. When the database requests more IOPS than are provisioned, I/O operations queue up, increasing latency. Option D is correct because insufficient provisioned IOPS is a primary cause of increased ReadLatency. Option A is incorrect: high CPU utilization can affect overall performance but does not directly cause read latency unless it leads to I/O contention. Option B is incorrect: running out of memory can cause disk swapping, which may increase latency, but it is less direct than I/O throttling. Option C is incorrect: burstable instance classes (like T-series) use CPU credits; exhaustion affects CPU performance, not storage I/O latency.

Answer

The DB instance is experiencing high CPU utilization.

Answer

The DB instance is running out of memory.

Answer

The DB instance is using a burstable instance class that has exhausted its credits.

Question 2

A company is using Amazon DynamoDB with auto scaling enabled. The application is experiencing higher than expected write throttling. Which action should be taken to resolve this issue?

Accepted Answer

Increase the minimum provisioned capacity for the table.. Auto scaling adjusts capacity based on workload, but it can lag behind sudden traffic spikes, causing write throttling. Increasing the minimum provisioned capacity ensures a baseline capacity that can accommodate predictable bursts, reducing throttling. Option A (increase min capacity) is correct. Option B (disable auto scaling and set fixed capacity) would remove the benefit of dynamic scaling and may not handle varying loads. Option C (decrease max capacity) would limit the table's ability to scale up, potentially worsening throttling. Option D (switch to on-demand) could eliminate throttling but at higher cost, and the question asks for a resolution while keeping auto scaling enabled.

Answer

Disable auto scaling and set a fixed provisioned capacity.

Answer

Decrease the maximum provisioned capacity to limit writes.

Answer

Switch the table to on-demand capacity mode.

Question 3

A company has an Amazon Aurora MySQL DB cluster with one writer and two readers. The application is reporting increased read latency. The DB cluster is using Aurora Auto Scaling for readers. Which metric should be used to trigger scaling out readers?

Accepted Answer

AverageActiveConnections. Aurora Auto Scaling for readers uses the 'AverageActiveConnections' metric to determine when to add readers. Option D is correct. Option A is incorrect because average active connections is the trigger, not read latency. Option B is incorrect because ReaderNodeCPU is not a predefined metric for auto scaling. Option C is incorrect because CPUUtilization is not the metric used for reader scaling.

Answer

ReadLatency

Answer

ReaderNodeCPU

Answer

CPUUtilization

Question 4

A company is using Amazon DynamoDB with a global table in two regions. The application is experiencing high write latency on the replica table in the secondary region. Which THREE factors could contribute to this issue?

Accepted Answer

Large item sizes being written to the table.. Global tables replicate writes asynchronously. Large item sizes (A) increase the time to process each write. Network latency (B) between regions affects the replication time. Insufficient write capacity (E) on the replica table can cause throttling and increased latency. Auto scaling configuration (C) is not a direct cause; it helps manage capacity. Read capacity (D) does not affect write latency.

Answer

Auto scaling configuration on the replica table.

Answer

Low read capacity on the replica table.

Question 5

An Amazon RDS for MySQL instance is running out of storage. Which TWO actions can be taken to resolve this issue without downtime?

Accepted Answer

Enable storage auto scaling to automatically add storage.. Amazon RDS for MySQL supports modifying storage to increase allocated storage without downtime (option C). You can also enable storage auto scaling to automatically increase storage when thresholds are met (option A). Deleting unnecessary data (option B) might free space but is not a reliable proactive measure and could involve manual effort. Taking a snapshot and restoring to a larger instance (option D) requires downtime. Converting to Amazon Aurora (option E) is a migration process, not a direct fix for running out of storage.

Answer

Delete unnecessary data from the instance.

Answer

Take a snapshot and restore to a larger instance.

Answer

Convert the instance to Amazon Aurora.

Question 6

A database administrator notices that an Amazon RDS for MySQL DB instance's CPU utilization is consistently above 90% during peak hours. Which initial troubleshooting step should the administrator take?

Accepted Answer

Use Amazon RDS Performance Insights to identify the queries consuming CPU.. Amazon RDS Performance Insights provides detailed database performance metrics and helps identify the specific queries contributing to high CPU utilization, enabling targeted optimization. Option A is incorrect because increasing instance size is a reactive scaling action rather than a diagnostic step; it does not identify the root cause. Option C is incorrect because Multi-AZ deployment is designed for high availability and failover, not for distributing load or improving performance. Option D is incorrect because disabling slow query logging removes valuable diagnostic information that could help identify problematic queries.

Answer

Increase the DB instance size to handle the load.

Answer

Enable Multi-AZ deployment to distribute the load.

Answer

Disable slow query logging to reduce CPU overhead.

Question 7

A company uses Amazon DynamoDB with on-demand capacity. Users report increased latency during peak hours. The application uses the DynamoDB API. Which monitoring metric should be examined first to identify throttling issues?

Accepted Answer

ThrottledRequests. (ThrottledRequests). ThrottledRequests is a CloudWatch metric that directly indicates the number of requests that were throttled due to exceeding provisioned throughput limits or the instantaneous capacity of on-demand mode. For on-demand capacity, while DynamoDB scales automatically, sudden spikes can still cause throttling. Examining ThrottledRequests first provides the most direct indication of throttling issues. Option B (SuccessfulRequestLatency) is incorrect because it measures latency of successful requests, not throttling. Option C (ReadThrottleEvents) is incorrect because it only counts throttled read events, whereas ThrottledRequests includes both reads and writes. Option D (ConsumedWriteCapacityUnits) is incorrect because it shows the amount of write capacity consumed, not throttled requests.

Answer

SuccessfulRequestLatency

Answer

ReadThrottleEvents

Answer

ConsumedWriteCapacityUnits

Question 8

An e-commerce application uses Amazon Aurora MySQL. During a flash sale, the database experiences a surge in write operations, and the application reports 'Lock wait timeout exceeded' errors. The DBA suspects a long-running transaction is blocking others. Which AWS tool or feature should the DBA use to identify the blocking transaction?

Accepted Answer

Amazon Aurora Performance Insights with the 'Wait for lock' dimension. Amazon Aurora Performance Insights with the 'Wait for lock' dimension can identify blocking sessions by showing which sessions are waiting on locks and which session holds the lock. Option B (Amazon Inspector) is a security assessment tool and does not provide database lock information. Option C (CloudWatch Logs Insights) can analyze logs but does not directly identify blocking transactions. Option D (Amazon RDS Enhanced Monitoring) provides OS-level metrics, not database-level lock information.

Answer

Amazon Inspector

Answer

CloudWatch Logs Insights

Answer

Amazon RDS Enhanced Monitoring

Question 9

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. After migration, the application team reports that queries are slower than before. Which metric in CloudWatch should the DBA review first to check if the instance is resource-constrained?

Accepted Answer

CPUUtilization. (CPUUtilization). When migrating an on-premises Oracle database to Amazon RDS for Oracle, slower queries can indicate resource constraints. CPUUtilization is the primary metric to review first because high CPU usage directly impacts query performance. Option A (SwapUsage) is more relevant for memory pressure but not the first indicator. Option C (FreeableMemory) is important but CPU is typically the first bottleneck. Option D (DatabaseConnections) shows concurrent connections but does not directly measure resource saturation.

Answer

SwapUsage

Answer

FreeableMemory

Answer

DatabaseConnections

Question 10

A gaming company uses Amazon DynamoDB with provisioned capacity. During a new game launch, the read activity spikes and some requests receive 'ProvisionedThroughputExceededException' errors. The operations team needs to monitor read throttling in real-time. Which CloudWatch metric should they create an alarm for?

Accepted Answer

ReadThrottleEvents. (ReadThrottleEvents) because this metric directly counts the number of read requests that are throttled due to exceeding provisioned read capacity. Option B (ConsumedReadCapacityUnits) shows the amount of read capacity used, not throttled events. Option D (ThrottledRequests) includes both read and write throttles, so it is not specific to reads. Option A (ReadLatency) measures response time, not throttling.

Answer

ReadLatency

Answer

ConsumedReadCapacityUnits

Answer

ThrottledRequests

Question 11

A financial services company runs a critical PostgreSQL database on Amazon RDS. The DBA needs to ensure that any database failover is detected within 30 seconds. Which monitoring approach should be used to meet this requirement?

Accepted Answer

Subscribe to RDS Event Notifications and create an SNS topic for 'failover' events.. Amazon RDS Event Notifications for 'failover' events are delivered within seconds, meeting the 30-second requirement. Subscribing to SNS topics ensures near real-time notification. Option B is wrong because the 'DatabaseConnections' metric with a 1-minute evaluation period introduces a delay of up to 1 minute, exceeding the 30-second threshold. Option C is wrong because Enhanced Monitoring provides OS-level metrics every second but does not directly indicate a failover event. Option D is wrong because CloudTrail logs API calls with a typical delay of several minutes, not suitable for sub-minute detection.

Answer

Create a CloudWatch alarm on the 'DatabaseConnections' metric with a 1-minute evaluation period.

Answer

Use Enhanced Monitoring to monitor the 'engine' process status every second.

Answer

Enable CloudTrail and monitor the 'FailoverDBCluster' API call.

Question 12

A startup uses Amazon ElastiCache for Redis as a caching layer for its database. Users report that application responses are slow. The developer checks the ElastiCache metrics and sees that 'CacheHits' are low and 'CacheMisses' are high. What is the most likely cause?

Accepted Answer

The cache key TTL is too short, causing frequent evictions.. A low cache hit ratio and high cache miss ratio indicate that the cache is not storing data that is frequently requested. The most likely cause is that the Time-To-Live (TTL) for cache keys is set too short, causing data to be evicted before it can be reused. Option A is incorrect because read replicas improve read scalability but do not directly affect cache hit ratio. Option B is incorrect because write capacity is not relevant for a caching layer that primarily serves reads. Option C is incorrect: while high CPU utilization can cause latency, it would not specifically cause low cache hits and high misses.

Answer

The cluster does not have enough read replicas.

Answer

The ElastiCache cluster does not have enough write capacity.

Answer

The ElastiCache nodes have high CPU utilization.

Question 13

A company is using Amazon RDS for SQL Server with Multi-AZ. The application experiences a brief interruption during a planned maintenance window. The DBA wants to verify that the failover occurred correctly. Which set of metrics should the DBA examine?

Accepted Answer

DatabaseConnections and ReplicaLag. During a Multi-AZ failover, DatabaseConnections drop to zero as existing connections are terminated, then rise again as applications reconnect. ReplicaLag, which measures the delay between primary and standby, becomes zero after failover because the former standby is now the primary. Monitoring these two metrics together provides clear evidence of a failover event. Option A (FreeStorageSpace) does not change during failover. Option C (WriteIOPS and ReadIOPS) may fluctuate but are not direct indicators of failover. Option D (NetworkThroughput) may also vary but is not a specific failover indicator.

Answer

FreeStorageSpace on the primary instance

Answer

WriteIOPS and ReadIOPS for both instances

Answer

NetworkThroughput on the replica instance

Question 14

A data analytics company runs Amazon Redshift clusters. A user reports that a complex query is taking much longer than expected. The DBA uses the STL_QUERY view to check the query execution. Which column in STL_QUERY should the DBA examine to identify if the query is waiting for resources?

Accepted Answer

service_class. The 'service_class' column indicates the workload management (WLM) queue assigned to the query, which can help identify if the query was queued or waiting for resources. Option A is wrong because 'aborted' indicates whether the query was aborted, not waiting. Option B is wrong because 'query' is just the query ID. Option C is wrong because 'starttime' shows when the query started, not waiting status.

Answer

aborted

Answer

query

Answer

starttime

Question 15

A database team is troubleshooting a performance issue on an Amazon RDS for PostgreSQL instance. They notice that the 'DiskQueueDepth' metric is consistently high. Which TWO actions should the team take to resolve this issue? (Choose TWO.)

Accepted Answer

Enable storage auto scaling.. Options B and C are correct. A high disk queue depth indicates an I/O bottleneck on the RDS instance. Enabling storage auto scaling (B) allows the storage to automatically scale up when I/O demand increases, which can reduce queue depth. Increasing provisioned IOPS (C) directly improves the I/O performance by providing more throughput. Option A is incorrect because increasing connections can increase I/O contention, not reduce it. Option D is incorrect because PostgreSQL does not support query caching in the same way as MySQL, and it is not a solution to an I/O bottleneck. Option E is incorrect because Multi-AZ provides high availability but does not directly improve I/O performance.

Answer

Increase the number of database connections.

Answer

Enable query caching in PostgreSQL.

Answer

Enable Multi-AZ deployment.