DBS-C01 Monitoring and Troubleshooting Practice Test 21 — 15 Questions

Question 1

A developer notices that an Amazon ElastiCache for Redis cluster is experiencing high latency. The cluster uses a single node. Which CloudWatch metric should be reviewed first to determine if the issue is due to memory pressure?

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

Accepted Answer

DatabaseMemoryUsagePercentage. DatabaseMemoryUsagePercentage is the CloudWatch metric that reports the percentage of memory used by the Redis engine on the node. High values (approaching 100%) indicate memory pressure, which can trigger evictions, swap usage, or write failures, all of which cause latency. This is the first metric to review when diagnosing memory-related latency on a single-node ElastiCache for Redis cluster.

Answer

NetworkBytesIn

Answer

ReplicationLag

Answer

CPUUtilization

Question 2

A database administrator notices that an Amazon RDS for Oracle instance has a high number of connections, causing performance degradation. Which tool can be used to identify the active sessions and their queries?

Accepted Answer

Performance Insights. Performance Insights provides a dashboard to monitor active sessions and the queries they are running. Option A is incorrect because Amazon Inspector is a security assessment tool, not a monitoring tool for database sessions. Option C is incorrect because RDS Enhanced Monitoring provides OS-level metrics like CPU and memory, not database session details. Option D is incorrect because AWS CloudTrail logs API calls, not database sessions or queries.

Answer

Amazon Inspector

Answer

RDS Enhanced Monitoring

Answer

AWS CloudTrail

Question 3

A developer needs to monitor the number of throttled read requests for a DynamoDB table. Which CloudWatch metric should be used?

Accepted Answer

ReadThrottleEvents. The CloudWatch metric ReadThrottleEvents specifically counts the number of read requests that were throttled because they exceeded the provisioned read capacity or the maximum throughput for the table or index. It is the direct metric to monitor for throttled read requests. By tracking this metric, developers can identify when read capacity is insufficient and take action, such as increasing provisioned capacity or switching to on-demand mode.

Answer

ThrottledWriteEvents

Answer

SuccessfulRequestLatency

Answer

ConsumedReadCapacityUnits

Question 4

Which TWO CloudWatch metrics should be monitored to detect storage performance issues for an Amazon RDS for MySQL instance? (Choose two.)

Accepted Answer

WriteIOPS. WriteIOPS (C) and ReadIOPS (E) are the correct CloudWatch metrics for detecting storage performance issues on an Amazon RDS for MySQL instance, because they directly measure the number of read and write operations per second hitting the underlying EBS storage, and degraded storage performance typically manifests as elevated I/O latency or throughput saturation visible through these I/O metrics. DatabaseConnections (B) only reflects the count of active client connections and indicates connection pressure rather than storage performance. CPUUtilization (D) measures compute load on the DB instance and, while it can be affected by I/O waits, it does not directly isolate storage performance. NetworkReceiveThroughput (A) tracks inbound network traffic to the instance, which is unrelated to disk-level read/write performance.

Answer

NetworkReceiveThroughput

Answer

DatabaseConnections

Answer

CPUUtilization

Question 5

A database administrator notices that an Amazon RDS for Oracle DB instance's CPU utilization is consistently above 90% during peak hours. The application is read-heavy. Which action can reduce CPU load?

Accepted Answer

Create a read replica and direct read traffic to it. For a read-heavy workload on RDS for Oracle, offloading read traffic to a read replica is the most direct way to reduce CPU load on the primary instance. Read replicas receive asynchronous replication from the primary and serve read-only queries, freeing the primary's CPU for writes and other operations. This is a standard horizontal scaling pattern for read-heavy RDS workloads.

Answer

Disable Multi-AZ to free up resources

Answer

Increase the allocated storage

Answer

Enable Performance Insights to optimize queries

Question 6

A company uses Amazon Redshift for data warehousing. They run a daily ETL job that loads data into the cluster. Recently, the job started failing with 'Disk Full' errors. The cluster has 5 RA3 nodes. Which step should be taken to resolve the issue?

Accepted Answer

Resize the cluster to a larger node type or add more nodes. Resize the cluster to a larger node type or add more nodes. RA3 nodes use managed storage with a local cache, and a 'Disk Full' error typically indicates that the local cache or the overall storage limit for the cluster is exhausted. Resizing adds more local cache and increases the total managed storage capacity, resolving the disk full error. Option A is incorrect because disabling concurrency scaling does not free up disk space; it only affects query concurrency. Option B is incorrect because VACUUM reclaims space from deleted rows, but it requires temporary disk space; if the disk is already full, VACUUM may fail or not help. Option D is incorrect because Redshift Spectrum allows querying data directly from S3 without loading it into Redshift, but it does not resolve a disk full error on the Redshift cluster itself.

Answer

Disable concurrency scaling to free up resources

Answer

Run a VACUUM command to reclaim space from deleted rows

Answer

Enable Redshift Spectrum to offload queries to S3

Question 7

An application uses Amazon ElastiCache for Redis as a session store. Users report that sessions are being lost intermittently. The ElastiCache cluster has replication enabled with one replica. CloudWatch metrics show 'Evictions' spiking during peak hours. What is the MOST likely cause?

Accepted Answer

The cache's memory is full and the eviction policy is removing keys. A spike in 'Evictions' CloudWatch metric indicates that the cache's memory is full, and ElastiCache is evicting keys based on the configured eviction policy (e.g., allkeys-lru). This removal of keys directly causes session data to be lost. Option A is incorrect: replication lag can cause stale reads but not evictions or loss of keys. Option B is incorrect: encryption in transit does not affect memory usage or evictions. Option D is incorrect: automatic snapshots may cause a brief latency spike but do not result in evictions.

Answer

Replication lag between primary and replica is causing read failures

Answer

Encryption in transit is enabled and causes decryption errors

Answer

The cluster is performing automatic snapshots that block writes

Question 8

A company uses Amazon DynamoDB and notices that some queries are taking longer than expected. The table has a partition key only. The 'ConsumedReadCapacityUnits' is below the provisioned throughput. What is the most likely cause of the slow queries?

Accepted Answer

The partition key is not distributed evenly, causing hot partitions. If the partition key is not chosen well, data can be skewed, causing hot partitions. Even if total consumed capacity is below provisioned, a single partition may receive more requests than its share of capacity, causing throttling on that partition, which slows queries. Option A is wrong because DAX is a caching layer that speeds up reads, not slows them. Option B is wrong because global tables replication does not affect read latency on the source table. Option C is wrong because DynamoDB Streams do not consume read capacity for reads from the table; they use separate capacity.

Answer

DAX is misconfigured and slowing down reads

Answer

Global tables replication is causing delays

Answer

DynamoDB Streams is enabled and consuming read capacity

Question 9

A database administrator is troubleshooting an Amazon RDS for SQL Server instance that is experiencing high 'ReadIOPS' and 'ReadLatency'. The instance uses General Purpose SSD (gp2) storage. The 'BurstBalance' metric is 0%. What should the administrator do to improve performance?

Accepted Answer

Increase the allocated storage or switch to Provisioned IOPS. The BurstBalance metric at 0% indicates that the gp2 volume has exhausted its burst credits, causing high ReadIOPS and ReadLatency. To improve performance, the administrator should either increase the allocated storage (which increases baseline IOPS for gp2) or switch to Provisioned IOPS (io1/io2) storage, which provides dedicated IOPS regardless of burst credits. This directly addresses the root cause of the performance degradation.

Answer

Enable Multi-AZ to distribute the load

Answer

Create a read replica to offload read traffic

Answer

Disable automatic backups to reduce I/O

Question 10

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. ReadIOPS (A) is correct because it reports the average number of disk read I/O operations per second, so a sustained high or spiking ReadIOPS value directly signals heavy read activity that can saturate the underlying EBS storage and reveal an I/O bottleneck. DiskQueueDepth (C) is correct because it measures the number of outstanding I/O requests waiting to be serviced; a growing queue indicates the storage subsystem cannot keep up with demand, which is a classic indicator of an I/O bottleneck. FreeStorageSpace (B) is not marked correct because it only shows remaining allocated storage and relates to capacity exhaustion, not I/O throughput or latency. DatabaseConnections (D) is not marked correct because it reflects the number of active client sessions, which points to connection or concurrency issues rather than disk I/O pressure. CPUUtilization (E) is not marked correct because it measures compute load on the DB instance, which can be high for reasons unrelated to storage I/O and does not directly identify an I/O bottleneck.

Answer

FreeStorageSpace

Answer

DatabaseConnections

Answer

CPUUtilization

Question 11

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 B is wrong because ReadIOPS measures I/O operations, not memory. Option C is wrong because DatabaseConnections tracks connections, not memory. Option D is wrong because CPUUtilization measures CPU, 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 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.. The Amazon RDS console Events page stores RDS events, including failover events with reasons. This is the best place to view failover history and reason. CloudTrail records API calls but not internal failover reasons. CloudWatch Logs does not automatically log failover reasons. The AWS Status Dashboard shows service health, not instance-specific failover history.

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 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.. In on-demand capacity mode, DynamoDB automatically scales to handle traffic, but it still has per-partition throughput limits. If a short burst of requests exceeds the partition's capacity, ProvisionedThroughputExceededException can occur even in on-demand mode. This is because on-demand tables are subject to the same partition-level limits as provisioned tables, and sudden spikes may not be instantly absorbed. The other options are incorrect because on-demand mode does not have provisioned throughput limits (A, C) and GSIs have their own throughput but the error is on the table (B).

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 14

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 15

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.. Option A is correct because Performance Insights provides a database load view that breaks down CPU consumption by SQL statement, wait event, and user, letting the DBA pinpoint the exact top SQL queries driving high CPU on the db.t3.medium instance. Option E is correct because the MySQL slow query log records statements whose execution time exceeds long_query_time, so reviewing it (after setting slow_query_log=1 and an appropriate long_query_time) reveals long-running queries that are likely culprits. Option B is not appropriate because Multi-AZ is a high-availability feature and disabling it does not reduce CPU load on the primary; it only removes the standby. Option C is wrong because the MySQL query cache is deprecated in MySQL 5.7 and removed in 8.0, and increasing it would not diagnose the cause. Option D is wrong because resizing the instance class is a remediation action, not an investigation step, and it does not identify the root cause.

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.