DBS-C01 Monitoring and Troubleshooting Practice Test 5 — 15 Questions

Question 1

Refer to the exhibit. A database administrator retrieves CloudWatch metrics for an RDS instance. What is the trend of CPU utilization during the monitored period?

Accepted Answer

CPU utilization is increasing over time.. The average CPU utilization increases from 75.5% to 98.2% over the hour, indicating a steady increase. Option A is incorrect because it is not decreasing. Option B is incorrect because it is not constant around 90%. Option C is incorrect because it does not fluctuate randomly; it increases monotonically.

Answer

CPU utilization is decreasing over time.

Answer

CPU utilization is constant around 90%.

Answer

CPU utilization fluctuates randomly.

Question 2

A company is running a production Amazon RDS for MySQL DB instance. The application team reports intermittent high latency and connection timeouts. A quick check shows that the DB instance's CPU utilization is consistently above 90% during peak hours. The database size is 500 GB and the instance class is db.r5.large. Which combination of actions should a database specialist take to resolve the performance issue?

Accepted Answer

Scale up the DB instance to db.r5.xlarge and review slow query logs to optimize poorly performing queries.. Scaling up the DB instance to db.r5.xlarge provides more compute capacity, directly addressing high CPU utilization. Additionally, reviewing slow query logs helps identify and optimize inefficient queries that may be causing CPU spikes. Option A is incorrect because increasing storage does not improve CPU performance; it only addresses storage capacity or I/O issues. Option C is incorrect because enabling Multi-AZ provides high availability but does not increase compute capacity, and increasing storage does not help with CPU. Option D is incorrect because Performance Insights helps diagnose performance issues but does not resolve them, and CloudWatch alarms only provide notifications without fixing the underlying problem.

Answer

Increase the allocated storage to 1 TB and enable auto-scaling for storage.

Answer

Enable Multi-AZ and increase the allocated storage to 1 TB to improve I/O performance.

Answer

Enable Performance Insights and create a CloudWatch alarm to notify when CPU exceeds 80%.

Question 3

A database specialist is troubleshooting a degraded Amazon Aurora MySQL database cluster. The primary instance is showing elevated read latency and the replica lag is increasing. The DB cluster has one writer and one reader instance. The writer instance is using 90% of its allocated memory, and the reader instance is using 70%. Which action is most likely to reduce read latency and replica lag?

Accepted Answer

Increase the reader instance size to provide more buffer pool memory.. Increasing the reader instance size provides more memory for the buffer pool, which improves read performance and can reduce replica lag. The reader is using 70% memory, so adding more buffer pool memory allows it to cache more data and handle read requests faster. Option A is incorrect because increasing storage improves I/O throughput but does not directly address memory constraints or replica lag. Option B is incorrect because the writer instance is already under memory pressure, but the issue is read latency on the reader, not write performance. Option D is incorrect because adding a second reader distributes the read load but does not resolve the memory bottleneck on the existing reader; a larger instance is more effective in this scenario.

Answer

Increase the allocated storage for the cluster to improve I/O throughput.

Answer

Increase the writer instance size to provide more memory for write operations.

Answer

Add a second reader instance to distribute the read load.

Question 4

A company is using Amazon DynamoDB for a gaming leaderboard application. Recently, users have experienced increased latency when updating scores. The DynamoDB table has on-demand capacity mode. The application performs UpdateItem calls with a condition expression. Which action is most likely to reduce the latency?

Accepted Answer

Ensure that there are no throttled requests in the CloudWatch metrics and verify that the table is not experiencing hot partitions.. Increased latency in DynamoDB can be caused by hot partitions where many requests hit the same partition, leading to throttling even with on-demand capacity if the partition limits are exceeded. Checking CloudWatch metrics for throttled requests and partition metrics helps identify hot partitions. Option A is incorrect because adding a GSI does not improve UpdateItem performance; it only helps query performance. Option B is incorrect: on-demand mode already handles capacity, and increasing read capacity units does not affect write operations like UpdateItem. Option C is incorrect: disabling conditional writes would break the application's concurrency control and does not guarantee latency reduction; condition evaluation is a fast, internal operation.

Answer

Add a global secondary index (GSI) with the score as the sort key to improve update performance.

Answer

Switch the table to provisioned capacity and increase the read capacity units to handle peak load.

Answer

Disable conditional writes to reduce the overhead of condition expression evaluation.

Question 5

A database specialist is investigating a sudden increase in Amazon RDS for PostgreSQL connections. The DB instance's CloudWatch metric DatabaseConnections shows a spike from 100 to 500 within minutes. The application connects using a connection pool. Which step should the specialist take first to mitigate the issue while preserving application availability?

Accepted Answer

Modify the DB parameter group to reduce the max_connections value and reboot the instance to apply changes.. Reducing the max_connections value in the DB parameter group and rebooting the instance will limit the number of concurrent connections, preventing the database from being overwhelmed. This is the fastest way to mitigate the spike while preserving application availability. Option A is wrong because terminating all connections and restarting the database would disrupt the application. Option B is wrong because modifying the security group does not affect the number of connections, only the allowed sources. Option C is wrong because increasing the instance size may take time to provision and does not immediately address the connection spike.

Answer

Use the RDS console to terminate all active connections and then restart the database.

Answer

Modify the security group to restrict inbound traffic to the database.

Answer

Increase the DB instance size to handle more connections.

Question 6

A company is using Amazon ElastiCache for Redis as a caching layer for a web application. The application team reports that cache miss rates have increased significantly, causing higher database load. The Redis cluster has two nodes (one primary, one replica) with the default eviction policy of noeviction. Which action should the database specialist recommend to reduce cache misses?

Accepted Answer

Change the eviction policy to allkeys-lru to allow Redis to evict less recently used keys.. Changing the eviction policy to allkeys-lru allows Redis to evict less recently used keys when memory is full, reducing cache misses. Option A is incorrect because simply increasing memory does not change the eviction policy; with noeviction, writes will fail when memory is full. Option C is incorrect because enabling AOF persistence improves durability but does not affect cache misses. Option D is incorrect because adding read replicas distributes read traffic but does not reduce cache misses if the keys are not in the cache.

Answer

Increase the memory of existing nodes to accommodate more keys.

Answer

Enable AOF persistence to improve cache durability.

Answer

Add more read replicas to distribute the cache load.

Question 7

A database specialist needs to monitor the number of deadlocks occurring in an Amazon RDS for SQL Server DB instance. Which CloudWatch metric should be used?

Accepted Answer

Deadlocks. The 'Deadlocks' metric in Amazon RDS for SQL Server specifically counts the number of deadlocks that occur on the DB instance. Option A is incorrect because 'BlockedTransactions' tracks transactions that are blocked, not deadlocks. Option C is incorrect because 'DatabaseConnections' is a count of active connections, not related to deadlocks. Option D is incorrect because 'LockWaits' measures the number of lock waits, which is a different contention event.

Answer

BlockedTransactions

Answer

DatabaseConnections

Answer

LockWaits

Question 8

A company is using Amazon DocumentDB (with MongoDB compatibility) for a content management system. The application team notices that write operations are taking longer than usual. CloudWatch metrics show high WriteLatency and a growing number of documents in the oplog. Which step should the database specialist take to troubleshoot the issue?

Accepted Answer

Check the CPU and memory utilization of the secondary instance and consider scaling it up.. High WriteLatency and growing oplog suggest that the secondary instance is too slow to apply operations, causing replication lag. Checking the secondary's metrics helps diagnose. Option A is wrong because enabling Multi-AZ does not directly address write latency. Option B is wrong because increasing the instance class may help but should be done after diagnosis. Option C is wrong because increasing storage does not improve write performance.

Answer

Enable Multi-AZ on the cluster to offload reads to the standby.

Answer

Increase the instance size of the primary instance to handle more writes.

Answer

Increase the allocated storage to improve I/O throughput.

Question 9

A company is using Amazon Redshift for data warehousing. The data engineering team notices that queries are taking longer than expected. The cluster has two nodes of type dc2.large. The database specialist checks the system tables and finds that many queries are using the disk for temporary storage. Which action should the specialist take to improve query performance?

Accepted Answer

Upgrade the cluster to a node type with more memory, such as ra3.xlplus.. Disk spill to temporary storage indicates insufficient memory per node. Upgrading from dc2.large (∼15 GB RAM) to ra3.xlplus (∼32 GB RAM) doubles per-node memory, reducing disk spill and improving query performance. Option A is incorrect because distribution keys improve data distribution, not memory. Option B is incorrect because concurrency scaling manages concurrent queries, not per-query memory. Option C is incorrect because adding a node increases total cluster memory but per-node memory stays the same; disk spill occurs per node, so the problem persists.

Answer

Add distribution keys to the tables to improve data distribution.

Answer

Enable concurrency scaling to offload queries to additional clusters.

Answer

Increase the number of nodes to three to distribute the workload.

Question 10

A database specialist is troubleshooting an Amazon RDS for MySQL DB instance that is running out of storage. The instance has automated backups enabled. The specialist needs to free up storage space immediately without losing backup capability. Which action should the specialist take?

Accepted Answer

Delete older automated backups that are no longer needed.. None of the provided options will free up DB instance storage. Automated backups are stored in Amazon S3, not in the instance's allocated storage. To free up instance storage, you would need to increase the allocated storage or delete actual data from the database. Reducing backup retention deletes backups from S3, not instance storage. Manual snapshots are also in S3. Disabling backups stops future backups but does not free existing storage.

Answer

Modify the DB instance to reduce the backup retention period to 0 days.

Answer

Delete manual snapshots from the RDS console.

Answer

Disable automated backups to stop storage consumption.

Question 11

A database specialist is troubleshooting a slow-running query on an Amazon Aurora MySQL DB cluster. The query performs a large table scan. Which THREE actions would likely improve query performance?

Accepted Answer

Increase the size of the DB instance to provide more memory and CPU.. Creating appropriate indexes can speed up queries by avoiding table scans. Increasing the instance size provides more memory and CPU for query execution. Enabling query caching can store results of repeated queries. Changing isolation level and enabling parallel query may not help in all cases and may have side effects.

Answer

Change the transaction isolation level to SERIALIZABLE.

Answer

Enable Aurora Parallel Query to parallelize the table scan.

Question 12

A company is using Amazon DynamoDB for a session management application. The application is experiencing higher latency during peak hours. The DynamoDB table uses on-demand capacity. Which TWO steps should a database specialist take to diagnose the issue?

Accepted Answer

Check the CloudWatch metric for ThrottledRequests to see if any requests are being throttled.. Checking ThrottledRequests helps identify if requests are being throttled, even with on-demand. Reviewing PartitionKey metrics helps detect hot partitions. ReadCapacityUnits and WriteCapacityUnits are not applicable for on-demand. Latency metrics show end-to-end performance but are less diagnostic.

Answer

Review the table's ReadCapacityUnits and WriteCapacityUnits to ensure they are sufficient.

Answer

Examine the CloudWatch metric for UserErrors to identify client-side issues.

Answer

Enable DynamoDB Streams to capture all write events for analysis.

Question 13

Refer to the exhibit. A database specialist is investigating performance degradation on an Amazon RDS for MySQL DB instance. The BurstBalance metric shows the values above. What does this indicate, and what action should be taken?

Accepted Answer

The instance has exhausted its I/O burst credits; scale up the allocated storage to increase baseline I/O.. The BurstBalance metric dropping to 0 indicates that the instance has exhausted its I/O burst credits, resulting in I/O throttling. Scaling up the allocated storage increases the baseline I/O performance, which in turn increases the burst credit earning rate and raises the burst balance. Option B is incorrect because adding a read replica offloads read traffic but does not increase I/O credits. Option C is incorrect because changing the instance class does not affect I/O credits; it only increases compute capacity. Option D is incorrect because enabling Performance Insights helps with diagnosis but does not resolve I/O credit exhaustion.

Answer

The instance is experiencing high read load; add a read replica to offload reads.

Answer

The instance's compute capacity is insufficient; change the instance class to a larger size.

Answer

The instance is experiencing a memory bottleneck; enable Performance Insights to analyze query performance.

Question 14

Refer to the exhibit. A database specialist is troubleshooting an automation script that fails when trying to create a snapshot of the RDS DB instance 'mydb' using an IAM role with the attached policy. The error message indicates that the user is not authorized to perform the operation. Which statement best explains the failure?

Accepted Answer

The policy does not grant the rds:CreateDBSnapshot permission on the DB instance resource.. The rds:CreateDBSnapshot action requires permission on the DB instance resource (arn:aws:rds:region:account:db:instance-name). The IAM policy in the exhibit only grants this action on the snapshot resource (arn:aws:rds:region:account:snapshot:*), not on the DB instance, causing the authorization failure. Options A and B are incorrect because they either mention an irrelevant action or misidentify the resource. Option C is incorrect because the policy does allow rds:CreateDBSnapshot on the snapshot resource, but the missing permission on the DB instance is the actual issue.

Answer

The resource ARN for the snapshot is incorrect; it should specify the DB instance ID.

Answer

The policy does not allow the rds:DescribeDBInstances action on the snapshot resource.

Answer

The policy does not allow the rds:CreateDBSnapshot action on the specific snapshot name.

Question 15

Refer to the exhibit. A database specialist is investigating an application outage that occurred at 14:25 UTC. The RDS event log shows the events above. What is the most likely cause of the outage?

Accepted Answer

A Multi-AZ failover occurred at 14:25 UTC, causing a brief outage.. The RDS event log shows 'Multi-AZ failover completed' at 14:25 UTC, which would cause a brief outage during the DNS switchover. The subsequent restart at 14:30 UTC is likely a result of the failover (e.g., instance recovery). Option A is wrong because there is no event indicating a maintenance window. Option B is wrong because storage-full events would show before the outage, not a failover event. Option D is wrong because a manual reboot would not show a Multi-AZ failover event; the restart at 14:30 is after the failover.

Answer

A maintenance window update was applied, causing the instance to become unavailable.

Answer

The DB instance ran out of storage and became read-only.

Answer

The DB instance restarted at 14:30 UTC due to a manual reboot.