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

Question 1

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. Option D is correct because Aurora's Performance Insights with the 'Wait for lock' dimension can identify blocking sessions. Option A is wrong because Amazon Inspector is a security assessment tool. Option B is wrong because CloudWatch Logs Insights can analyze logs but does not directly identify blocking transactions. Option C is wrong because Enhanced Monitoring provides OS-level metrics, not database lock information.

Answer

Amazon Inspector

Answer

CloudWatch Logs Insights

Answer

Amazon RDS Enhanced Monitoring

Question 2

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. Option A is correct because CPUUtilization is a primary indicator of resource saturation. Option B is wrong because DatabaseConnections shows concurrent connections, not resource usage. Option C is wrong because FreeableMemory is important but CPU is more likely the first bottleneck. Option D is wrong because SwapUsage is relevant but not the first metric to check.

Answer

SwapUsage

Answer

FreeableMemory

Answer

DatabaseConnections

Question 3

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. Option B is correct because ReadThrottleEvents directly measures throttled read requests. Option A is wrong because ConsumedReadCapacityUnits shows actual usage, not throttled events. Option C is wrong because ThrottledRequests includes write throttles as well. Option D is wrong because ReadLatency shows latency, not throttling.

Answer

ReadLatency

Answer

ConsumedReadCapacityUnits

Answer

ThrottledRequests

Question 4

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.. Option C is correct because Amazon RDS Event Notifications for 'failover' events are delivered within seconds. Option A is wrong because CloudWatch metric 'DatabaseConnections' dropping to zero may indicate failover but the alarm evaluation period is typically 1 minute, causing delay. Option B is wrong because Enhanced Monitoring metrics have a granularity of 1 second but do not directly indicate failover. Option D is wrong because CloudTrail logs API calls like FailoverDBCluster but these are not real-time, often with minutes delay.

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 5

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.. Option A is correct because a low cache hit ratio indicates the cache is not being used effectively, often due to a low TTL. Option B is wrong because insufficient read replicas would not cause low cache hits. Option C is wrong because high CPU might cause latency but not necessarily low cache hits. Option D is wrong because insufficient write capacity is not relevant for ElastiCache read behavior.

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 6

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. Option D is correct because a failover results in a brief downtime (DatabaseConnections drop to zero) followed by a switch from master to standby (ReplicaLag disappears). Option A is wrong because WriteIOPS and ReadIOPS may change but not specifically indicate failover. Option B is wrong because FreeStorageSpace does not change during failover. Option C is wrong because NetworkThroughput may fluctuate but is not a direct indicator of failover.

Answer

FreeStorageSpace on the primary instance

Answer

WriteIOPS and ReadIOPS for both instances

Answer

NetworkThroughput on the replica instance

Question 7

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. Option B is correct because the 'service_class' column indicates the workload management (WLM) queue, which can show if the query is queued. Option A is wrong because 'query' is just the query ID. Option C is wrong because 'starttime' shows when the query started. Option D is wrong because 'aborted' indicates if the query was canceled, not waiting.

Answer

aborted

Answer

query

Answer

starttime

Question 8

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 D are correct. A high disk queue depth indicates I/O bottleneck. Increasing IOPS (Option B) or enabling Auto Scaling (Option D) can alleviate the bottleneck. Option A is wrong because more connections may increase I/O contention. Option C is wrong because query caching is not a primary solution for I/O. Option E is wrong because Multi-AZ does not improve I/O performance.

Answer

Increase the number of database connections.

Answer

Enable query caching in PostgreSQL.

Answer

Enable Multi-AZ deployment.

Question 9

A company uses Amazon DynamoDB with global tables. During a regional outage, the application fails over to the secondary region. After recovery, the DBA notices that the data in the secondary region is not fully consistent with the primary. Which THREE steps should the DBA take to diagnose the issue? (Choose THREE.)

Accepted Answer

Verify that DynamoDB Streams is enabled on the table.. Options A, C, and D are correct. Checking ReplicationLatency (A) identifies replication lag. Reviewing CloudWatch Logs for error logs (C) can reveal replication errors. Checking DynamoDB Streams (D) ensures changes are being captured. Option B is wrong because disabling global tables is not a diagnostic step. Option E is wrong because increasing write capacity does not fix consistency issues.

Answer

Disable and re-enable global tables to force resync.

Answer

Increase the write capacity on the secondary table.

Question 10

A company is running a critical Oracle database on Amazon RDS. The DBA wants to set up monitoring to detect if the database is experiencing a high number of full table scans, which may indicate missing indexes. Which TWO metrics should the DBA monitor? (Choose TWO.)

Accepted Answer

TableScanRows. Options B and D are correct. FullTableScans (B) directly counts full scan operations. TableScanRows (D) indicates the number of rows read via full scans. Option A is wrong because BufferCacheHitRatio indicates cache efficiency, not full scans. Option C is wrong because UserCommits shows transaction commits. Option E is wrong because RedoLogSpaceUsage relates to write-ahead logging.

Answer

BufferCacheHitRatio

Answer

UserCommits

Answer

RedoLogSpaceUsage

Question 11

A company is running an Amazon RDS for PostgreSQL DB instance with Multi-AZ deployment. They notice that the primary DB instance is experiencing high CPU utilization. The read replica shows normal CPU. Which action should the DBA take to reduce the load on the primary instance?

Accepted Answer

Offload SELECT queries to the read replica. Option A is correct because moving read-intensive workloads to the read replica reduces CPU on the primary. Option B is wrong because Multi-AZ failover does not help with CPU load. Option C is wrong because increasing instance size would help but is not the best first step. Option D is wrong because read replicas are asynchronous and cannot be used for writes.

Answer

Failover to the standby instance

Answer

Increase the DB instance size

Answer

Convert the read replica to a Multi-AZ standby

Question 12

A database team uses Amazon DynamoDB with auto scaling enabled. They observe frequent throttling on a table during peak hours. The table's read capacity is set to 5000 RCU with auto scaling range 3000-7000. The consumed read capacity graph shows spikes to 6000 RCU but throttling occurs at 5500. What is the most likely cause?

Accepted Answer

Auto scaling cannot react quickly enough to sudden traffic spikes. Option D is correct because auto scaling uses a target utilization (default 70%) and cannot scale fast enough for sudden spikes. Option A is wrong because auto scaling is enabled. Option B is wrong because WCU are separate. Option C is wrong because partition count doesn't directly cause throttling if RCU is sufficient.

Answer

Write capacity units are insufficient

Answer

Auto scaling is disabled for the table

Answer

The table has too many partitions

Question 13

A developer is troubleshooting a slow query on Amazon RDS for MySQL. The query joins three large tables and runs frequently. What is the most effective way to identify the bottleneck?

Accepted Answer

Enable the slow query log and analyze the output. Option B is correct because enabling slow query log captures queries that exceed a threshold, allowing analysis. Option A is wrong because Enhanced Monitoring shows OS metrics, not query details. Option C is wrong because Performance Insights shows wait events and SQL, but slow query log specifically targets slow queries. Option D is wrong because CloudWatch metrics show overall performance, not per-query.

Answer

Check the RDS Events for any maintenance notifications

Answer

Review Amazon CloudWatch CPU and memory metrics

Answer

Use AWS Database Migration Service to migrate to a larger instance

Question 14

A company uses Amazon ElastiCache for Redis as a caching layer for a web application. They notice increased latency and cache miss rates. The cache cluster has 5 nodes with replication. Which metric should be monitored to identify if the cache is under-provisioned?

Accepted Answer

CPUUtilization. Option A is correct because high CPUUtilization indicates the cache nodes are overloaded. Option B is wrong because CacheHits are a measure of effectiveness, not provisioning. Option C is wrong because Evictions occur when memory is full but CPU is more direct for throughput. Option D is wrong because ReplicationLag indicates replication issues, not capacity.

Answer

ReplicationLag

Answer

CacheHits

Answer

Evictions

Question 15

A company runs an Amazon Aurora MySQL DB cluster with one writer and two readers. They notice that one reader instance is consistently showing higher than expected lag. The other reader is fine. What is the most likely cause?

Accepted Answer

The reader instance is being used for heavy analytical queries. Option C is correct because an imbalanced workload on that reader can cause it to lag. Option A is wrong because writer load affects all replicas. Option B is wrong because network issues would affect both readers. Option D is wrong because parameter group change would affect both readers if applied to cluster.

Answer

The writer instance is experiencing high write activity

Answer

There is a network connectivity issue between the writer and that reader

Answer

The reader instance has a different DB parameter group