DBS-C01 Monitoring and Troubleshooting Practice Test 16 — 15 Questions

Question 1

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?

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

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 2

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 3

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 4

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 5

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 6

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. Option A is correct because with a composite primary key, throttling on writes often stems from an uneven partition key value distribution that creates hot partitions; examining the key distribution lets the specialist detect and redesign the key to spread writes evenly. Option E is correct because CloudWatch publishes DynamoDB metrics such as WriteThrottleEvents and ConsumedWriteCapacityUnits, which directly reveal write throttling and capacity consumption patterns needed to diagnose the issue. Option B is not correct because DAX is an in-memory cache that offloads read traffic, not write throttling, so it does not address the problem. Option C is not correct because switching to provisioned capacity mode does not by itself resolve throttling and can worsen it if capacity is under-provisioned. Option D is not correct because increasing read capacity units affects reads, not the write throttling being experienced.

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 7

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 8

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 9

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 10

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 11

A company uses Amazon ElastiCache for Redis as a caching layer for a web application. They observe a sudden increase in CPU utilization on the cache cluster, and the application experiences higher latency. Which action should be taken to diagnose the issue?

Accepted Answer

Monitor Amazon CloudWatch metrics for the ElastiCache cluster to identify the cause.. Amazon CloudWatch provides native metrics for ElastiCache (CPUUtilization, EngineCPUUtilization, CurrConnections, CacheHits/Misses, Evictions, etc.) that allow you to pinpoint the cause of increased CPU and latency, such as a spike in connections, heavy commands, or evictions. Monitoring these metrics is the correct first diagnostic step before making changes.

Answer

Enable query profiling on the ElastiCache cluster.

Answer

Disable persistence to reduce CPU overhead.

Answer

Immediately scale up to a larger node type.

Question 12

A company runs an Amazon Aurora MySQL database cluster with one writer and two readers. The application suddenly fails with 'Too many connections' error. The writer instance's maximum connections is set to 1000. Which configuration change would best resolve the issue while maintaining high availability?

Accepted Answer

Enable Amazon RDS Proxy for the database cluster.. Amazon RDS Proxy pools and shares database connections, allowing many application connections to reuse a smaller set of actual database connections. This resolves 'Too many connections' without over-provisioning max_connections, and it maintains high availability by automatically routing to a healthy instance during failover.

Answer

Increase the max_connections parameter on the writer instance to 5000.

Answer

Redirect all write requests to one of the read replicas.

Answer

Manually kill idle connections from the database.

Question 13

A company uses Amazon DynamoDB with global tables. They notice that changes made in one region are not appearing in another region after several minutes. Which CloudWatch metric should be monitored to check the replication lag?

Accepted Answer

ReplicationLatency. ReplicationLatency measures the time between the last update on the source table and the last update on the replica table. Option A (ConsumedWriteCapacityUnits) is wrong because it measures write capacity usage, not replication lag. Option B (SuccessfulRequestLatency) is wrong because it measures request latency, not replication lag. Option D (ThrottledRequests) is wrong because it indicates throttling, not replication lag.

Answer

ConsumedWriteCapacityUnits

Answer

SuccessfulRequestLatency

Answer

ThrottledRequests

Question 14

A team is troubleshooting an Amazon RDS for SQL Server instance that is running out of storage. The instance uses General Purpose SSD (gp2) storage. The team wants to increase storage without downtime. Which action should they take?

Accepted Answer

Modify the DB instance to increase allocated storage.. Amazon RDS supports increasing allocated storage for a DB instance with no downtime by modifying the DB instance's allocated storage setting. This operation is an online change that does not require a reboot and can be applied immediately, allowing the instance to grow its storage volume while remaining available. This is the standard, least-disruptive way to resolve a storage-full condition on RDS.

Answer

Migrate to gp3 storage.

Answer

Add a read replica to offload queries.

Answer

Take a snapshot and restore to a larger instance.

Question 15

A developer is using AWS Database Migration Service (DMS) to migrate a database from on-premises to Amazon RDS. The migration task is failing with 'Insufficient memory' error. Which resource should be increased to resolve this?

Accepted Answer

Increase the size of the DMS replication instance.. AWS DMS runs the migration task on a dedicated replication instance, and the 'Insufficient memory' error indicates that the replication instance's memory is exhausted while buffering change data capture (CDC) or full-load rows. Increasing the replication instance class (more RAM) directly resolves this. The source, target, and S3 staging resources are not where DMS allocates its task memory.

Answer

Increase the memory on the source database.

Answer

Increase the Amazon S3 bucket size for staging.

Answer

Increase the memory on the target RDS instance.