DBS-C01 Monitoring and Troubleshooting Practice Test 17 — 15 Questions

Question 1

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.. The most likely cause is that the security group does not allow inbound traffic on port 5432 from the client IP, causing a timeout. Option A is incorrect because the endpoint is correctly provided by AWS; an incorrect endpoint would produce a different error. Option B is incorrect because SSL encryption is not required by default; if it were, the error would be an SSL handshake failure, not a timeout. Option D is incorrect because Multi-AZ configurations use the same endpoint; no separate endpoint is needed.

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 2

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.. AuroraReplicaLagMaximum measures the maximum lag between the writer and any reader. If the reader is undersized, it cannot apply changes as fast as the writer generates them, so increasing the reader instance size provides more CPU and memory to reduce lag. This directly addresses the bottleneck on the replica side.

Answer

Increase the instance size of the writer.

Answer

Reduce the number of transactions per second.

Answer

Enable Multi-AZ on the cluster.

Question 3

A database administrator notices that an Amazon RDS for MySQL instance is using 100% of its allocated storage. Which action should be taken first to prevent the instance from becoming inaccessible?

Accepted Answer

Modify the DB instance to increase allocated storage.. When an RDS instance is at 100% storage, the immediate priority is to prevent the instance from becoming inaccessible, and RDS supports increasing allocated storage on a running instance without downtime (for most engines and storage types). Modifying the DB instance to increase allocated storage is the fastest, safest first action and can be done online. Other actions like snapshots or log deletion do not relieve the immediate pressure.

Answer

Create a snapshot and archive it to Amazon S3.

Answer

Delete old binary logs to free up space.

Answer

Reboot the DB instance.

Question 4

A company uses Amazon CloudWatch to monitor an RDS for Oracle instance. They want to receive an alert when the database connection count exceeds 90% of the maximum connections. Which CloudWatch metric should be used to create the alarm?

Accepted Answer

DatabaseConnections. The DatabaseConnections metric in CloudWatch reports the number of client connections to the RDS instance. To alert when connections exceed 90% of the maximum, the administrator should create an alarm on DatabaseConnections with a threshold based on the instance's max_connections parameter. This metric directly reflects the connection count.

Answer

ActiveTransactions

Answer

ReadIOPS

Answer

NetworkThroughput

Question 5

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 6

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 7

A database administrator notices that an Amazon RDS for SQL Server DB instance has been in the 'storage-optimization' state for several hours after modifying the storage type from gp2 to io1. What should the administrator do to resolve this?

Accepted Answer

Wait for the storage optimization to complete.. The 'storage-optimization' state indicates that RDS is performing a background storage modification, such as changing storage type or increasing allocated storage. This is a normal, expected state and the administrator should simply wait for it to complete. The modification is applied asynchronously, and the DB instance remains available during the process, though performance may be slightly impacted. Attempting to cancel or reboot will not speed up the process and could cause issues.

Answer

Restore from the latest snapshot and reapply the modification.

Answer

Cancel the modification by modifying the DB instance back to gp2.

Answer

Reboot the DB instance.

Question 8

A development team is using Amazon RDS for MySQL with read replicas to offload reporting queries. They notice that the read replica is consistently lagging behind the primary by several seconds. The primary handles 5000 writes per second. Which action would most likely reduce replica lag?

Accepted Answer

Increase the instance size of the read replica.. Increasing the instance size of the read replica provides more CPU and memory resources, allowing it to apply changes from the binary log faster, thereby reducing replica lag. Option A is incorrect because increasing 'max_connections' on the primary does not affect the replica's ability to apply changes; it only allows more connections to the primary. Option C is incorrect because disabling binary logging on the primary would break replication entirely, as the replica relies on the binary log to receive changes. Option D is incorrect because converting the primary to Multi-AZ improves availability and failover but does not directly reduce replication lag on the read replica.

Answer

Increase the 'max_connections' parameter on the primary instance.

Answer

Disable binary logging on the primary instance to reduce I/O.

Answer

Convert the primary instance to a Multi-AZ deployment.

Question 9

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.. When an option group modification requires a reboot, the DB instance remains in the 'modifying' state until the reboot is applied. For RDS for Oracle, adding certain options like OEM requires a reboot to take effect, so the team should reboot the DB instance to complete the modification. This is documented AWS behavior for options that have the 'requires reboot' attribute.

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 10

An administrator is troubleshooting an Amazon RDS for PostgreSQL instance that is experiencing high CPU utilization. The administrator has enabled Performance Insights. Which metric should be examined first to identify the queries consuming the most CPU?

Accepted Answer

db.load.avg. Performance Insights uses db.load.avg as its core metric, which represents the average number of active sessions (Average Active Sessions, or AAS) broken down by wait events, SQL statements, users, and hosts. When CPU is the bottleneck, db.load.avg filtered by the CPU wait event immediately shows which SQL statements are consuming the most CPU. This is the correct first metric to examine.

Answer

db.sessions

Answer

db.cpu.avg

Answer

db.bytes_sent

Question 11

Which TWO AWS services can be used to monitor the performance of an Amazon DynamoDB table and send alerts when throttling occurs? (Choose two.)

Accepted Answer

Amazon CloudWatch Alarms. Amazon CloudWatch [CORRECT] is the AWS monitoring service that natively collects DynamoDB metrics such as ThrottledRequests, ConsumedReadCapacityUnits, and ConsumedWriteCapacityUnits, so it is the foundational service for observing table performance. Amazon CloudWatch Alarms [CORRECT] builds on those metrics by letting you define thresholds (for example, ThrottledRequests > 0 over a period) and trigger actions like Amazon SNS notifications when throttling is detected. Together they provide the metric collection and alerting needed for this scenario. Amazon Inspector is a vulnerability management service for EC2 and container workloads, not a performance monitoring or alerting tool for DynamoDB. VPC Flow Logs capture IP traffic metadata at the ENI level and do not expose DynamoDB capacity or throttling metrics. AWS Config records resource configuration changes and evaluates compliance rules, but it does not monitor DynamoDB performance metrics or send throttling alerts.

Answer

Amazon Inspector

Answer

VPC Flow Logs

Answer

AWS Config

Question 12

A company is running a production Amazon RDS for MySQL DB instance. The application team reports intermittent high latency and connection timeouts. A quick check shows that the DB instance's CPU utilization is consistently above 90% during peak hours. The database size is 500 GB and the instance class is db.r5.large. Which combination of actions should a database specialist take to resolve the performance issue?

Accepted Answer

Scale up the DB instance to db.r5.xlarge and review slow query logs to optimize poorly performing queries.. Sustained CPU above 90% on a db.r5.large indicates the instance class is undersized for the workload, so scaling up to db.r5.xlarge doubles vCPU and memory to relieve the bottleneck. Pairing that with slow query log review addresses the root cause — inefficient queries that consume disproportionate CPU — which is the standard RDS performance troubleshooting pattern.

Answer

Increase the allocated storage to 1 TB and enable auto-scaling for storage.

Answer

Enable Multi-AZ and increase the allocated storage to 1 TB to improve I/O performance.

Answer

Enable Performance Insights and create a CloudWatch alarm to notify when CPU exceeds 80%.

Question 13

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.. Increased latency in DynamoDB can be caused by hot partitions where many requests hit the same partition, leading to throttling even with on-demand capacity if the partition limits are exceeded. Checking CloudWatch metrics for throttled requests and partition metrics helps identify hot partitions. Option A is incorrect because adding a GSI does not improve UpdateItem performance; it only helps query performance. Option B is incorrect: on-demand mode already handles capacity, and increasing read capacity units does not affect write operations like UpdateItem. Option C is incorrect: disabling conditional writes would break the application's concurrency control and does not guarantee latency reduction; condition evaluation is a fast, internal operation.

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 14

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. The 'Deadlocks' metric in Amazon RDS for SQL Server specifically counts the number of deadlocks that occur on the DB instance. Option A is incorrect because 'BlockedTransactions' tracks transactions that are blocked, not deadlocks. Option C is incorrect because 'DatabaseConnections' is a count of active connections, not related to deadlocks. Option D is incorrect because 'LockWaits' measures the number of lock waits, which is a different contention event.

Answer

BlockedTransactions

Answer

DatabaseConnections

Answer

LockWaits

Question 15

A company is using Amazon Redshift for data warehousing. The data engineering team notices that queries are taking longer than expected. The cluster has two nodes of type dc2.large. The database specialist checks the system tables and finds that many queries are using the disk for temporary storage. Which action should the specialist take to improve query performance?

Accepted Answer

Upgrade the cluster to a node type with more memory, such as ra3.xlplus.. Queries spilling to disk for temporary storage indicate insufficient memory for the working set, causing Redshift to write intermediate results to disk and slowing performance. Upgrading to a node type with more memory per node (such as ra3.xlplus, which offers more memory and managed storage) directly addresses this bottleneck. Adding nodes or distribution keys helps with data skew and parallelism but does not fix memory pressure that forces disk spills.

Answer

Add distribution keys to the tables to improve data distribution.

Answer

Enable concurrency scaling to offload queries to additional clusters.

Answer

Increase the number of nodes to three to distribute the workload.