DBS-C01 Practice Exam 64 — 20 Questions

Question 1

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 2

A company uses Amazon DynamoDB global tables for a multi-region application. They notice that writes in one region are not appearing in another region after several minutes. What should they check first?

Accepted Answer

Check the ReplicationLatency metric in Amazon CloudWatch. Option C is correct because ReplicationLatency metric shows delay between regions. Option A is wrong because Streams are used for replication; check the metric first. Option B is wrong because auto scaling affects capacity, not replication. Option D is wrong because table size doesn't directly cause replication delay.

Answer

Verify that auto scaling is configured identically in both regions

Answer

Ensure DynamoDB Streams are enabled on the table

Answer

Check the table size in both regions

Question 3

A company is using Amazon DynamoDB with provisioned capacity. They notice an increase in throttled write requests. The workload consists of writes to a single partition key. Which TWO actions would help reduce throttling?

Accepted Answer

Increase the provisioned write capacity units.. Options A and C are correct. Using DynamoDB Accelerator (DAX) reduces read load but does not help with writes; option B is irrelevant. Option D is for read scaling. Option E (using write sharding) distributes writes across partitions. Option C (increasing write capacity) directly addresses throttling. Option A (adaptive capacity) helps but may not fully resolve hot partition; however, it is a valid action. The question expects A and C as the most direct.

Answer

Add a global secondary index with a different partition key.

Answer

Use DynamoDB Accelerator (DAX) for write caching.

Answer

Implement write sharding by adding a suffix to the partition key.

Question 4

A company notices that its Aurora MySQL cluster has a high number of locks and deadlocks. The application uses read replicas for read scaling. What is the MOST likely cause?

Accepted Answer

Long-running transactions on the writer instance. Option B is correct because long-running transactions on the writer hold locks, increasing deadlocks. Option A is wrong because read replicas do not cause locks on writer. Option C is wrong because different instance sizes do not cause deadlocks. Option D is wrong because Performance Insights is diagnostic, not a cause.

Answer

Performance Insights is enabled

Answer

The writer and reader instances are of different sizes

Answer

Read replicas are performing write operations

Question 5

Which THREE actions should be taken to troubleshoot an Amazon RDS for PostgreSQL instance that is unresponsive? (Choose 3.)

Accepted Answer

Verify that the security group allows inbound traffic on the database port. Options A, C, and D are correct because checking logs, verifying security groups, and reviewing metrics are standard initial steps. Option B is wrong because rebooting without diagnostics may lose evidence. Option E is wrong because modifying instance class without cause may not help and could be disruptive.

Answer

Reboot the DB instance immediately

Answer

Modify the DB instance to a larger instance class

Question 6

An Amazon RDS for Oracle instance is experiencing high swap usage. Which metric should be monitored to determine if the instance is memory-constrained?

Accepted Answer

SwapUsage. SwapUsage indicates that the instance is using swap space, which is a sign of memory pressure. CPUUtilization is for CPU, not memory. FreeableMemory shows available memory, but swap usage directly indicates memory constraint.

Answer

CPUUtilization

Answer

WriteIOPS

Answer

FreeableMemory

Question 7

A company is using Amazon DynamoDB with a global table in two regions. The application is experiencing high write latency on the replica table in the secondary region. Which THREE factors could contribute to this issue?

Accepted Answer

Large item sizes being written to the table.. Global tables replicate writes asynchronously; network latency between regions affects replication. The write capacity on the replica table must be sufficient to handle replication writes. Item size affects write latency. Option D (read capacity) does not affect write latency. Option E (auto scaling) is not a direct cause of high latency.

Answer

Auto scaling configuration on the replica table.

Answer

Low read capacity on the replica table.

Question 8

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 9

Which THREE actions should be taken to troubleshoot a high number of ThrottlingExceptions from Amazon DynamoDB? (Choose 3.)

Accepted Answer

Examine the ConsumedWriteCapacity and ThrottledWriteCount metrics in CloudWatch. A, C, D are correct. Examining CloudWatch metrics helps identify throttling patterns. Implementing exponential backoff is a best practice. Increasing provisioned capacity resolves throttling. B is wrong because enabling DynamoDB Streams does not affect throttling. E is wrong because changing consistency model does not affect write throttling.

Answer

Enable DynamoDB Streams to offload writes

Answer

Change the read consistency to eventual

Question 10

A company is running a MongoDB-compatible Amazon DocumentDB cluster with one writer and two readers. The application writes a large amount of data during batch processing, and after a batch completes, the writer's CPU is high, and the readers have significant replica lag. The team wants to reduce replica lag without affecting the batch performance. What should they do?

Accepted Answer

Increase the instance size of the readers to improve apply throughput. Option D is correct because the replica lag is due to the readers applying writes from the oplog; increasing the reader instance size gives them more CPU and memory to apply writes faster. Option A is incorrect because increasing the writer size does not directly help readers. Option B is incorrect because decreasing the batch size reduces writes but the team wants to maintain performance. Option C is incorrect because changing the storage type does not affect replica lag.

Answer

Change the storage type to Provisioned IOPS on all instances

Answer

Reduce the batch size to lower the write rate

Answer

Increase the instance size of the writer to handle the batch faster

Question 11

A company uses Amazon ElastiCache for Redis. They want to monitor cache hit ratio. Which TWO metrics should be used to calculate the cache hit ratio?

Accepted Answer

CacheHits. Options A and C are correct. Cache hit ratio = CacheHits / (CacheHits + CacheMisses). CurItems is for memory usage, Evictions is for memory pressure, and GetTypeCmds is total get commands.

Answer

GetTypeCmds

Answer

Evictions

Answer

CurItems

Question 12

An administrator notices that the CloudWatch metric 'ReadLatency' for an Amazon RDS for SQL Server instance has increased significantly. Which of the following is the most likely cause?

Accepted Answer

The DB instance does not have enough provisioned IOPS.. High ReadLatency indicates that read operations are taking longer. This can be due to high I/O wait, which can be caused by insufficient I/O throughput (provisioned IOPS). Option A is correct: insufficient IOPS can cause latency. Option B is incorrect: high CPU may cause slower processing but not directly read latency. Option C is incorrect: network bandwidth does not directly affect storage latency. Option D is incorrect: memory pressure can cause swapping, which affects latency but not as directly as IOPS.

Answer

The DB instance is experiencing high CPU utilization.

Answer

The DB instance is running out of memory.

Answer

The DB instance is using a burstable instance class that has exhausted its credits.

Question 13

A database administrator notices that an Amazon RDS for MySQL DB instance's CPU utilization is consistently above 90% during peak hours. Which initial troubleshooting step should the administrator take?

Accepted Answer

Use Amazon RDS Performance Insights to identify the queries consuming CPU.. Option C is correct because Performance Insights provides detailed database performance metrics and helps identify the root cause of high CPU usage. Option A is wrong because increasing instance size is a reactive measure, not a troubleshooting step. Option B is wrong because enabling Multi-AZ addresses high availability, not performance. Option D is wrong because deleting slow query logs would remove diagnostic data.

Answer

Increase the DB instance size to handle the load.

Answer

Enable Multi-AZ deployment to distribute the load.

Answer

Disable slow query logging to reduce CPU overhead.

Question 14

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 15

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 16

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

Question 17

A financial services company runs a critical application on Amazon DynamoDB. Recently, they observed increased latency and throttled requests. Upon reviewing CloudWatch metrics, they see that WriteCapacityUnits consumed is consistently below the provisioned capacity, but ReadCapacityUnits consumed is frequently at 100%. The application performs equal mix of strongly consistent reads and writes. What is the most likely cause of the throttling?

Accepted Answer

Hot partitions causing uneven read traffic distribution.. Option A is correct because throttling on reads with provisioned capacity still available indicates hot partitions. Option B is wrong because writes are not throttled. Option C is wrong because adaptive capacity helps but does not eliminate hot partitions. Option D is wrong because strongly consistent reads consume twice the read capacity units, but the issue is hot partitions.

Answer

Adaptive capacity is automatically adjusting partition throughput.

Answer

Write capacity is insufficient for the workload.

Answer

Strongly consistent reads are consuming twice the RCU.

Question 18

A company is using Amazon DynamoDB with auto scaling enabled. The application is experiencing higher than expected write throttling. Which action should be taken to resolve this issue?

Accepted Answer

Increase the minimum provisioned capacity for the table.. Auto scaling can lag behind sudden traffic spikes. Increasing the minimum provisioned capacity can help reduce throttling during bursts. Option B is correct. Option A is incorrect because on-demand mode may be costly but could solve throttling, but the question asks for a resolution with auto scaling. Option C is incorrect because auto scaling already adjusts capacity. Option D is incorrect because decreasing capacity would worsen throttling.

Answer

Disable auto scaling and set a fixed provisioned capacity.

Answer

Decrease the maximum provisioned capacity to limit writes.

Answer

Switch the table to on-demand capacity mode.

Question 19

A company uses Amazon DynamoDB with on-demand capacity. Users report increased latency during peak hours. The application uses the DynamoDB API. Which monitoring metric should be examined first to identify throttling issues?

Accepted Answer

ThrottledRequests. Option B is correct because ThrottledRequests indicates requests that were rejected due to exceeding capacity. Option A is wrong because ConsumedWriteCapacityUnits might be lower than expected if throttling occurs, but it does not directly show throttled requests. Option C is wrong because SuccessfulRequestLatency is a latency metric, not a throttling indicator. Option D is wrong because ReadThrottleEvents is a CloudWatch metric for throttled reads, but it's less direct than ThrottledRequests.

Answer

SuccessfulRequestLatency

Answer

ReadThrottleEvents

Answer

ConsumedWriteCapacityUnits

Question 20

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.