DBS-C01 Practice Test 45 — 15 Questions

Question 1

A company is running a production Amazon RDS for PostgreSQL database. The database has experienced a sudden spike in CPU utilization, causing application timeouts. The monitoring team needs to identify the root cause. Which AWS service or feature should be used to analyze the database load and identify the specific queries causing the high CPU?

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

Accepted Answer

Amazon RDS Performance Insights. (Amazon RDS Performance Insights) is correct because it provides a database performance tuning and monitoring feature that helps quickly assess the load on your database and identify specific queries causing high CPU utilization. Option A (Enhanced Monitoring) is wrong because it provides OS-level metrics, not database query details. Option B (Amazon CloudWatch Logs) is wrong because it captures database logs, not real-time performance data. Option D (AWS Trusted Advisor) is wrong because it provides best practice checks but not query-level analysis.

Answer

Enhanced Monitoring

Answer

Amazon CloudWatch Logs

Answer

AWS Trusted Advisor

Question 2

A company is using Amazon DynamoDB for a high-traffic application. The application is experiencing intermittent `ProvisionedThroughputExceededException` errors. The team has already increased the read and write capacity units multiple times but the errors persist. Which of the following is the MOST likely cause of the issue?

Accepted Answer

A hot key or uneven partition access pattern is causing throttling. Hot keys or uneven partition access patterns can cause throttling even if overall provisioned capacity appears sufficient. Option A is wrong because DynamoDB Accelerator (DAX) is an in-memory cache that reduces read load, but it does not directly fix capacity exceeded errors; misconfiguration might cause cache misses but not ProvisionedThroughputExceededException. Option B is wrong because Global Tables replication does not cause throttling on the source table; conflicts are handled by last-writer-wins. Option C is wrong because increasing capacity units multiple times without resolving the underlying access pattern suggests the issue is not simply insufficient capacity.

Answer

DynamoDB Accelerator (DAX) is not properly configured

Answer

The table is part of a DynamoDB Global Table and replication is causing conflicts

Answer

The provisioned capacity is not increased enough

Question 3

A company is using Amazon DynamoDB with server-side encryption enabled. They need to ensure that all access to the table is audited. Which service should be used to capture data-plane API calls?

Accepted Answer

AWS CloudTrail. AWS CloudTrail, when configured to capture data events, can record DynamoDB data-plane API calls such as GetItem and PutItem. Option A (VPC Flow Logs) captures network traffic, not API calls. Option B (AWS Config) records configuration changes, not data-plane actions. Option C (Amazon CloudWatch Logs) can store logs but does not directly capture API calls; it would require another service to send logs to it.

Answer

VPC Flow Logs

Answer

AWS Config

Answer

Amazon CloudWatch Logs

Question 4

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.. A low cache hit ratio and high cache miss ratio indicate that the cache is not storing data that is frequently requested. The most likely cause is that the Time-To-Live (TTL) for cache keys is set too short, causing data to be evicted before it can be reused. Option A is incorrect because read replicas improve read scalability but do not directly affect cache hit ratio. Option B is incorrect because write capacity is not relevant for a caching layer that primarily serves reads. Option C is incorrect: while high CPU utilization can cause latency, it would not specifically cause low cache hits and high misses.

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 5

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.. Amazon RDS Performance Insights provides detailed database performance metrics and helps identify the specific queries contributing to high CPU utilization, enabling targeted optimization. Option A is incorrect because increasing instance size is a reactive scaling action rather than a diagnostic step; it does not identify the root cause. Option C is incorrect because Multi-AZ deployment is designed for high availability and failover, not for distributing load or improving performance. Option D is incorrect because disabling slow query logging removes valuable diagnostic information that could help identify problematic queries.

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 6

A company uses Amazon Aurora MySQL. They notice that the DB cluster's failover took longer than expected during a recent primary instance failure. CloudWatch shows Failover latency of 120 seconds. Which configuration change would most likely reduce the failover time?

Accepted Answer

Configure the application to use the cluster endpoint with Aurora JDBC driver's fast failover feature.. Configuring the application to use the cluster endpoint with the Aurora JDBC driver's fast failover feature allows the driver to quickly detect the new writer after a failover and reconnect, significantly reducing the perceived failover time by avoiding DNS propagation delays. Option A is incorrect because increasing the instance class improves performance but does not affect failover speed. Option B is incorrect because backup retention period is unrelated to failover latency. Option C is incorrect because Aurora MySQL is already Multi-AZ by design; enabling Multi-AZ is not a separate configuration step.

Answer

Increase the instance class of the primary and replica instances.

Answer

Increase the backup retention period to 35 days.

Answer

Enable Multi-AZ on the DB cluster.

Question 7

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, D, and E are correct. Verifying DynamoDB Streams (A) ensures that change data capture is enabled for replication. Reviewing DynamoDB Streams error logs in CloudWatch Logs (D) helps identify replication errors. Checking the ReplicationLatency metric (E) reveals if there is replication lag. Option B is not a diagnostic step; disabling and re-enabling global tables is disruptive and not recommended. Option C is incorrect because increasing write capacity on the secondary table does not address consistency issues; replication depends on streams and network, not write capacity.

Answer

Disable and re-enable global tables to force resync.

Answer

Increase the write capacity on the secondary table.

Question 8

A company is running an Amazon RDS for MySQL Multi-AZ DB instance. The application experiences a brief write disruption during automatic failover. The database workload has low write latency requirements. Which configuration change would minimize application impact during failover?

Accepted Answer

Change the DB instance to use a Multi-AZ DB cluster configuration.. Changing to a Multi-AZ DB cluster (option B) reduces application impact during failover because it uses a writer and two reader instances in separate Availability Zones. Failover to a reader is typically faster than the standard Multi-AZ standby failover, minimizing write disruption. Option A (promoting a read replica) is not automatic and introduces significant delay. Option C (single-AZ with backups) does not address failover impact. Option D (increasing instance class) does not significantly reduce failover time.

Answer

Create a read replica in a different Availability Zone and promote it during failover.

Answer

Use a single-AZ deployment and rely on automated backups for recovery.

Answer

Increase the DB instance class to reduce failover time.

Question 9

A company is designing a multi-tier application that uses Amazon RDS for PostgreSQL. The application must encrypt data at rest and in transit. Which combination of steps should be taken to meet these requirements? (Choose the single best answer.)

Accepted Answer

Enable encryption at rest when launching the RDS instance, and configure the DB parameter group to require SSL connections.. Amazon RDS for PostgreSQL supports encryption at rest only when enabled at instance launch, and SSL/TLS encryption in transit is enforced by configuring the DB parameter group to require SSL connections (e.g., setting `rds.force_ssl=1`). Encryption at rest cannot be added after creation, and SSL ensures data is encrypted between the application and the database.

Answer

Use client-side encryption for data before sending to RDS, and enable encryption at rest after the instance is created.

Answer

Launch the RDS instance without encryption, then enable encryption at rest using the AWS Console.

Answer

Use AWS KMS to encrypt the connection between the application and RDS.

Question 10

A company is using Amazon DynamoDB as the primary database for a global e-commerce application. During the holiday season, the application experiences throttling on write requests even though the read and write capacity units are well below the provisioned limits. The table uses on-demand capacity mode. What is the most likely cause of this throttling?

Accepted Answer

There is a hot partition due to an uneven write distribution across partition keys.. In DynamoDB on-demand capacity mode, throughput scales automatically based on traffic. However, throttling can still occur if a single partition receives more write requests than the partition's maximum throughput capacity (1,000 WCU per partition). This is known as a hot partition, caused by an uneven distribution of write activity across partition keys. Option A correctly identifies this. Option B is incorrect because on-demand mode does not use provisioned capacity. Option C uses incorrect terminology—there is no 'maximum write capacity units per partition' that the table as a whole can exceed. Option D is incorrect because DynamoDB does not have a per-region account-level write limit that causes throttling on a single table.

Answer

The table's provisioned write capacity is set too low.

Answer

The table has exceeded the maximum write capacity units per partition.

Answer

The AWS account has reached the DynamoDB write throughput limit per region.

Question 11

A database administrator is reviewing the configuration of an RDS MySQL instance. Based on the exhibit, which change would MOST improve the database's performance under heavy write workloads without increasing costs significantly?

Accepted Answer

Change the storage type from gp2 to gp3 to get higher baseline IOPS and throughput.. Gp3 storage provides higher baseline IOPS and throughput than gp2 at the same cost, which directly improves performance under heavy write workloads. Option A is incorrect because parameter group tuning can help but is not the most impactful change without additional cost. Option B is incorrect because backup retention period does not affect performance. Option C is incorrect because Multi-AZ provides high availability, not improved write performance.

Answer

Change the DB parameter group to a custom one with optimized MySQL parameters.

Answer

Increase the backup retention period to 35 days to improve performance.

Answer

Enable Multi-AZ to improve write performance.

Question 12

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 13

A database specialist is investigating a sudden increase in Amazon RDS for PostgreSQL connections. The DB instance's CloudWatch metric DatabaseConnections shows a spike from 100 to 500 within minutes. The application connects using a connection pool. Which step should the specialist take first to mitigate the issue while preserving application availability?

Accepted Answer

Modify the DB parameter group to reduce the max_connections value and reboot the instance to apply changes.. Reducing the max_connections value in the DB parameter group and rebooting the instance will limit the number of concurrent connections, preventing the database from being overwhelmed. This is the fastest way to mitigate the spike while preserving application availability. Option A is wrong because terminating all connections and restarting the database would disrupt the application. Option B is wrong because modifying the security group does not affect the number of connections, only the allowed sources. Option C is wrong because increasing the instance size may take time to provision and does not immediately address the connection spike.

Answer

Use the RDS console to terminate all active connections and then restart the database.

Answer

Modify the security group to restrict inbound traffic to the database.

Answer

Increase the DB instance size to handle more connections.

Question 14

Which TWO tools can be used to monitor query performance in Amazon Aurora MySQL? (Choose 2.)

Accepted Answer

Amazon RDS Performance Insights. A is correct: Amazon RDS Performance Insights provides a visualization of database performance, including metrics like average active sessions, which helps identify query performance issues. C is correct: Amazon RDS Enhanced Monitoring provides OS-level metrics such as CPU, memory, and disk I/O, which can help correlate with query performance. B is incorrect: AWS Config is a service for configuration audit and compliance, not for real-time performance monitoring. D is incorrect: VPC Flow Logs capture network traffic metadata and are not specific to query performance. E is incorrect: AWS CloudTrail logs API calls for governance and compliance, not database query performance.

Answer

AWS Config

Answer

VPC Flow Logs

Answer

AWS CloudTrail

Question 15

Which TWO metrics should be monitored to detect an Amazon RDS for MySQL instance that is experiencing memory pressure? (Choose 2.)

Accepted Answer

SwapUsage. A and D are correct. SwapUsage directly indicates memory pressure when it exceeds 0, as the operating system swaps memory to disk. FreeableMemory shows the amount of available memory, so a low value suggests memory pressure. B (DatabaseConnections) is incorrect because it is an indirect indicator that can affect memory but is not a direct memory metric. C (ReadIOPS) is disk I/O, not memory. E (CPUUtilization) is CPU usage, not memory.

Answer

DatabaseConnections

Answer

ReadIOPS

Answer

CPUUtilization