DBS-C01 Practice Exam 61 — 20 Questions

Question 1

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.. Option C is correct because reducing the maximum connections in the parameter group and rebooting immediately limits the active connections, preventing the database from being overwhelmed. Option A is wrong because modifying the security group does not affect the number of connections. Option B is wrong because increasing the instance size may help but takes time to provision. Option D is wrong because terminating all connections will disrupt the application.

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 2

A company is using Amazon Neptune and notices that some queries are slow. The DBA wants to identify which queries consume the most time. Which feature should be used?

Accepted Answer

Query profiler. Neptune's query profiler provides detailed information about query execution time. The slow query log only logs queries that exceed a threshold. The audit log is for security events. The performance insights is for RDS, not Neptune.

Answer

Database audit log

Answer

Slow query log

Answer

Performance Insights

Question 3

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

Accepted Answer

Amazon RDS Performance Insights. A and D are correct. Performance Insights provides database performance analysis. Enhanced Monitoring provides OS-level metrics. B is wrong because CloudTrail logs API calls. C is wrong because VPC Flow Logs show network traffic. E is wrong because AWS Config tracks resource configuration.

Answer

AWS Config

Answer

VPC Flow Logs

Answer

AWS CloudTrail

Question 4

A developer is receiving timeout errors when connecting to an Amazon ElastiCache for Redis cluster from an Amazon EC2 instance. The security group for the EC2 instance allows outbound traffic to the Redis cluster's security group on port 6379. The Redis cluster's security group does not allow inbound traffic from the EC2 instance. What is the most likely cause of the timeout?

Accepted Answer

The Redis cluster security group does not have an inbound rule allowing traffic from the EC2 security group on port 6379. Option A is correct because security groups are stateful; for inbound traffic, the target security group must allow the incoming connection. Option B is incorrect because the subnet routing does not block specific ports. Option C is incorrect because NACLs are stateless but the issue is with security groups. Option D is incorrect because the Redis cluster is in a VPC, not on-premises.

Answer

The network ACL for the Redis subnet is blocking inbound traffic on port 6379

Answer

The subnet route table does not have a route to the Redis cluster

Answer

The Redis cluster is not accessible from within the same VPC

Question 5

A developer is trying to connect to an RDS for PostgreSQL instance using the endpoint shown in the exhibit. The connection fails with a timeout. Which of the following is the most likely cause?

Accepted Answer

The security group does not allow inbound traffic on port 5432 from the client IP.. Option B is correct because the port 5432 is the default PostgreSQL port, but the security group may not allow inbound traffic on that port. Option A is wrong because the endpoint is correct. Option C is wrong because Multi-AZ does not affect connectivity. Option D is wrong because there is no encryption requirement implied.

Answer

The endpoint address is incorrect.

Answer

The DB instance requires SSL encryption to connect.

Answer

The DB instance is in a Multi-AZ configuration and requires a different endpoint.

Question 6

A developer receives a 'ResourceNotFoundException' when trying to describe a DynamoDB table. The developer runs the command shown in the exhibit and gets the output. What is the most likely cause?

Accepted Answer

The developer is using a different AWS region or the table name has incorrect case.. Option C is correct because the table is in us-west-2, but the developer may be querying from a different region or the table name is case-sensitive. Option A is wrong because the table is ACTIVE. Option B is wrong because the ARN is present. Option D is wrong because the command succeeded.

Answer

The table is not in ACTIVE state.

Answer

The table ARN is incorrect.

Answer

The developer does not have permission to describe the table.

Question 7

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.. Option D is correct because on-demand capacity mode automatically scales but can throttle if traffic is unevenly distributed across partitions, leading to hot partitions. Option A is incorrect because on-demand mode does not have a per-table limit in the same way provisioned capacity does. Option B is incorrect because DynamoDB does not have a global write limit per account that would cause throttling on a single table. Option C is incorrect because the table uses on-demand capacity mode, not provisioned.

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 8

Which TWO actions can help reduce Amazon RDS for MySQL replication lag between a primary instance and a read replica? (Choose two.)

Accepted Answer

Reduce the number of write-heavy DML statements on the primary.. Options A and D are correct. Increasing the replica instance size gives it more resources to apply changes. Reducing write-heavy DML on the primary reduces the volume of changes to replicate. Option B is incorrect because enabling Multi-AZ on the primary does not reduce lag. Option C is incorrect because binary logging is required for replication. Option E is incorrect because increasing the replica's allocated storage does not directly reduce lag.

Answer

Increase the allocated storage for the read replica.

Answer

Enable Multi-AZ on the primary instance.

Answer

Disable binary logging on the primary instance.

Question 9

Refer to the exhibit. A database administrator retrieves CloudWatch metrics for an RDS instance. What is the trend of CPU utilization during the monitored period?

Accepted Answer

CPU utilization is increasing over time.. Option B is correct. The average CPU utilization increases from 75.5% to 98.2% over the hour, indicating a steady increase. Option A is incorrect because it is not decreasing. Option C is incorrect because it is not constant. Option D is incorrect because it does not fluctuate; it increases monotonically.

Answer

CPU utilization is decreasing over time.

Answer

CPU utilization is constant around 90%.

Answer

CPU utilization fluctuates randomly.

Question 10

Refer to the exhibit. A developer runs the AWS CLI command and receives the output shown. What is this output?

Accepted Answer

The DNS endpoint of the DB instance. Option C is correct. The output is the DNS endpoint of the RDS instance. Option A is wrong because it's not an IP address. Option B is wrong because Resource ID looks different. Option D is wrong because the reader endpoint includes '-ro'.

Answer

The private IP address of the DB instance

Answer

The reader endpoint of a Multi-AZ cluster

Answer

The resource ID of the DB instance

Question 11

A team is using Amazon DynamoDB Accelerator (DAX) to improve read performance for a table. They notice that DAX is returning stale data even though the TTL is set to 5 minutes. The table is updated frequently by multiple writers. What is the most likely cause of the stale reads?

Accepted Answer

The TTL is too long, causing cached items to remain after updates. Option B is correct because DAX uses a write-through cache; if the TTL is too long, cached data may become stale before invalidation. Option A is incorrect because DAX supports eventual consistency and can return stale data if TTL is long. Option C is incorrect because DAX cache is not sharded across nodes in the same cluster. Option D is incorrect because DAX does not have a separate cache for each AZ.

Answer

The DAX cluster is not large enough to cache all items, causing cache misses

Answer

DAX is configured with eventual consistency, which returns stale data by design

Answer

The DAX cluster is deployed in a different Availability Zone than the application

Question 12

A database specialist needs to monitor the number of deadlocks occurring in an Amazon RDS for SQL Server DB instance. Which CloudWatch metric should be used?

Accepted Answer

Deadlocks. Option A is correct because Deadlocks is a specific metric in Amazon RDS for SQL Server that tracks deadlock occurrences. Option B is wrong because it is a generic metric. Option C is wrong because it is for blocking, not deadlocks. Option D is wrong because it is for lock waits.

Answer

BlockedTransactions

Answer

DatabaseConnections

Answer

LockWaits

Question 13

A company is monitoring an Amazon Aurora MySQL DB cluster. They observe that the AuroraReplicaLagMaximum metric is consistently above 10 seconds. Which action would best reduce the replica lag?

Accepted Answer

Increase the instance size of the reader.. Option B is correct because increasing the instance size of the reader can improve its ability to apply changes faster. Option A is wrong because increasing the writer size may not help if the reader is the bottleneck. Option C is wrong because reducing transaction size helps but may not be feasible. Option D is wrong because Multi-AZ is always enabled for Aurora.

Answer

Increase the instance size of the writer.

Answer

Reduce the number of transactions per second.

Answer

Enable Multi-AZ on the cluster.

Question 14

A team is using Amazon RDS for Oracle with an option group that includes the Oracle Enterprise Manager (OEM) option. After modifying the option group to add a new option, the DB instance is stuck in the 'modifying' state for an extended period. What should the team do?

Accepted Answer

Reboot the DB instance to complete the modification.. Option A is correct because adding certain options may require a reboot. Option B is incorrect because the option group modification is likely valid; the issue is that it requires a reboot. Option C is incorrect because modifying the DB instance again would not help. Option D is incorrect because the DB instance is not in a failed state.

Answer

Contact AWS Support to force the modification.

Answer

Create a new DB instance with the desired options and migrate the data.

Answer

Modify the DB instance again to reset the state.

Question 15

Refer to the exhibit. A database administrator runs the AWS CLI command to describe events for an RDS instance. Which conclusion is most likely correct based on the output?

Accepted Answer

The DB instance experienced a Multi-AZ failover and subsequently restarted.. Option C is correct. The output shows a failover event followed by a restart, which is typical after a failover. Option A is incorrect because the events show a failover, not a manual restart. Option B is incorrect because the failover was completed, not failed. Option D is incorrect because there is no indication of a snapshot restore.

Answer

The Multi-AZ failover failed and the instance restarted.

Answer

The DB instance was manually restarted by an administrator.

Answer

The DB instance was restored from a snapshot and then restarted.

Question 16

A company is using Amazon DynamoDB for a gaming leaderboard application. Recently, users have experienced increased latency when updating scores. The DynamoDB table has on-demand capacity mode. The application performs UpdateItem calls with a condition expression. Which action is most likely to reduce the latency?

Accepted Answer

Ensure that there are no throttled requests in the CloudWatch metrics and verify that the table is not experiencing hot partitions.. Option A is correct because with on-demand capacity, DynamoDB can handle sudden traffic spikes without throttling. Increasing read capacity is not applicable because on-demand mode automatically adjusts. Optimistic locking is already used implicitly with condition expressions. Adding a global secondary index does not directly reduce UpdateItem latency.

Answer

Add a global secondary index (GSI) with the score as the sort key to improve update performance.

Answer

Switch the table to provisioned capacity and increase the read capacity units to handle peak load.

Answer

Disable conditional writes to reduce the overhead of condition expression evaluation.

Question 17

A company is troubleshooting a performance issue with an Amazon RDS for MariaDB instance. The CloudWatch metric 'ReadIOPS' is consistently high, but 'WriteIOPS' is low. Which TWO actions could help improve read performance?

Accepted Answer

Add a read replica to offload read queries.. Adding a read replica offloads read traffic from the primary. Increasing the instance size can provide more memory for caching, reducing read IO. Option C (increasing storage) may help if it increases IOPS, but not necessarily. Option D (enabling Multi-AZ) does not improve read performance. Option E (using Amazon ElastiCache) is a valid approach but not specific to RDS.

Answer

Increase the allocated storage to improve IOPS.

Answer

Use Amazon ElastiCache to cache query results.

Answer

Enable Multi-AZ to improve read performance.

Question 18

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

Accepted Answer

SwapUsage. B and D are correct. SwapUsage indicates memory pressure when it exceeds 0. FreeableMemory shows available memory. A is wrong because CPUUtilization is CPU, not memory. C is wrong because DatabaseConnections affects memory but is indirect. E is wrong because ReadIOPS is disk I/O.

Answer

DatabaseConnections

Answer

ReadIOPS

Answer

CPUUtilization

Question 19

A company is using Amazon Redshift for data warehousing. The users report that queries are slow, and the CloudWatch metric 'CPUUtilization' shows high usage. The cluster has 4 dc2.large nodes. The administrator runs the following query: SELECT * FROM stl_query WHERE starttime > '2023-12-01' ORDER BY duration DESC LIMIT 10; This shows that the longest query runs for over 5 minutes. Which of the following is the MOST effective way to improve query performance?

Accepted Answer

Add more nodes to the cluster (scale out). Option C is correct because distributing data across more nodes allows parallel processing, which reduces query execution time. Option A is incorrect because the issue is CPU, not storage. Option B is incorrect because WLM queues manage concurrency, not individual query performance. Option D is incorrect because vacuum reclaims space but does not directly speed up queries.

Answer

Increase the size of the cluster volume by adding more storage

Answer

Run the VACUUM command to reclaim space and improve query performance

Answer

Modify the workload management (WLM) queue to increase concurrency

Question 20

A company is monitoring an Amazon RDS for Oracle instance. CloudWatch alarms show that FreeableMemory is consistently below 256 MB. The database has high read and write I/O. Which THREE steps should the database specialist take to diagnose the issue?

Accepted Answer

Check the MemoryPressure and LogFileSyncDuration metrics in CloudWatch.. Options A, C, and D are correct. Checking memory pressure (A), looking at swap usage (C), and reviewing memory advisor (D) are all appropriate. Option B is wrong because storage auto scaling does not address memory. Option E is wrong because RDS uses a fixed SGA/PGA, and increasing instance size might be a solution but not a diagnostic step.

Answer

Enable storage auto scaling to increase allocated storage.

Answer

Increase the DB instance class to allocate more memory.