DBS-C01 Practice Test 43 — 15 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?

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

Accepted Answer

Offload SELECT queries to the read replica. Offloading SELECT queries to the read replica reduces CPU utilization on the primary instance because read replicas can handle read traffic independently. Option A is incorrect: failing over to the standby instance does not reduce CPU load—the standby is only for high availability and becomes the new primary, still handling the same workload. Option B is incorrect: increasing the DB instance size would help but is not the best first step; it involves scaling costs and potential downtime, whereas using a read replica is more efficient and cost-effective for read-heavy workloads. Option C is incorrect: converting the read replica to a Multi-AZ standby would make it a synchronous replica for failover, not for offloading reads, so it would not reduce CPU on the primary.

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 developer executed a DELETE statement without a WHERE clause on an Amazon RDS for PostgreSQL instance. The transaction is still open. Which action should the developer take to undo the DELETE without affecting other operations?

Accepted Answer

Execute ROLLBACK in the same session.. The correct action is to execute ROLLBACK in the same session. Since the transaction is still open, issuing ROLLBACK will undo the DELETE statement without affecting other operations. Option A is incorrect because COMMIT would make the DELETE permanent. Option B is incorrect because Point-in-Time Recovery restores the entire DB instance to a past state, which is unnecessary and affects other data. Option D is incorrect because stopping and restoring from a snapshot would also affect other data and is not the simplest solution.

Answer

Execute COMMIT and then run a recovery script.

Answer

Use the Point-in-Time Recovery feature to restore the database to a time before the DELETE.

Answer

Stop the DB instance and restore from the latest snapshot.

Question 3

Which TWO metrics should be monitored to detect a memory leak in an RDS for Oracle instance? (Choose 2.)

Accepted Answer

SwapUsage. Options A and B are correct because FreeableMemory shows the available memory, and SwapUsage indicates when the OS uses swap due to memory pressure, which are both signs of a memory leak. Option C is wrong because DatabaseConnections does not directly indicate a memory leak. Option D is wrong because CPUUtilization may be high but is not specific to a memory leak. Option E is wrong because ReadIOPS relates to I/O, not memory.

Answer

DatabaseConnections

Answer

CPUUtilization

Answer

ReadIOPS

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. Long-running transactions on the writer instance hold locks for extended periods, increasing the probability of lock contention and deadlocks. Option A is incorrect because Performance Insights is a monitoring tool and does not cause locks or deadlocks. Option B is incorrect because mismatched instance sizes may affect performance but do not directly cause locks or deadlocks. Option D is incorrect because Aurora read replicas are read-only and cannot perform write operations.

Answer

Performance Insights is enabled

Answer

The writer and reader instances are of different sizes

Answer

Read replicas are performing write operations

Question 5

A company has an Amazon Aurora MySQL DB cluster with one writer and two readers. The application is reporting increased read latency. The DB cluster is using Aurora Auto Scaling for readers. Which metric should be used to trigger scaling out readers?

Accepted Answer

AverageActiveConnections. Aurora Auto Scaling for readers uses the 'AverageActiveConnections' metric to determine when to add readers. Option D is correct. Option A is incorrect because average active connections is the trigger, not read latency. Option B is incorrect because ReaderNodeCPU is not a predefined metric for auto scaling. Option C is incorrect because CPUUtilization is not the metric used for reader scaling.

Answer

ReadLatency

Answer

ReaderNodeCPU

Answer

CPUUtilization

Question 6

A company is deploying an RDS MySQL database using the above CloudFormation template. After deployment, the database automatically reboots during the maintenance window. The company wants to reduce the impact of maintenance events. Which parameter change would minimize unavailability?

Accepted Answer

Set AutoMinorVersionUpgrade to true in the template.. Setting AutoMinorVersionUpgrade to true ensures that minor version upgrades are applied automatically during the maintenance window. This prevents the need for a separate, manually scheduled maintenance event to apply these upgrades, thereby reducing the overall number of maintenance-related reboots and minimizing unavailability compared to the other options. Option B increases recovery points but does not reduce downtime; Option C improves performance but not maintenance impact; Option D shifts the downtime but does not reduce its length.

Answer

Increase BackupRetentionPeriod to 30 days to have more recovery points.

Answer

Increase AllocatedStorage to 500 GB to improve performance during maintenance.

Answer

Change PreferredMaintenanceWindow to a less busy time.

Question 7

A company is running a MongoDB database on Amazon EC2. The database is experiencing high disk I/O latency. Which AWS service can be used to monitor the disk I/O metrics at the instance level?

Accepted Answer

Amazon CloudWatch. Amazon CloudWatch provides disk I/O metrics for EC2 instances. Option A is wrong because Amazon RDS is a managed database service. Option C is wrong because Amazon DynamoDB is a NoSQL database service. Option D is wrong because Amazon S3 is an object storage service.

Answer

Amazon RDS

Answer

Amazon DynamoDB

Answer

Amazon S3

Question 8

A company is running a production Amazon RDS for MySQL DB instance. The database size is 500 GB and the workload is write-heavy. The team notices that the automated backups are taking longer than expected and are impacting the performance during the backup window. Which action should be taken to minimize the performance impact?

Accepted Answer

Create a read replica and configure automated backups on the replica.. Creating a read replica and configuring automated backups on the replica offloads the backup process from the primary DB instance. Since the workload is write-heavy, this minimizes the performance impact on the primary during the backup window. Option A is incorrect because disabling automated backups removes the ability to perform point-in-time recovery, which is risky for a production database. Option C is incorrect because increasing the DB instance size may improve backup speed but does not eliminate the performance impact on the primary instance, and it adds unnecessary cost. Option D is incorrect because moving the backup window to a low workload time does not reduce the performance impact during that window; it only changes when the impact occurs, and the workload may still be significant.

Answer

Disable automated backups and rely on manual snapshots taken during off-peak hours.

Answer

Increase the DB instance size to improve backup performance.

Answer

Move the backup window to a time when the workload is lowest.

Question 9

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 in DynamoDB adjusts capacity based on consumed capacity relative to provisioned capacity. With a target utilization of 70%, the expected consumed capacity for 10,000 RCU is 7,000 RCU. However, the actual consumed capacity is 8,000 RCU, which is 80% utilization, above the target. Auto scaling should normally increase capacity to bring utilization back to 70%. But if the auto scaling configuration has a maximum read capacity limit (e.g., 8,000 RCU), scaling cannot exceed that limit, explaining why capacity does not increase. Option A is incorrect because auto scaling can trigger even before throttling occurs. Option C is incorrect because auto scaling can increase both read and write capacity. Option D is incorrect because auto scaling scales based on sustained consumption above target utilization, not necessarily exceeding provisioned capacity.

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 10

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 11

A team is using Amazon DynamoDB with auto scaling enabled. They notice that some requests are returning ProvisionedThroughputExceededException errors during a sudden traffic spike. The application uses strong consistent reads. Which two actions would help mitigate the throttling without over-provisioning capacity? (Choose two.)

Accepted Answer

Implement DynamoDB Accelerator (DAX) to cache read results.. DAX acts as an in-memory cache for DynamoDB, reducing the number of read requests that consume provisioned throughput, thus mitigating throttling without increasing capacity. Option B is correct because adaptive capacity enables DynamoDB to automatically use unused throughput from other partitions to absorb traffic spikes, reducing ProvisionedThroughputExceededException errors. Option C is wrong because while eventually consistent reads consume half the read capacity, the application uses strong consistent reads, which may be required for data consistency, and this switch may not be acceptable. Option D is wrong because disabling auto scaling and manually setting higher capacity would lead to over-provisioning and increased cost, contrary to the goal of mitigating throttling without over-provisioning. Option E is wrong because burst capacity is limited and not guaranteed; it can handle short spikes but is not a reliable mitigation for sudden spikes.

Answer

Switch to eventually consistent reads for all queries.

Answer

Disable auto scaling and manually set higher capacity.

Answer

Use DynamoDB burst capacity for the spike.

Question 12

A company is using Amazon DynamoDB with a global table for a multi-region application. The application is deployed in us-east-1 and eu-west-1. The company notices that write latency to eu-west-1 is higher than expected. Which TWO actions can reduce write latency? (Choose TWO.)

Accepted Answer

Use DynamoDB Accelerator (DAX) for write caching.. DAX can be used as a write-through cache for DynamoDB, reducing write latency by caching writes locally and asynchronously flushing to the primary table. Option B is correct because writing to the local region (e.g., us-east-1) and allowing global tables replication to eu-west-1 reduces the latency for the local write operation; the replication happens asynchronously. Option C is incorrect because strongly consistent reads do not affect write operations. Option D is incorrect because using a single-region table in eu-west-1 would eliminate the multi-region capability and manual replication adds complexity and potential latency. Option E is incorrect because increasing write capacity does not reduce latency; it increases throughput but not speed.

Answer

Use strongly consistent reads in the application.

Answer

Use a single-region table in eu-west-1 and replicate data manually.

Answer

Increase the write capacity of the table in eu-west-1.

Question 13

A financial services company stores sensitive data in an Amazon DynamoDB table. The security team requires that all data at rest be encrypted with a customer-managed key that is rotated automatically every 12 months. The company also needs to audit key usage. Which solution meets these requirements?

Accepted Answer

Enable encryption at rest using an AWS KMS customer-managed CMK. Configure automatic key rotation with a 12-month period. Use AWS CloudTrail to audit key usage.. DynamoDB supports encryption at rest with AWS KMS customer-managed CMKs. Automatic key rotation every 12 months is a feature of KMS for CMKs. CloudTrail logs KMS API calls for auditing. Option A is incorrect because SSE-S3 is for S3, not DynamoDB. Option B is incorrect because CloudHSM does not provide automatic key rotation every 12 months and requires application-side encryption. Option C is incorrect because the default DynamoDB encryption uses an AWS owned key, which is not customer-managed and rotates automatically every 3 years, not 12 months. Option D is correct: it uses a customer-managed CMK with yearly rotation and CloudTrail for auditing.

Answer

Use server-side encryption with S3-managed keys (SSE-S3) for the DynamoDB table.

Answer

Use AWS CloudHSM to generate and store the encryption key. Configure the application to encrypt data before writing to DynamoDB.

Answer

Enable encryption at rest using the default DynamoDB encryption option (AWS owned key). Use AWS CloudTrail to audit key usage.

Question 14

A company uses Amazon DynamoDB with provisioned capacity for a gaming application. During a new game launch, write traffic spikes to 2x the provisioned write capacity for 30 minutes. Some writes are throttled. The company wants to handle these predictable spikes without manual intervention. What is the MOST cost-effective solution?

Accepted Answer

Enable DynamoDB auto scaling with a target utilization of 70%.. DynamoDB auto scaling automatically adjusts provisioned capacity based on actual usage, handling predictable spikes without manual intervention while minimizing cost by scaling down when demand drops. Option A is wrong because permanently doubling capacity leads to wasted resources and higher costs. Option B is wrong because on-demand mode can be more expensive for predictable workloads with consistent baseline traffic. Option D is wrong because SQS buffers writes but does not directly address DynamoDB write throttling; it adds latency and complexity without solving the capacity issue.

Answer

Increase the provisioned write capacity to 2x the baseline permanently.

Answer

Change the table to on-demand capacity mode.

Answer

Use Amazon SQS to buffer writes and process them later.

Question 15

A company is using Amazon ElastiCache for Redis to cache database query results. They notice that the cache hit ratio is low and many requests are hitting the database. The 'Evictions' metric is high. What is the MOST likely cause?

Accepted Answer

The cache node is too small for the workload.. The high 'Evictions' metric indicates that the cache node is constantly full, causing it to evict old data to make room for new data. This leads to a low cache hit ratio because frequently accessed items are evicted and must be fetched from the database. Option D correctly identifies that the cache node is too small for the workload. Option A is incorrect because insufficient replication factor would affect availability, not evictions. Option B is incorrect because encryption in transit does not impact cache capacity or evictions. Option C is incorrect because high network latency would affect request latency but not directly cause evictions.

Answer

The replication factor is insufficient.

Answer

Encryption in transit is enabled.

Answer

The application is experiencing high network latency.