DBS-C01 Monitoring and Troubleshooting Practice Test 2 — 15 Questions

Question 1

A database engineer is troubleshooting slow query performance on an Amazon RDS for PostgreSQL instance. The instance is db.r5.large with 500 GB of General Purpose SSD (gp2) storage. CloudWatch metrics show high Read Latency and high Read IOPS, but low CPU utilization. Which TWO actions should the engineer take to improve performance?

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

Accepted Answer

Create a read replica and offload read queries to it.. A is correct because creating a read replica offloads read queries from the primary instance, reducing the read IOPS and read latency on the primary. This directly addresses the high Read Latency and high Read IOPS metrics without requiring a larger instance class or storage change, especially since CPU utilization is low, indicating the bottleneck is I/O, not compute.

Answer

Increase the DB instance class to a larger size, such as db.r5.2xlarge.

Answer

Enable Multi-AZ to use the standby for read traffic.

Answer

Optimize queries by adding appropriate indexes.

Question 2

A company is using Amazon DynamoDB with autoscaling enabled. The table has a partition key of 'order_id' and a sort key of 'order_date'. The application performs both point queries and range queries. Recently, the 'ConsumedReadCapacityUnits' metric shows that the table is consistently using 100% of the provisioned capacity. Which THREE factors should the database engineer investigate to determine the cause?

Accepted Answer

Whether the application is using Scan operations instead of Query operations.. Scan operations read the entire table or index before applying filters, consuming far more read capacity than Query operations, which target specific partition and sort key values. If the application is using Scans instead of Queries, it would consistently consume 100% of provisioned capacity even for small result sets, leading to throttling and high utilization.

Answer

Whether autoscaling is configured correctly to add capacity.

Answer

Whether a global secondary index is being used for queries.

Question 3

A company is using Amazon RDS for MySQL and notices that database connections are being rejected intermittently. The application logs show 'Too many connections' errors. The DB instance has 1000 max_connections. Which action should the DBA take to troubleshoot and resolve this issue without impacting performance?

Accepted Answer

Enable Performance Insights and review the 'DB Connections' metric to identify spikes and troubleshoot application connection pooling. Enabling Performance Insights allows the DBA to monitor the 'DB Connections' metric in near real-time, identify exactly when connection spikes occur, and correlate those spikes with application behavior. This diagnostic approach pinpoints the root cause—such as a connection leak or insufficient connection pooling—without making changes that could degrade performance. Increasing max_connections or lowering wait_timeout without understanding the usage pattern can lead to resource exhaustion or premature connection termination.

Answer

Increase the max_connections parameter to 5000 in the DB parameter group

Answer

Create a read replica to offload read traffic

Answer

Set the 'wait_timeout' parameter to a lower value to close idle connections faster

Question 4

A database engineer is troubleshooting a production Amazon Aurora MySQL DB cluster. The application is experiencing high latency on write operations. The engineer checks the Amazon CloudWatch metrics and sees that the 'AuroraBinlogReplicaLag' metric is high. What is the most likely cause of the write latency?

Accepted Answer

The binlog replication to a downstream MySQL instance is falling behind. The 'AuroraBinlogReplicaLag' metric specifically measures the lag between the Aurora MySQL cluster and an external MySQL instance that is replicating from Aurora using binary log (binlog) replication. When this lag is high, it indicates that the downstream MySQL instance is falling behind in applying binlog events, which can cause write operations on the Aurora cluster to stall or slow down due to the synchronous nature of binlog generation and the need to retain binlogs until they are consumed by the replica.

Answer

The DB cluster has insufficient storage capacity for the binlog files

Answer

The DB cluster has a high CPU utilization that is causing replication lag

Answer

A recent failover event caused the binlog to be replayed from the last checkpoint

Question 5

A company is running a production Amazon DynamoDB table with on-demand capacity. The application is experiencing increased latency and throttled requests during peak hours. Which monitoring tool should the database specialist use to identify the specific partition keys causing the throttling?

Accepted Answer

Amazon CloudWatch Contributor Insights for DynamoDB. Amazon CloudWatch Contributor Insights for DynamoDB is the correct tool because it analyzes DynamoDB request logs to identify the most frequently accessed partition keys, including those causing throttling. It provides top-N keys by request count or throttled events, enabling the database specialist to pinpoint hot partitions responsible for increased latency and throttled requests during peak hours.

Answer

Amazon Inspector

Answer

AWS Config

Answer

AWS CloudTrail logs

Question 6

A database engineer is monitoring an Amazon RDS for PostgreSQL instance and notices that the 'DiskQueueDepth' metric is consistently above 100. The instance uses gp2 storage with 1000 GB allocated. What is the most likely cause of the high disk queue depth?

Accepted Answer

The instance has reached the IOPS limit of the gp2 volume. A consistently high DiskQueueDepth (above 100) on an Amazon RDS for PostgreSQL instance with gp2 storage indicates that the volume is saturating its IOPS limit. gp2 volumes provide a baseline of 3 IOPS per GB (up to 16,000 IOPS), so a 1000 GB gp2 volume has a baseline of 3000 IOPS. When the workload exceeds this baseline, the volume relies on burst credits, and once credits are exhausted, IOPS are throttled to the baseline, causing I/O requests to queue up and the DiskQueueDepth metric to rise.

Answer

Replication lag between the primary and standby instance

Answer

Insufficient memory allocated to the instance

Answer

Network throughput limit is being exceeded

Question 7

A company is migrating its on-premises Oracle database to Amazon RDS for Oracle. The database specialist needs to monitor the migration process and ensure data consistency. Which TWO AWS services should be used together to continuously monitor the replication lag and data integrity?

Accepted Answer

AWS Database Migration Service (AWS DMS). AWS DMS is the correct service because it is specifically designed for database migrations and provides built-in monitoring of replication lag via the 'CDC latency' metric. Amazon CloudWatch is the correct complementary service because it collects and visualizes DMS metrics, including replication lag and task status, and can trigger alarms if data integrity or latency thresholds are breached.

Answer

Amazon RDS Performance Insights

Answer

AWS Schema Conversion Tool (AWS SCT)

Answer

AWS Glue

Question 8

A database specialist is troubleshooting an Amazon DynamoDB table that is experiencing high throttling on write requests. The table has on-demand capacity and uses a composite primary key (partition key and sort key). Which TWO actions should the specialist take to identify and resolve the issue?

Accepted Answer

Examine the partition key value distribution to identify hot partitions. High throttling on write requests often results from uneven partition key distribution, creating hot partitions. Option A is correct: examining the partition key value distribution helps identify hot partitions. Option E is correct: reviewing CloudWatch metrics for WriteThrottleEvents and ConsumedWriteCapacityUnits helps identify throttled write requests and analyze capacity usage. Options B, C, and D are incorrect: DAX is a read cache and does not affect write throughput; changing to provisioned capacity or increasing read capacity units does not resolve write throttling caused by hot partitions.

Answer

Implement DynamoDB Accelerator (DAX) to offload read traffic

Answer

Change the table to provisioned capacity mode

Answer

Increase the read capacity units on the table

Question 9

A database engineer is reviewing Amazon RDS for MySQL error logs and sees repeated authentication failures from the same IP address. The application team confirms the password is correct. What is the most likely cause of these errors?

Accepted Answer

The user 'app_user' does not have access from host '10.0.1.50'. The error logs show authentication failures despite the password being correct, which indicates the issue is not with the password itself but with the host-based access control. In MySQL, user accounts are defined as 'user'@'host', and if the application is connecting from an IP address (e.g., 10.0.1.50) that is not included in the user's allowed hosts, MySQL will reject the connection with an authentication error even if the password is correct. This is a common misconfiguration when migrating or scaling applications across different subnets.

Answer

The password is incorrect

Answer

The 'app_user' account is locked

Answer

The database requires SSL connections

Question 10

A company runs a critical e-commerce application on Amazon Aurora MySQL with a single DB instance. The database has 8 TB of data and uses the default writer endpoint. Recently, the application experienced a 10-minute outage during a primary instance failover. The failover was triggered by an underlying hardware issue. The database specialist needs to minimize downtime during future failovers. The application team is unwilling to modify the application code to handle connection retries. The company has a 99.99% SLA requirement. Which solution should the database specialist implement to meet the SLA with minimal application changes?

Accepted Answer

Create an Amazon RDS Proxy and configure the application to connect to the proxy endpoint. Amazon RDS Proxy sits between the application and the database, pooling and reusing database connections. During a failover, RDS Proxy maintains the client connections and transparently reconnects to the new primary instance, so the application does not experience a connection loss and does not need to implement retry logic. This directly addresses the 10-minute outage by reducing failover downtime to seconds, meeting the 99.99% SLA without application code changes.

Answer

Increase the DB instance class to a larger size to improve performance and reduce failover time

Answer

Enable Multi-AZ deployment with automatic failover

Answer

Create a cross-Region read replica and promote it to primary during failover

Question 11

A database engineer is troubleshooting high CPU usage on an Amazon RDS for PostgreSQL instance. Amazon CloudWatch shows CPU Utilization consistently above 90% during business hours. Which combination of actions should the engineer take to identify the root cause? (Choose TWO.)

Accepted Answer

Review the slow query log to identify long-running queries.. Reviewing the slow query log directly identifies long-running queries that can cause sustained high CPU usage on RDS for PostgreSQL. Option D is correct because Performance Insights provides a visual dashboard of database load and top SQL queries, making it easy to pinpoint which queries are consuming the most CPU resources.

Answer

Enable Enhanced Monitoring and review OS process list.

Answer

Scale up the DB instance to a larger instance class.

Answer

Install pg_stat_statements extension and query it.

Question 12

A company runs a production Amazon DynamoDB table with on-demand capacity. The table stores session data for a web application. Recently, users have reported occasional slow response times. The operations team notices that the table's ConsumedWriteCapacityUnits metric shows occasional spikes that exceed the provisioned throughput (though on-demand auto-scales), and ThrottledWriteEvents metrics show occasional throttling. The application uses the AWS SDK with default retry logic. The database specialist is asked to investigate. Upon reviewing the table configuration, the specialist finds that the table has a simple primary key (partition key only) and the data access pattern is heavily skewed toward a small number of partition keys. The application writes in batches of 25 items using the BatchWriteItem API. What should the specialist recommend to reduce throttling and improve performance?

Accepted Answer

Implement write sharding by adding a random suffix to the partition key to distribute writes more evenly.. The throttling is caused by a hot partition: the table uses a single partition key, and writes are heavily skewed toward a few keys. By adding a random suffix to the partition key (write sharding), the writes are distributed evenly across all partitions, eliminating hot spots and reducing throttling. The on-demand capacity mode already handles overall throughput, but it cannot prevent throttling on individual partitions when access is skewed.

Answer

Increase the provisioned read capacity units to handle the load.

Answer

Switch the table to provisioned capacity mode and increase write capacity.

Answer

Enable DynamoDB Accelerator (DAX) to cache write operations.

Question 13

Arrange the steps to set up cross-Region read replicas for an Amazon Aurora MySQL DB cluster in the correct order.

Accepted Answer

Enable binary logging on the source Aurora MySQL DB cluster, then create a cross-Region read replica in the target Region, then verify replication status.. Cross-Region replicas require binary logging enabled on the source, then creating a read replica in another Region and verifying replication.

Answer

Create a cross-Region read replica in the target Region, then enable binary logging on the source cluster, then verify replication.

Answer

Enable binary logging on the source cluster, then promote the read replica to a standalone cluster, then verify replication.

Answer

Create a read replica in the same Region, then enable cross-Region replication by modifying the source cluster, then verify.

Question 14

Arrange the steps to create an Amazon DynamoDB global table (multi-Region) in the correct order.

Accepted Answer

Create a DynamoDB table, then enable DynamoDB Streams, then add a replica table in another Region, then verify replication.. Global tables require streams enabled, then adding replicas in other Regions for multi-Region replication.

Answer

Create a DynamoDB table, then add a replica table in another Region, then enable DynamoDB Streams, then verify replication.

Answer

Enable DynamoDB Streams, then create a DynamoDB table, then add a replica table in another Region, then verify replication.

Answer

Add a replica table in another Region, then create a DynamoDB table, then enable DynamoDB Streams, then verify replication.

Question 15

Match each AWS database-related CLI command to its function.

Accepted Answer

aws rds describe-db-instances: Retrieves details about RDS DB instances. The correct matches pair each AWS CLI command with its corresponding database service. Common confusions involve swapping commands between RDS, DynamoDB, Redshift, and ElastiCache. Remember that each service has its own command namespace (e.g., 'aws rds', 'aws dynamodb', 'aws redshift', 'aws elasticache').

Answer

aws rds describe-db-instances: Retrieves details about DynamoDB tables

Answer

aws dynamodb describe-table: Retrieves details about Redshift clusters