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

Question 1

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?

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

Accepted Answer

Disable the binary log (binlog) on the DB cluster.. High CPU utilization on the primary instance is often caused by the binary log (binlog) being enabled, which is enabled by default for Aurora MySQL. Binlog generation adds overhead to write operations. Disabling binlog reduces CPU usage on the primary, thereby reducing write latency. Increasing the instance class (Option A) could help but is not as directly targeted as disabling binlog. Adding more Aurora Replicas (Option B) does not reduce write latency on the primary because replicas handle read traffic only. Increasing allocated storage (Option D) does not affect CPU or write latency.

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 2

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.

Question 3

A company runs an Amazon RDS for Oracle DB instance. The database administrator wants to receive an alert when the storage space is below 10% of the allocated storage. Which Amazon CloudWatch metric and alarm threshold should be used?

Accepted Answer

Metric: FreeStorageSpace, Condition: < 10% of 100 GB (10 GB). The correct metric is FreeStorageSpace, which reports the available storage in bytes. To alert when storage is below 10% of allocated, compute the threshold as 10% of the total allocated storage (e.g., 10 GB for 100 GB). Option A defines the condition correctly. Option B is wrong because BinaryLogUsage applies to MySQL, not Oracle. Option C is incorrect as FreeableMemory tracks memory, not storage. Option D is wrong because DiskQueueDepth measures I/O queue depth, not storage capacity.

Answer

Metric: BinaryLogUsage, Condition: > 10%

Answer

Metric: FreeableMemory, Condition: < 10% of total memory

Answer

Metric: DiskQueueDepth, Condition: > 10

Question 4

A company uses Amazon DynamoDB with a table that has a partition key of 'user_id' (string) and sort key of 'timestamp' (number). The application queries for recent items for a specific user using the query API with KeyConditionExpression. The query returns items in descending order. Occasionally, the query returns items that are not the most recent. What is the most likely cause?

Accepted Answer

The query is using eventually consistent reads, which may not reflect the latest writes.. DynamoDB queries by default use eventually consistent reads, which may not reflect the latest writes. In this scenario, the query is likely using eventually consistent reads, causing it to return stale data. Option A is correct. Option B is incorrect because ScanIndexForward set to false returns items in descending order, which is what the application expects. Option C is incorrect because pagination would result in missing items, not stale data. Option D is incorrect because the query is on the base table, not a GSI.

Answer

The query is not using the ScanIndexForward parameter set to false.

Answer

The query results are paginated and the application is not iterating through all pages.

Answer

The query is using a global secondary index (GSI) that has a different sort key.

Question 5

A company is troubleshooting an Amazon RDS for MySQL DB instance that is experiencing high CPU utilization. The DB instance is a db.t3.medium. Which TWO actions should the database administrator take to investigate the cause?

Accepted Answer

Enable Performance Insights to identify the top SQL queries consuming CPU.. Enabling Performance Insights provides visibility into which SQL queries are consuming CPU resources. Option E is correct because reviewing the slow query log helps identify queries with long execution times that may be causing high CPU. Option B is incorrect because disabling Multi-AZ does not help investigate CPU utilization; it reduces availability but not CPU. Option C is incorrect because increasing the query cache size is a tuning action, not an investigative step, and may not address the root cause. Option D is incorrect because increasing the DB instance class is a scaling fix, not an investigation method.

Answer

Disable Multi-AZ to reduce overhead.

Answer

Modify the DB parameter group to increase the query cache size.

Answer

Increase the DB instance class to a larger size.

Question 6

A company is using Amazon DynamoDB with auto scaling enabled. The table has a provisioned read capacity of 10,000 RCU and write capacity of 5,000 WCU. Auto scaling target utilization is 70%. The table experiences a sudden spike in read traffic, reaching 12,000 RCU. The table throttles some requests. Which THREE actions should the company take to prevent future throttling?

Accepted Answer

Implement exponential backoff in the application to retry throttled requests.. Implementing exponential backoff with jitter helps handle throttled requests gracefully by retrying after increasing delays, reducing further load on the table. Option B is correct because increasing the maximum read capacity in the auto scaling configuration allows the table to scale up further (beyond 10,000 RCU) during traffic spikes, preventing throttling. Option E is correct because enabling DynamoDB Accelerator (DAX) caches read requests, offloading the table and reducing the read load that can cause throttling. Option C is wrong because decreasing the target utilization would cause auto scaling to trigger earlier, but it does not increase the maximum capacity; the table would still be limited to the max capacity set, and the spike might exceed it. Option D is wrong because the issue is read traffic, not write capacity, so increasing write capacity does not address read throttling.

Answer

Decrease the auto scaling target utilization to 50% to scale out earlier.

Answer

Increase the write capacity to 10,000 WCU.

Question 7

A database administrator is monitoring an Amazon RDS for PostgreSQL DB instance. The administrator notices that the DB instance is using more memory than expected. Which TWO metrics in Amazon CloudWatch can help diagnose memory usage?

Accepted Answer

FreeableMemory. The correct answers are FreeableMemory (B) and SwapUsage (E). FreeableMemory reflects the amount of available memory on the instance; a low value indicates high memory usage. SwapUsage tracks the amount of swap space being used; when memory is exhausted, the OS begins swapping, which directly indicates memory pressure. The other metrics are unrelated to memory: NetworkReceiveThroughput (A) measures network traffic, ReadIOPS (C) measures I/O operations, and DatabaseConnections (D) shows the number of connections, not memory consumption.

Answer

NetworkReceiveThroughput

Answer

ReadIOPS

Answer

DatabaseConnections

Question 8

A company is using Amazon RDS for MySQL with Multi-AZ deployment. The application team reports increased latency during peak hours. Which AWS service should the database specialist use to identify the root cause?

Accepted Answer

Enable Performance Insights for the RDS instance and analyze the database load.. Performance Insights provides detailed database performance metrics and helps identify bottlenecks such as high load or slow queries. Option B is wrong because AWS Config tracks configuration changes, not performance. Option C is wrong because CloudWatch Metrics Dashboard shows aggregated metrics but lacks the granular database analysis needed for root cause identification. Option D is wrong because Amazon Inspector is a security assessment tool, not a performance monitoring service.

Answer

Enable AWS Config to track configuration changes to the RDS instance.

Answer

Use the CloudWatch Metrics Dashboard to analyze database connections.

Answer

Run an Amazon Inspector assessment on the RDS instance.

Question 9

A database specialist is troubleshooting an Amazon RDS for PostgreSQL instance that is experiencing intermittent connection timeouts. The application logs show errors like 'FATAL: remaining connection slots are reserved for non-replication superuser connections'. The max_connections parameter is set to 100. What should the specialist do to resolve this issue?

Accepted Answer

Modify the 'max_connections' parameter to a higher value and reboot the instance.. The error indicates that the maximum number of connections has been reached. Increasing the max_connections parameter allows more concurrent connections, resolving the issue. Option B is incorrect because the error is about regular connections, not replication slots. Option C is incorrect because the superuser_reserved_connections parameter reserves slots for superusers; the error is about all connection slots being exhausted. Option D is incorrect because RDS Proxy manages connection pooling but does not increase the connection limit.

Answer

Increase the 'max_replication_slots' parameter to allow more replication connections.

Answer

Increase the value of the 'superuser_reserved_connections' parameter.

Answer

Enable RDS Proxy to manage database connections efficiently.

Question 10

A company is running a production Amazon DynamoDB table and notices that read requests are being throttled. The table has on-demand capacity mode enabled. Which action should the database specialist take to troubleshoot the throttling?

Accepted Answer

Check the CloudWatch metric 'ThrottledRequests' for the table and review 'SystemErrors' to identify hot partitions.. With on-demand capacity, throttling often results from hot partitions. The CloudWatch metric 'ThrottledRequests' helps detect throttling, and reviewing 'SystemErrors' can indicate partition-level errors, aiding in identifying hot partitions. Option B is incorrect because auto scaling is only supported for provisioned capacity mode, not on-demand. Option C is incorrect because enabling DAX can reduce read load but does not address the root cause of throttling due to hot partitions; it is not a troubleshooting step. Option D is incorrect because switching to provisioned capacity and increasing RCUs is a remediation action, not a troubleshooting action.

Answer

Enable auto scaling on the table to automatically adjust capacity.

Answer

Enable DynamoDB Accelerator (DAX) to reduce read load on the table.

Answer

Switch the table to provisioned capacity mode and increase the read capacity units.

Question 11

A database specialist is troubleshooting an Amazon RDS for SQL Server instance that is running out of storage. The instance has 500 GB of provisioned storage and is using General Purpose SSD (gp2). The specialist wants to set up an alarm to notify when free storage space drops below 50 GB. Which CloudWatch metric and threshold should be used?

Accepted Answer

Monitor the 'FreeStorageSpace' metric in bytes and set a threshold of 53687091200.. The correct metric is 'FreeStorageSpace' which is reported in bytes by CloudWatch for Amazon RDS. 50 GB equals 50 × 1024³ = 53,687,091,200 bytes. Therefore, setting a threshold of 53687091200 bytes triggers the alarm when free space drops below 50 GB. Option A is incorrect because 'FreeStorageSpace' is not available in percent; you must use bytes. Option B is incorrect because 'DiskSpaceUtilization' is not a standard CloudWatch metric for RDS (it is used for EC2). Option D is incorrect because although 'FreeStorageSpace' is the right metric, the threshold must be specified in bytes, not gigabytes; CloudWatch does not accept a unit other than bytes for this metric.

Answer

Monitor the 'FreeStorageSpace' metric in percent and set a threshold of 10.

Answer

Monitor the 'DiskSpaceUtilization' metric and set a threshold of 90.

Answer

Monitor the 'FreeStorageSpace' metric in gigabytes and set a threshold of 50.

Question 12

A company is using Amazon ElastiCache for Redis to cache frequently accessed data. Recently, the application has been experiencing increased latency. The database specialist suspects that the cache hit ratio has decreased. Which CloudWatch metric should the specialist analyze to confirm this suspicion?

Accepted Answer

Monitor 'CacheHits' and 'CacheMisses' metrics to calculate the hit ratio.. The cache hit ratio is calculated as CacheHits / (CacheHits + CacheMisses). Monitoring the 'CacheHits' and 'CacheMisses' CloudWatch metrics allows the specialist to compute the hit ratio and confirm whether it has decreased, which would explain increased latency. Option A is incorrect because CurrConnections shows the number of connections, not the cache hit ratio. Option B is incorrect because Evictions indicates keys being evicted, which can affect the cache but does not directly measure the hit ratio. Option D is incorrect because ReplicationLag measures replication delay, not cache performance.

Answer

Monitor the 'CurrConnections' metric to see if there are too many connections.

Answer

Monitor the 'Evictions' metric to see if keys are being evicted.

Answer

Monitor the 'ReplicationLag' metric to check replication delay.

Question 13

A database specialist is trying to connect to an Amazon RDS for MySQL instance from an EC2 instance but receives a 'Connection timed out' error. The security group for the RDS instance allows inbound traffic on port 3306 from the security group of the EC2 instance. What should the specialist check next?

Accepted Answer

Check the network ACL associated with the subnet of the RDS instance to ensure it allows inbound traffic on port 3306 and outbound traffic on ephemeral ports.. The 'Connection timed out' error suggests the packet is being dropped at the network layer, likely by a network ACL. Since the security group allows inbound on port 3306, the next step is to check the network ACL associated with the RDS instance's subnet. Network ACLs are stateless, so they must allow both inbound traffic on port 3306 and outbound traffic on ephemeral ports for the response. Option B is incorrect because a timed out error occurs before the TCP handshake completes, so DNS resolution is not the issue. Option C is incorrect because an internet gateway and public route are irrelevant if both instances are in the same VPC or connected privately. Option D is incorrect because the security group for the EC2 instance can be stateful and typically allows outbound traffic by default; the timeout is not caused by missing outbound rules on the EC2 side.

Answer

Check that the RDS instance has a public DNS name and the EC2 instance can resolve it.

Answer

Ensure that the VPC has an internet gateway attached and the route table has a route to it.

Answer

Verify that the security group for the EC2 instance allows outbound traffic on port 3306.

Question 14

A company is running an Amazon Aurora MySQL database cluster. The database specialist notices that the write latency is high during peak hours. The cluster consists of one writer and two reader instances. Which action should the specialist take to reduce write latency?

Accepted Answer

Increase the instance class of the writer instance to a larger size.. Increasing the instance class of the writer instance provides more CPU and memory resources, which can directly improve write throughput and reduce write latency during peak loads. Option A is incorrect because Auto Scaling in Aurora adjusts the number of reader instances, not the writer capacity. Option C is incorrect because Multi-AZ is already inherent in Aurora; enabling Multi-AZ does not affect write latency. Option D is incorrect because adding more reader instances distributes read traffic but does not reduce write latency on the writer.

Answer

Enable Auto Scaling on the cluster to automatically adjust capacity.

Answer

Enable Multi-AZ deployment for the cluster.

Answer

Add more reader instances to distribute the read load.

Question 15

A company is using Amazon DynamoDB with global tables. The application team reports that data written in one region is not immediately available in another region. The database specialist needs to monitor the replication lag. Which CloudWatch metric should be used?

Accepted Answer

Monitor the 'ReplicationLatency' metric in the replica region.. 'ReplicationLatency' is the CloudWatch metric that measures the time between an update to a DynamoDB global table in the source region and its appearance in the replica region. Option A is wrong because 'ConsumedWriteCapacityUnits' measures the amount of write capacity consumed, not replication lag. Option B is wrong because 'PendingReplicationCount' shows the number of items waiting to be replicated, not the time delay. Option C is wrong because 'ThrottledRequests' indicates that requests are being throttled, which is unrelated to replication lag.

Answer

Monitor the 'ConsumedWriteCapacityUnits' metric in both regions.

Answer

Monitor the 'PendingReplicationCount' metric in the source region.

Answer

Monitor the 'ThrottledRequests' metric in the source region.