DBS-C01 Practice Exam 62 — 20 Questions

Question 1

A database specialist is troubleshooting an Amazon Aurora PostgreSQL cluster that is experiencing replication lag on a reader instance. The application performs read-only queries on the reader endpoint. The specialist observes that the AuroraReplicaLag metric is consistently above 1000 milliseconds. The writer instance is not under heavy load. The specialist needs to reduce the replication lag. Which action should the specialist take?

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

Accepted Answer

Check for long-running queries on the reader that are blocking the redo apply process.. Aurora PostgreSQL replication lag on a reader can be caused by long-running queries that block the redo apply process. When a query runs for an extended period, it can prevent the apply process from advancing, leading to increased AuroraReplicaLag. The specialist should identify and terminate such queries to allow the reader to catch up. Other options like resizing or adding readers do not directly address this specific bottleneck.

Answer

Increase the instance size of the reader instance to provide more CPU and memory.

Answer

Modify the reader instance to use a larger instance class with more network bandwidth.

Answer

Enable Aurora Auto Scaling for the reader fleet to add more reader instances.

Question 2

A database specialist is monitoring an Amazon DocumentDB cluster. The application reports slow query performance. The specialist checks the cluster's metrics and sees that 'BufferCacheHitRatio' is below 90% and 'DiskQueueDepth' is high. Which action should the specialist take to improve performance?

Accepted Answer

Increase the instance class to a larger size to provide more memory for the buffer cache.. BufferCacheHitRatio below 90% and high DiskQueueDepth indicate that the instance lacks sufficient memory to cache frequently accessed data. Increasing the instance class provides more RAM, enlarging the buffer cache and reducing disk reads. This directly improves query performance by allowing more data to be served from memory.

Answer

Increase the cluster's storage volume size to improve IOPS.

Answer

Enable Performance Insights to identify the slow queries.

Answer

Add a read replica to distribute the read workload.

Question 3

A database specialist is managing an Amazon DynamoDB table that stores session data. The table has a primary key consisting of a partition key (SessionId) and a sort key (Timestamp). The application frequently queries for the most recent session data for a given SessionId. The specialist wants to optimize the table to reduce the amount of data read during these queries. What should the specialist do?

Accepted Answer

Use the Query operation with the ScanIndexForward parameter set to false and Limit to retrieve only the latest items.. The table's primary key already supports efficient queries by SessionId and Timestamp. By using Query with ScanIndexForward=false and a Limit, the application reads only the most recent items, minimizing read capacity consumption. This is the most direct optimization for the given access pattern.

Answer

Create a global secondary index (GSI) with SessionId as the partition key and Timestamp as the sort key, and project only the needed attributes.

Answer

Enable DynamoDB Accelerator (DAX) to cache the query results.

Answer

Enable DynamoDB Streams to capture changes and process them with AWS Lambda.

Question 4

A database specialist is monitoring an Amazon DynamoDB table that uses on-demand capacity mode. The table has a global secondary index (GSI) with a partition key of 'status' and a sort key of 'timestamp'. The application performs frequent queries on the GSI, and the specialist notices that the GSI's consumed read capacity is much higher than the base table's. CloudWatch metrics show that the GSI has a high number of ThrottledRequests. What is the most likely cause of the throttling on the GSI?

Accepted Answer

The GSI's partition key 'status' has a low cardinality, causing hot partitions and uneven read distribution.. In DynamoDB, a global secondary index with a low-cardinality partition key leads to hot partitions because many items share the same partition key value. Even in on-demand mode, DynamoDB applies per-partition throughput limits, and a single partition cannot exceed those limits. This results in throttling on the GSI despite the table being in on-demand mode. The high consumed read capacity on the GSI relative to the base table indicates that queries are concentrated on a few partitions.

Answer

The GSI's sort key 'timestamp' is causing all reads to target the same partition because timestamps are similar.

Answer

The GSI is using eventual consistency, which requires additional read capacity and causes throttling.

Answer

The GSI's write capacity is not provisioned separately from the base table, causing write throttling that affects reads.

Question 5

A company uses Amazon DynamoDB with a table that has a partition key of CustomerId (string) and a sort key of OrderDate (number). During a flash sale, many requests for a few popular customers cause throttling. The operations team wants to identify which partition keys are consuming the most read capacity units. Which AWS service or feature should they use to analyze the most accessed partition keys?

Accepted Answer

Amazon CloudWatch Contributor Insights for DynamoDB. CloudWatch Contributor Insights for DynamoDB is specifically designed to identify the most accessed and throttled partition keys by analyzing DynamoDB logs. It provides ranked lists and graphs in near real-time, allowing the team to quickly find hot keys during the flash sale. Other options either do not capture read capacity consumption per key or require significant custom effort without the same level of insight.

Answer

DynamoDB Accelerator (DAX) metrics in CloudWatch

Answer

Amazon DynamoDB Streams with an AWS Lambda function to log item-level changes

Answer

AWS CloudTrail data events for the DynamoDB table

Question 6

A database specialist is investigating a production Amazon Aurora PostgreSQL cluster where the application reports intermittent connection timeouts. The specialist suspects the issue is related to the database's connection handling. The cluster uses an Aurora PostgreSQL writer instance (db.r5.xlarge) and a reader instance. The application connects to the writer endpoint. CloudWatch metrics show that DatabaseConnections is consistently near the value of max_connections, and the application logs show errors like 'FATAL: remaining connection slots are reserved for non-replication superuser connections'. What is the most likely cause of the connection timeouts?

Accepted Answer

The Aurora PostgreSQL cluster's max_connections parameter is set too low for the application's connection pool size.. The error 'remaining connection slots are reserved for non-replication superuser connections' is a definitive PostgreSQL message indicating that max_connections has been reached. CloudWatch showing DatabaseConnections near the max_connections value corroborates this. The application's connection pool is likely too large or connections are not being released properly. Increasing max_connections or implementing a connection pooler like RDS Proxy would resolve the issue.

Answer

The security group attached to the Aurora cluster is blocking the application's IP address.

Answer

The Aurora cluster's parameter group has idle_in_transaction_session_timeout set too high, causing connections to remain open.

Answer

The Aurora reader instance is not properly configured for read-only connections, causing write attempts to fail.

Question 7

A database specialist is monitoring an Amazon Aurora PostgreSQL DB cluster. The cluster has a writer instance and a reader instance. The application connects to the reader endpoint for read-only queries. Users report that some read queries return stale data. The specialist needs to ensure that reads are consistent with the latest writes. Which action should the specialist take?

Accepted Answer

Configure the application to use the writer endpoint for all read queries.. Aurora PostgreSQL replicas are asynchronous by default, so reads from the reader endpoint may not include the latest committed writes. To ensure consistency, the application should direct read queries to the writer endpoint. This guarantees that all reads see the most recent data. Other options either increase lag or do not address the consistency requirement. Using the writer for reads is a simple and effective solution when consistency is critical.

Answer

Set the `hot_standby_feedback` parameter to `on` on the writer instance to prevent replication lag.

Answer

Increase the Aurora replica lag by adjusting the `max_standby_streaming_delay` parameter on the reader instance.

Answer

Enable Aurora Auto Scaling for the reader instance to reduce replica lag.

Question 8

A company uses Amazon DynamoDB with a table that has a provisioned capacity mode. The application occasionally receives ProvisionedThroughputExceededException errors, but only for certain items. A database specialist must diagnose the root cause. Which two actions should the specialist take to identify the issue? (Choose two.)

Accepted Answer

Examine the partition key design to determine if a few hot keys are causing uneven distribution of read and write activity.. ProvisionedThroughputExceededException in DynamoDB often stems from either overall capacity being too low or from hot partitions caused by an uneven partition key distribution. Checking CloudWatch consumed capacity metrics reveals if the table is hitting its provisioned limits, while analyzing the partition key design uncovers hot key patterns. Together, these actions diagnose the root cause; merely adding capacity or using unrelated services like Streams or CloudTrail will not identify why specific items are throttled.

Answer

Enable DynamoDB Streams on the table and analyze the stream records for throttled write attempts.

Answer

Use AWS CloudTrail to review the API calls that resulted in ProvisionedThroughputExceededException errors.

Answer

Increase the table's provisioned read and write capacity units immediately to resolve the exceptions.

Question 9

A database specialist is troubleshooting an Amazon Aurora PostgreSQL cluster that is experiencing replication lag on a reader instance. The application performs read-only queries on the reader endpoint. The specialist observes that the AuroraReplicaLag metric is consistently above 1000 milliseconds. The writer instance is not under heavy load. The specialist needs to reduce the replication lag. Which action should the specialist take?

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

Accepted Answer

Configure the application to use a connection pool or persistent connections to reuse existing connections.. A high number of new connections per second indicates connection churn, where clients repeatedly open and close connections. This overhead consumes server resources and increases latency. The most effective solution is to implement connection pooling or persistent connections in the application. This reduces the rate of new connections and improves overall performance. Scaling up or adding replicas does not fix the client behavior.

Answer

Scale up to a larger node type to handle the connection rate.

Answer

Increase the number of replicas to distribute the connection load.

Answer

Enable encryption in transit to reduce connection overhead.

Question 10

A database specialist is managing an Amazon RDS for SQL Server DB instance. Users report that a critical stored procedure that previously ran in seconds now takes minutes to complete. The specialist checks Amazon CloudWatch metrics and sees that the DB instance's CPU utilization is low, but the disk queue depth is high. The specialist needs to identify the cause of the slowdown. Which action should the specialist take to diagnose the issue?

Accepted Answer

Query the sys.dm_os_wait_stats dynamic management view to identify the top wait types.. When CPU is low but disk queue depth is high, the bottleneck is likely disk I/O. The sys.dm_os_wait_stats DMV provides aggregated wait statistics that reveal which resources are causing delays. By identifying the top wait types, such as PAGEIOLATCH or WRITELOG, the specialist can focus on the specific queries or operations causing excessive I/O. This diagnostic step is more direct than enabling Enhanced Monitoring or resizing.

Answer

Review the SQL Server error log for disk-related errors.

Answer

Enable Enhanced Monitoring to view per-process CPU and disk I/O metrics.

Answer

Modify the DB instance class to a larger size with more IOPS.

Question 11

A database specialist manages an Amazon Aurora MySQL DB cluster. Users report that queries against a reader instance intermittently return stale data, even though the application connects to the reader endpoint and the cluster has two Aurora Replicas. The specialist wants to quantify the replication delay and confirm whether the replicas are lagging. Which metric should the specialist monitor in Amazon CloudWatch to directly measure Aurora replica lag?

Accepted Answer

AuroraReplicaLag. The AuroraReplicaLag metric is specifically designed to report replication delay for Aurora Replicas in milliseconds. When applications read from a reader endpoint and observe stale data, the most direct way to confirm replica lag is to monitor this metric per replica. It distinguishes replication delay from other performance issues such as storage throughput or network traffic, enabling targeted remediation.

Answer

NetworkReceiveThroughput

Answer

DiskQueueDepth

Answer

BinLogDiskUsage

Question 12

A database administrator is responsible for an Amazon RDS for SQL Server DB instance. They need to monitor the performance of a specific long-running query that is causing CPU spikes. Which AWS tool provides detailed, query-level performance data with minimal impact on the DB instance?

Accepted Answer

Amazon RDS Performance Insights. Performance Insights is designed to provide query-level performance monitoring for RDS engines, including SQL Server. It captures wait events and top SQL statements by sampling active sessions, which directly identifies the query causing CPU spikes. Other tools like CloudWatch Logs, CloudTrail, or Enhanced Monitoring operate at different layers and cannot attribute CPU usage to specific queries, making Performance Insights the correct choice.

Answer

Enhanced Monitoring for RDS

Answer

Amazon CloudWatch Logs with SQL Server error logs

Answer

AWS CloudTrail with RDS API call logging

Question 13

A database specialist is responsible for an Amazon DynamoDB table that uses on-demand capacity mode. The application experiences sudden spikes in traffic, and the specialist notices that some read requests are being throttled. The specialist wants to monitor the number of read requests that were throttled due to exceeding the table's read capacity. Which CloudWatch metric should be used?

Accepted Answer

ReadThrottleEvents. The ReadThrottleEvents metric specifically counts read requests that DynamoDB throttled due to exceeding the table's read capacity. In on-demand mode, throttling can occur if the request rate exceeds the previous peak by more than double. Monitoring ReadThrottleEvents allows the specialist to detect and respond to throttling, such as by adjusting capacity mode or optimizing queries. This metric is the direct indicator for read throttling.

Answer

ThrottledRequests

Answer

ConsumedReadCapacityUnits

Answer

SuccessfulRequestLatency

Question 14

A company runs an Amazon ElastiCache for Redis cluster in cluster mode disabled. The operations team wants to receive an alert when the cluster's CPU utilization exceeds 80% for 5 minutes. Which AWS service should they use to create this alarm?

Accepted Answer

Amazon CloudWatch. Amazon CloudWatch is the AWS monitoring service that ingests metrics from ElastiCache, including CPUUtilization. It supports creating alarms with thresholds and evaluation periods, such as 80% for 5 minutes, and can trigger notifications via Amazon SNS. The other services serve different purposes: CloudTrail for API auditing, AWS Config for configuration compliance, and EventBridge for event routing. Thus, CloudWatch is the correct service for this alerting requirement.

Answer

Amazon EventBridge

Answer

AWS Config

Answer

AWS CloudTrail

Question 15

A database specialist needs to schedule an automated daily backup of an Amazon RDS for PostgreSQL DB instance and retain the backups for 35 days. The specialist wants the backups to be managed by RDS with no manual intervention. Which action should the specialist take?

Accepted Answer

Configure the DB instance's automated backup retention period to 35 days and set the preferred backup window.. RDS automated backups are the native mechanism for scheduled, retained backups. Configuring the retention period to 35 days causes RDS to keep daily automated backups for that duration and remove older ones automatically. Setting the preferred backup window controls when the daily backup runs, delivering fully managed backups without custom scheduling or cleanup.

Answer

Export the DB instance to Amazon S3 daily using a scheduled task and apply an S3 lifecycle policy for 35-day retention.

Answer

Enable a read replica and take a snapshot of the replica every day using a scheduled event.

Answer

Create a manual DB snapshot on a daily schedule using an AWS Lambda function and set the retention to 35 days.

Question 16

A company runs an Amazon RDS for SQL Server DB instance with Multi-AZ. During a failover test, the application experiences a brief outage, but after the failover, the database specialist notices that the secondary AZ's DB instance is not receiving updates from the primary. The RDS console shows the DB instance status as 'available' and the Multi-AZ status as 'pending'. Which action should the specialist take to resolve this issue?

Accepted Answer

Wait for the Multi-AZ deployment to complete synchronization and monitor the RDS event log for status changes.. The 'pending' Multi-AZ status in Amazon RDS indicates that a change to the Multi-AZ configuration is in progress, such as creating or synchronizing a standby. After a failover, the old primary becomes the new standby, and RDS must synchronize it with the new primary. This process can take time. The specialist should wait for it to complete and monitor the RDS event log for status updates, as no manual intervention is required.

Answer

Reboot the DB instance with a failover to force the secondary to become the primary.

Answer

Restore the DB instance from the latest automated backup to a new Multi-AZ deployment.

Answer

Modify the DB instance to disable Multi-AZ, wait for the change to apply, and then re-enable Multi-AZ.

Question 17

A company uses Amazon DynamoDB with on-demand capacity mode for a new application. During a load test, the application occasionally receives HTTP 400 errors with the code ProvisionedThroughputExceededException, even though the table is in on-demand mode. A database specialist must explain why throttling can still occur and which factor is most likely responsible. What is the most likely cause?

Accepted Answer

The table's partition key is monotonically increasing, causing a hot partition that exceeds the per-partition throughput limit.. On-demand mode automatically scales table capacity, but it still enforces per-partition throughput limits. A monotonically increasing partition key creates a hot partition, and bursts that exceed that partition's ceiling are throttled. This explains why throttling occurs despite on-demand mode and points to partition key design as the root cause.

Answer

The application is using eventually consistent reads instead of strongly consistent reads.

Answer

The table has exceeded the maximum number of items allowed in on-demand mode.

Answer

The table's auto scaling policy is misconfigured and has set the maximum capacity too low.

Question 18

A company runs an Amazon RDS for SQL Server DB instance in a Multi-AZ deployment. The database specialist needs to monitor the health and performance of the database and set up alerts for potential issues. The specialist wants to use Amazon CloudWatch metrics and alarms. Which two CloudWatch metrics should the specialist monitor to detect insufficient memory and excessive disk I/O on the RDS instance? (Choose two.)

Accepted Answer

FreeableMemory. FreeableMemory directly indicates available memory; low values signal memory pressure. DiskQueueDepth measures outstanding disk I/O requests; high values indicate disk bottlenecks. Together, they provide the necessary insight into memory and disk I/O health. Other metrics like CPUUtilization, NetworkReceiveThroughput, and DatabaseConnections are useful but do not specifically address the two issues the specialist wants to detect.

Answer

CPUUtilization

Answer

DatabaseConnections

Answer

NetworkReceiveThroughput

Question 19

A database specialist manages an Amazon Aurora MySQL DB cluster with a single writer and two reader instances. During peak hours, the application experiences intermittent connection timeouts when connecting to the cluster writer endpoint. CloudWatch metrics show that the writer's CPU is at 45%, freeable memory is stable, and there are no long-running queries. The specialist needs to identify the cause of the connection timeouts. Which action should the specialist take to diagnose the issue?

Accepted Answer

Check the Aurora cluster's parameter group for the max_connections setting and compare it to the number of active connections.. Intermittent connection timeouts to an Aurora MySQL writer with low CPU and stable memory frequently point to the max_connections limit being reached. The max_connections parameter in Aurora MySQL is tied to the instance class, and when the number of concurrent connections hits that ceiling, new connection attempts are refused or time out. Checking this parameter against the current connection count is the most direct way to confirm the cause.

Answer

Enable Performance Insights on the writer instance and analyze the database load by wait events.

Answer

Increase the instance size of the writer to a larger class to provide more CPU and memory resources.

Answer

Review the Aurora cluster's error log for messages about aborted connections and restart the writer instance.

Question 20

A database administrator is managing an Amazon RDS for MySQL DB instance. They need to identify the top SQL statements that are consuming the most CPU over the past hour to optimize performance. The DB instance has Performance Insights enabled with a retention period of 7 days. Which action should the administrator take to quickly identify the top SQL statements?

Accepted Answer

Use the Performance Insights dashboard to view the Top SQL tab and sort by DB load.. Performance Insights is designed to help identify performance bottlenecks by providing a Top SQL view that ranks statements by database load, which is a proxy for resource consumption such as CPU. With Performance Insights enabled and a 7-day retention, the administrator can immediately view the top SQL statements over the past hour without additional configuration.

Answer

Query the information_schema.PROCESSLIST table to see currently running queries.

Answer

Enable the slow query log and use the mysql.slow_log table to find queries with high execution time.

Answer

Use Amazon CloudWatch Logs Insights to analyze the error log for CPU-related messages.