DBS-C01 Monitoring and Troubleshooting Practice Test 14 — 15 Questions

Question 1

A company is running an Amazon DynamoDB table with on-demand capacity. The application is experiencing high latency for GetItem operations. CloudWatch shows that 'ThrottledRequests' is zero, but 'ConsumedReadCapacityUnits' is consistently below the provisioned limit. The table has a global secondary index (GSI) with a different partition key. What is the most likely cause of the high latency?

Accepted Answer

Throttling on the global secondary index due to uneven access patterns. Option D is correct because GSIs have their own capacity and if the GSI is throttled, writes to the base table can be throttled, affecting read latency. Option A is wrong because throttled requests are zero. Option B is wrong because on-demand capacity does not have a provisioned limit. Option C is wrong because hot partitions would cause throttling.

Answer

High write activity on the base table causing read latency

Answer

Insufficient provisioned read capacity on the base table

Answer

Throttling on the base table due to hot partitions

Question 2

A company's Amazon RDS for MySQL DB instance is experiencing high CPU utilization. The DB instance is a db.r5.large with 200 GB of General Purpose SSD (gp2) storage. The application is performing many complex queries. Which action would BEST reduce CPU utilization without changing the application code?

Accepted Answer

Scale up the DB instance to db.r5.xlarge. Option A is correct because scaling up the instance provides more CPU capacity. Option B is wrong because read replicas help with read scaling but not CPU on the writer. Option C is wrong because gp3 storage does not affect CPU. Option D is wrong because changing the query cache is unlikely to significantly reduce CPU.

Answer

Create a read replica and route write queries to it

Answer

Modify the storage type to gp3

Answer

Enable the query cache parameter

Question 3

A company is using Amazon Redshift for data warehousing. The data engineering team notices that queries are running slower than expected. CloudWatch shows that 'CPUUtilization' is high and 'DiskSpaceUsage' is also high. The cluster has 4 dc2.large nodes. What is the most likely cause of the performance degradation?

Accepted Answer

Queries are spilling to disk due to insufficient memory. Option B is correct because high disk usage on dc2 nodes indicates that the cluster is spilling to disk due to insufficient memory. Option A is wrong because network throughput is not indicated. Option C is wrong because WLM queue waits would show in other metrics. Option D is wrong because high CPU alone does not explain disk usage.

Answer

Insufficient network bandwidth between nodes

Answer

CPU is the bottleneck and needs more compute nodes

Answer

Workload management (WLM) queue is causing query waits

Question 4

A company is running an Amazon DynamoDB table with provisioned capacity. The table has a partition key of 'user_id' and a sort key of 'timestamp'. The application performs frequent Query operations using the partition key and a range of sort keys. Recently, the 'ThrottledRequests' metric has spiked. The read and write capacity units are consistently at 80% utilization. What is the most effective way to resolve the throttling?

Accepted Answer

Enable DynamoDB Auto Scaling with a higher target utilization. Option D is correct because using an adaptive capacity add-on allows DynamoDB to automatically manage throughput for hot partitions. Option A is wrong because increasing capacity units may not help if throttling is due to hot partitions. Option B is wrong because GSI does not directly solve hot partition throttling. Option C is wrong because changing partition key distribution would require table redesign and data migration.

Answer

Increase the provisioned read and write capacity units

Answer

Add a global secondary index with a different partition key

Answer

Change the partition key to a more uniformly distributed attribute

Question 5

A company is using Amazon RDS for PostgreSQL and needs to monitor the database for performance issues. Which TWO metrics in Amazon CloudWatch are most useful for identifying I/O bottlenecks?

Accepted Answer

ReadIOPS. Option B is correct because ReadIOPS and WriteIOPS show the actual I/O operations. Option D is correct because DiskQueueDepth indicates pending I/O requests, which suggests contention. Option A is wrong because CPU utilization is compute, not I/O. Option C is wrong because FreeStorageSpace is capacity, not performance. Option E is wrong because DatabaseConnections is about connections, not I/O.

Answer

FreeStorageSpace

Answer

DatabaseConnections

Answer

CPUUtilization

Question 6

A company's Amazon Aurora MySQL DB cluster is experiencing a failover event. Which THREE metrics in CloudWatch should be examined to understand the cause of the failover?

Accepted Answer

ACUUtilization. Option A is correct because FailoverCount shows how many failovers occurred. Option B is correct because DatabaseConnections can indicate if connections were dropped or maxed out. Option D is correct because ACUUtilization can show resource exhaustion that may trigger failover. Option C is wrong because BinLogDiskUsage is about binary logs, not failover cause. Option E is wrong because ReadLatency is a symptom but not a direct cause of failover.

Answer

ReadLatency

Answer

BinLogDiskUsage

Question 7

A company is troubleshooting an Amazon DynamoDB table that is experiencing high latency. The table uses on-demand capacity. Which TWO steps should be taken to diagnose the issue?

Accepted Answer

Examine CloudWatch metrics for throttling and latency patterns. Option A is correct because CloudWatch metrics can show throttling, latency, and utilization. Option D is correct because DynamoDB Accelerator (DAX) can reduce latency if the issue is high read volume. Option B is wrong because increasing capacity is not needed for on-demand. Option C is wrong because partitions are managed automatically. Option E is wrong because disabling TTL is unrelated.

Answer

Increase the provisioned read capacity

Answer

Disable TTL to reduce write overhead

Answer

Split the table into multiple partitions manually

Question 8

A company's Amazon Redshift cluster is experiencing slow query performance. Which THREE diagnostic steps should be taken to identify the bottleneck?

Accepted Answer

Query SVL_QUERY_REPORT to see step-level performance. Option A is correct because STL_QUERY provides query execution details. Option C is correct because SVL_QUERY_REPORT shows step-level execution. Option E is correct because STL_WLM_QUERY shows WLM queue waits. Option B is wrong because STV_BLOCKLIST shows disk allocation, not performance. Option D is wrong because STL_LOAD_ERRORS is for load errors.

Answer

Query STL_LOAD_ERRORS to check for data load errors

Answer

Query STV_BLOCKLIST to check disk allocation

Question 9

A company is experiencing slow query performance on an Amazon RDS for PostgreSQL DB instance. The DB instance is a db.r5.large with 16 GB RAM and 500 GB gp2 storage. Which metric in Amazon CloudWatch would most directly help identify if the performance issue is due to memory pressure?

Accepted Answer

Monitor FreeableMemory to see if available memory is low.. FreeableMemory shows the amount of available RAM. Low FreeableMemory indicates memory pressure, which can cause swapping and slow queries. Option A is wrong because CPUUtilization measures CPU, not memory. Option B is wrong because DatabaseConnections tracks connections, not memory. Option C is wrong because ReadIOPS measures I/O operations, not memory.

Answer

Monitor ReadIOPS to see if there is a high I/O rate due to swapping.

Answer

Monitor DatabaseConnections to check for a high number of connections consuming memory.

Answer

Monitor CPUUtilization to check for high CPU usage.

Question 10

A developer reports that an application is unable to connect to an Amazon RDS for MySQL DB instance. The security group for the DB instance allows inbound traffic on port 3306 from the application server's security group. The DB instance is in a VPC with both public and private subnets. The application server is in a private subnet. What is the most likely cause of the connection failure?

Accepted Answer

The security group for the DB instance does not allow inbound traffic from the application server's security group.. If the DB instance is in a public subnet and the application server is in a private subnet, they are in different subnets within the same VPC, so they can communicate via private IPs if routing is correct. However, the most common issue is that the security group rule is not correctly associated or the DB instance is in a public subnet with a public DNS name that resolves to a public IP, but the private subnet cannot reach the internet. But the question implies the DB instance is in a public subnet; private subnet instances can reach public subnet instances via the VPC router. However, often the misconfiguration is that the DB instance's security group does not allow traffic from the application server's security group. Option D is correct because the security group rule might be missing or incorrect. Option A is wrong because NACLs are stateless and typically allow all outbound. Option B is wrong because the DB instance is in a public subnet, but the application server is in a private subnet, they can communicate within the VPC. Option C is wrong because the DB subnet group is for Multi-AZ, not single instance.

Answer

The DB instance is in a public subnet and the application server is in a private subnet, so they cannot communicate.

Answer

The network ACL for the private subnet is blocking outbound traffic to the DB instance.

Answer

The DB instance is not part of a DB subnet group that includes the private subnet.

Question 11

A company uses Amazon DynamoDB with auto scaling enabled. The application experiences increased latency during peak hours. The DynamoDB table has a read capacity of 10,000 RCU and write capacity of 5,000 WCU. The auto scaling target utilization is 70%. During peak hours, the consumed read capacity reaches 8,000 RCU, but auto scaling does not increase capacity. What is the most likely reason?

Accepted Answer

The auto scaling configuration has a maximum capacity that prevents scaling beyond a certain limit.. Auto scaling uses the consumed capacity metric over a period. If the consumed capacity is consistently at 8,000 RCU, the target utilization is 70% of provisioned (10,000 RCU), so the current utilization is 80%, which is above the target. Auto scaling should increase capacity. However, auto scaling has a cooldown period and also scales based on sustained consumption. Option A is not correct because auto scaling can scale out. Option B is not correct because the table is not throttled yet. Option C is correct because auto scaling might be configured with a maximum capacity that limits scaling. Option D is not correct because auto scaling can increase RCU if needed.

Answer

The consumed capacity is still below the provisioned capacity, so no throttling occurs, and auto scaling does not trigger.

Answer

Auto scaling for DynamoDB does not support increasing read capacity; it only decreases capacity.

Answer

Auto scaling only scales out when the consumed capacity exceeds the provisioned capacity.

Question 12

A database administrator is troubleshooting a failover event for an Amazon RDS for SQL Server Multi-AZ DB instance. The failover occurred automatically. Which AWS service or feature should the administrator use to view the failover history and the reason for the failover?

Accepted Answer

The Amazon RDS console Events page.. Amazon RDS events are stored in the RDS console under 'Events' and also in CloudTrail. But the best place to see failover reasons is the RDS console events. Option B is correct because the RDS console shows events like 'failover' with reasons. Option A is wrong because CloudTrail records API calls, not internal failover reasons. Option C is wrong because CloudWatch Logs does not automatically log failover reasons. Option D is wrong because StatusInsis not a service.

Answer

Amazon CloudWatch Logs for the DB instance.

Answer

AWS CloudTrail logs to view the failover API call.

Answer

The AWS Status Dashboard.

Question 13

A company notices that its Amazon DynamoDB table is consuming more read capacity than expected. The table has a global secondary index (GSI) with a different sort key. Which action would most likely reduce the read consumption?

Accepted Answer

Enable DAX (DynamoDB Accelerator) to cache read results.. Queries that use the GSI can consume read capacity from the index. However, if the query uses the base table's primary key, it consumes from the base table. Option A is wrong because local secondary indexes don't help. Option B is wrong because adjusting write capacity doesn't affect reads. Option C is correct because enabling DynamoDB Accelerator (DAX) caches reads, reducing read capacity consumption. Option D is wrong because changing the sort key is not a direct solution.

Answer

Increase the write capacity of the table.

Answer

Change the sort key of the base table to match the GSI sort key.

Answer

Create a local secondary index (LSI) with the same sort key as the GSI.

Question 14

A company has an Amazon Aurora MySQL DB cluster with a primary instance and two Aurora Replicas. The application is experiencing high write latency. The primary instance's CPU utilization is at 90%, while the replicas are at 30%. The DB cluster parameter group has the default values. Which change is most likely to reduce write latency?

Accepted Answer

Disable the binary log (binlog) on the DB cluster.. High CPU on the primary could be due to the binary log (binlog) being enabled by default for Aurora MySQL. Option B is correct because disabling binlog reduces CPU overhead. Option A is wrong because increasing instance size would help but is not the most likely fix. Option C is wrong because read replicas don't affect write latency. Option D is wrong because increasing storage doesn't reduce CPU.

Answer

Increase the DB instance class of the primary instance.

Answer

Add more Aurora Replicas to distribute the write load.

Answer

Increase the allocated storage of the cluster.

Question 15

A developer is troubleshooting an application that uses Amazon DynamoDB. The application sometimes receives ProvisionedThroughputExceededException errors. The table has on-demand capacity mode. The errors occur in short bursts. What is the most likely cause?

Accepted Answer

The request rate exceeds the partition's throughput capacity in a short burst.. On-demand capacity mode can handle up to the table's previous peak traffic. However, if traffic spikes suddenly, DynamoDB might throttle. Option D is correct because on-demand has a limit on the maximum throughput per partition. Option A is wrong because indexes share the table's capacity. Option B is wrong because on-demand does not have provisioned limits. Option C is wrong because the table is on-demand, not provisioned.

Answer

The table has a low read/write capacity mode limit that needs to be increased.

Answer

The global secondary index (GSI) has a different throughput limit.

Answer

The table has reached the maximum provisioned throughput.