DBS-C01 Monitoring and Troubleshooting Practice Test 6 — 15 Questions

Question 1

A company is using Amazon RDS for MySQL with Multi-AZ deployment. The application team reports intermittent connection timeouts. CloudWatch shows increased DatabaseConnections and CPU Utilization during peak hours. Which action should the database specialist take to troubleshoot the issue?

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

Accepted Answer

Enable slow query log and analyze queries.. Enabling the slow query log allows the database specialist to identify long-running or inefficient queries that contribute to high CPU utilization and increased database connections, leading to connection timeouts during peak hours. Option A is incorrect because Enhanced Monitoring provides additional metrics (e.g., OS-level metrics) but does not directly address the root cause of the timeouts; it is useful for deeper analysis but not the primary troubleshooting action. Option C is incorrect because creating a read replica and redirecting read traffic reduces load on the primary for read operations, but the issue likely involves write-intensive or poorly optimized queries affecting the primary; while it might alleviate some load, it is not a direct troubleshooting step to identify the cause. Option D is incorrect because failing over to the standby instance is for high availability and disaster recovery, not for resolving performance issues; it would restart the database but not fix the underlying queries or resource contention.

Answer

Add enhanced monitoring to collect additional metrics.

Answer

Create a read replica and redirect read traffic.

Answer

Failover to the standby instance to refresh connections.

Question 2

A financial services company runs a critical application on Amazon DynamoDB. Recently, they observed increased latency and throttled requests. Upon reviewing CloudWatch metrics, they see that WriteCapacityUnits consumed is consistently below the provisioned capacity, but ReadCapacityUnits consumed is frequently at 100%. The application performs equal mix of strongly consistent reads and writes. What is the most likely cause of the throttling?

Accepted Answer

Hot partitions causing uneven read traffic distribution.. Throttling on reads with provisioned capacity still available indicates hot partitions. Option B is wrong because adaptive capacity helps but does not eliminate hot partitions. Option C is wrong because writes are not throttled. Option D is wrong because strongly consistent reads consume twice the read capacity units, but the issue is hot partitions.

Answer

Adaptive capacity is automatically adjusting partition throughput.

Answer

Write capacity is insufficient for the workload.

Answer

Strongly consistent reads are consuming twice the RCU.

Question 3

A company uses Amazon Aurora MySQL. They notice that the DB cluster's failover took longer than expected during a recent primary instance failure. CloudWatch shows Failover latency of 120 seconds. Which configuration change would most likely reduce the failover time?

Accepted Answer

Configure the application to use the cluster endpoint with Aurora JDBC driver's fast failover feature.. Configuring the application to use the cluster endpoint with the Aurora JDBC driver's fast failover feature allows the driver to quickly detect the new writer after a failover and reconnect, significantly reducing the perceived failover time by avoiding DNS propagation delays. Option A is incorrect because increasing the instance class improves performance but does not affect failover speed. Option B is incorrect because backup retention period is unrelated to failover latency. Option C is incorrect because Aurora MySQL is already Multi-AZ by design; enabling Multi-AZ is not a separate configuration step.

Answer

Increase the instance class of the primary and replica instances.

Answer

Increase the backup retention period to 35 days.

Answer

Enable Multi-AZ on the DB cluster.

Question 4

A company is using Amazon DynamoDB with provisioned capacity. They notice an increase in throttled write requests. The workload consists of writes to a single partition key. Which TWO actions would help reduce throttling?

Accepted Answer

Increase the provisioned write capacity units.. Option B is correct because throttling on a provisioned-capacity table occurs when write requests exceed the table's allocated Write Capacity Units (WCUs); raising the provisioned WCU value directly increases the write throughput budget available to absorb the higher request rate. Option C is correct because DynamoDB auto scaling adjusts provisioned WCUs automatically in response to consumed capacity, and adaptive capacity (now automatic in DynamoDB) isolates and boosts frequently accessed partitions, helping the table keep pace with the increased write load without manual tuning. Option A is not correct because adding a GSI with a different partition key does not relieve write throttling on the base table—it actually consumes additional WCUs to maintain the index. Option D is not correct because DAX only caches reads (eventually consistent GetItem, Query, and Scan operations) and does not accelerate or cache writes. Option E is not correct because the workload writes to a single partition key, so write sharding would require changing the application's key schema and access pattern, which is not a valid remedy as stated for the existing single-key workload.

Answer

Add a global secondary index with a different partition key.

Answer

Use DynamoDB Accelerator (DAX) for write caching.

Answer

Implement write sharding by adding a suffix to the partition key.

Question 5

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.. Option A is correct because MemoryPressure and LogFileSyncDuration are Oracle-specific CloudWatch metrics for RDS that directly indicate whether the low FreeableMemory is causing memory pressure and whether commit/redo write latency (LogFileSync) is being affected by the I/O and memory contention. Option B is correct because V$MEMORY_TARGET_ADVICE is Oracle's memory advisor view that shows how estimated DB time would change at different MEMORY_TARGET sizes, which is exactly the diagnostic needed to determine whether the instance is undersized for its current workload. Option E is correct because V$SGASTAT and V$PGASTAT break down current SGA and PGA allocation, letting the specialist see which memory components (buffer cache, shared pool, PGA work areas) are consuming memory and contributing to the low FreeableMemory. Option C is not appropriate because storage auto scaling only grows EBS storage capacity and does not address memory exhaustion. Option D is not appropriate as a diagnostic step because resizing the DB instance class is a remediation action, not a way to diagnose the root cause of the memory pressure.

Answer

Enable storage auto scaling to increase allocated storage.

Answer

Increase the DB instance class to allocate more memory.

Question 6

Refer to the exhibit. An IAM policy attached to an IAM role used by an AWS Lambda function. The Lambda function is invoked by Amazon API Gateway and reads from a DynamoDB table. The function is experiencing permission errors when calling DynamoDB GetItem. What is the most likely cause?

Accepted Answer

The policy does not grant access to DynamoDB indexes if the function uses a query on a Global Secondary Index.. The correct answer is B: the policy does not grant access to DynamoDB indexes if the function uses a query on a Global Secondary Index. In DynamoDB, when a request targets a Global Secondary Index (GSI) or Local Secondary Index (LSI), the IAM policy must include the index ARN (table-name/index/index-name) in the Resource element; a policy that only lists the base table ARN will deny the operation with an AccessDeniedException even though the base table is permitted. Since the exhibit shows a policy scoped to the table but not its indexes, the GetItem/Query against the index fails. Option A is unlikely because the function is already being invoked and reaching DynamoDB, indicating the role was assumed successfully. Option C is incorrect because the scenario specifically involves index access, not a missing base-table GetItem permission. Option D is incorrect because the Lambda ARN is not used in a DynamoDB resource field; DynamoDB resources are table and index ARNs.

Answer

The IAM role trust policy does not allow Lambda to assume the role.

Answer

The dynamodb:GetItem action is not listed in the policy.

Answer

The Lambda function ARN in the resource field is incorrect.

Question 7

A social media company runs a multi-region application on Amazon DynamoDB with global tables. The application is deployed in us-east-1 and eu-west-1. Recently, they enabled DynamoDB Streams on the table to trigger an AWS Lambda function for real-time analytics. The Lambda function runs in us-east-1. After enabling streams, they notice that the Lambda function is triggered multiple times for the same update, and the application's write latency in eu-west-1 has increased. The company has strict latency requirements. A database specialist is asked to resolve the issue. What should the database specialist recommend?

Accepted Answer

Modify the Lambda function to check the 'awsRegion' attribute in the stream record and ignore records from other regions.. With DynamoDB global tables, Streams on a replica include records replicated from other regions, so a Lambda in us-east-1 will see updates originating in eu-west-1 and reprocess them, causing duplicate triggers. Filtering on the awsRegion attribute in the stream record lets the Lambda ignore records that did not originate in us-east-1, eliminating redundant processing. This also reduces cross-region read amplification that can contribute to latency.

Answer

Increase the Lambda function's reserved concurrency to handle duplicate events faster.

Answer

Create a separate Lambda function in eu-west-1 and use a local stream.

Answer

Disable DynamoDB Streams on the eu-west-1 replica table.

Question 8

A company runs a document management system using Amazon S3 and Amazon DynamoDB. The application writes document metadata to DynamoDB and stores the document in S3. Recently, users report that occasionally documents are saved in S3 but the corresponding metadata is missing in DynamoDB. The application writes to DynamoDB first, then to S3. If the S3 upload fails, the application retries. The database specialist suspects a transaction consistency issue. The application is running on multiple EC2 instances behind an Application Load Balancer. What should the specialist recommend to ensure that both the metadata and document are stored consistently?

Accepted Answer

Use DynamoDB transactions to write metadata and initiate S3 upload within the same transaction.. Using DynamoDB transactions ensures atomicity; if the S3 upload fails, the transaction can be rolled back. Option B is wrong because DynamoDB Streams with Lambda introduces eventual consistency and possible duplicates. Option C is wrong because writing to S3 first still leaves inconsistency if DynamoDB fails. Option D is wrong because idempotency tokens help with duplicates but not atomicity.

Answer

Use DynamoDB Streams to trigger an AWS Lambda function that performs the S3 upload.

Answer

Reverse the order: upload to S3 first, then write to DynamoDB.

Answer

Implement an idempotency key in the application to retry the entire operation.

Question 9

A company uses Amazon DynamoDB as a session store for a web application. The application uses a TTL attribute to expire old sessions. The company noticed that expired sessions are not being deleted promptly, causing the table size to grow and increasing costs. The TTL attribute is defined as 'expire_time' with a Unix epoch timestamp. The database specialist verified that TTL is enabled. What should the specialist do to ensure expired sessions are deleted in a timely manner?

Accepted Answer

Increase the provisioned write capacity on the table to allow TTL to delete items faster.. TTL deletion can be delayed if the table has a high write rate; increasing provisioned write capacity can allocate more resources to the background deletion process, allowing expired items to be removed more quickly. Option A is wrong because changing the attribute type to String would not resolve the deletion delay (the TTL attribute should be a Number). Option C is wrong because there is no 'ttl_deletion_lag' parameter in DynamoDB. Option D is wrong because using a Lambda function to scan and delete expired items is unnecessary and inefficient compared to properly tuning TTL.

Answer

Change the TTL attribute type to String format.

Answer

Configure the 'ttl_deletion_lag' parameter to a lower value.

Answer

Create an AWS Lambda function that scans the table and deletes expired items.

Question 10

A company is running a production Amazon Aurora MySQL-Compatible Edition database. The database has recently experienced several failovers due to replica lag. The DBA needs to implement monitoring to detect replica lag early. Which THREE metrics should be monitored to assess replication health? (Select THREE.)

Accepted Answer

DatabaseConnections. Option C (ReplicaLag) is correct because it is the CloudWatch metric that reports the time difference in seconds between the latest write on the primary and the corresponding write applied on an Aurora replica, directly exposing replication delay. Option E (AuroraReplicaLag) is correct because it is the Aurora-specific metric measuring the lag in milliseconds between a replica and its writer instance, which is the primary signal for detecting replica lag early. Option A (DatabaseConnections) is correct because monitoring the number of connections to each Aurora instance helps reveal uneven read traffic distribution or a replica being overwhelmed, which can contribute to lag and failover risk. Option B (ActiveTransactions) is not a standard Aurora replication-health metric for detecting replica lag, and Option D (BufferCacheHitRatio) reflects buffer pool efficiency rather than replication delay, so neither belongs in this monitoring set.

Answer

ActiveTransactions

Answer

BufferCacheHitRatio

Question 11

A company uses Amazon DynamoDB for a highly transactional application. The application is experiencing increased latency and throttled requests. The operations team notices that the DynamoDB table's read and write capacity utilization is consistently near 100%. The table uses on-demand capacity mode. What is the MOST likely cause of the throttling?

Accepted Answer

The table has reached the per-table throughput limit for on-demand mode.. In on-demand capacity mode, DynamoDB automatically scales to accommodate workload, but there are per-table throughput limits (e.g., 40,000 RCU and 40,000 WCU for on-demand tables in many regions). If the table consistently hits 100% utilization and is throttled, it is likely that the table has reached these per-table limits. The most likely cause is that the table has reached the per-table throughput limit for on-demand mode.

Answer

The table is configured as a global table and cross-region replication is causing write conflicts.

Answer

The application is not using DynamoDB Accelerator (DAX) to cache reads.

Answer

The table's partition key design is causing hot partitions, and adaptive capacity is not enabled.

Question 12

A company is running a self-managed MongoDB cluster on Amazon EC2. The cluster consists of three replica set members in different Availability Zones. The primary node recently experienced a crash, and the cluster failed over to a secondary. However, the new primary is showing significantly higher latency. The operations team wants to ensure that failover is fast and consistent. What should be done to improve the failover reliability?

Accepted Answer

Use Amazon EBS io2 Block Express volumes with provisioned IOPS.. Amazon EBS io2 Block Express volumes provide high IOPS and low latency, which can significantly reduce the time required for a secondary node to catch up and become the new primary after a failover. This improves failover reliability and reduces latency spikes. Option B is incorrect: EBS Multi-Attach is designed for shared block storage across multiple instances and is not suitable for MongoDB replica sets; using it could lead to data corruption. Option C is incorrect: while instance store volumes offer high I/O performance, they are ephemeral; if the instance fails, data is lost, making them unreliable for database workloads. Option D is incorrect: EBS snapshots are for backup and disaster recovery, not for improving failover performance.

Answer

Use Amazon EBS Multi-Attach to allow all replicas to share the same volume.

Answer

Switch to instance store volumes for better I/O performance.

Answer

Configure EBS snapshots to be taken every 5 minutes.

Question 13

Refer to the exhibit. A DBA is troubleshooting a performance issue on an RDS for MySQL DB instance. The DBA runs the AWS CLI command shown. Based on the output, which of the following is a potential performance bottleneck?

Accepted Answer

The storage type is gp2, which may have limited IOPS performance.. The instance uses gp2 storage, which has burstable IOPS. If the burst balance is depleted, performance can degrade. The engine version is recent, Multi-AZ is not enabled, but that affects availability, not necessarily performance. DB instance status is available so no issue there.

Answer

The DB instance is not Multi-AZ, causing failover delay.

Answer

The DB instance status is 'available', meaning it is not accepting connections.

Answer

The engine version 8.0.27 has a known performance bug.

Question 14

A company runs a critical application on Amazon RDS for PostgreSQL with a Multi-AZ deployment. The application experiences intermittent connection timeouts and slow query performance. The CloudWatch metrics show that the 'ReadLatency' and 'WriteLatency' metrics are elevated during peak hours. The 'CPUUtilization' is consistently below 30%, and 'DatabaseConnections' is within limits. The 'BurstBalance' for the gp2 storage is frequently dropping to 0%. The DB instance is a db.r5.large with 300 GB of gp2 storage. The company wants to resolve the latency issues without significant cost increase. Which solution should the company implement?

Accepted Answer

Increase the allocated storage to 600 GB to increase baseline IOPS.. The gp2 storage BurstBalance dropping to 0% indicates that the volume has exhausted its burst credits and is now limited to baseline IOPS. For a 300 GB gp2 volume, baseline IOPS is 3 IOPS/GB * 300 = 900 IOPS, which is insufficient during peak hours. Increasing storage to 600 GB raises baseline IOPS to 1800, providing more sustained performance without the cost of io1.

Answer

Add a read replica to offload read traffic.

Answer

Enable Performance Insights to identify the root cause.

Answer

Switch the storage type to io1 with 3000 provisioned IOPS.

Question 15

A company's Amazon RDS for PostgreSQL instance is running out of storage. The DB instance has auto-scaling enabled, but the storage did not increase. What is the most likely cause?

Accepted Answer

The DB instance has exceeded the Maximum Storage Duration setting.. Amazon RDS storage auto-scaling has a Maximum Storage Threshold setting that defines the upper limit to which storage can automatically scale. If the DB instance has reached this maximum threshold, auto-scaling will not increase storage further, even if the instance is running out of space. The most likely cause is that the instance has exceeded the Maximum Storage Threshold (not "Maximum Storage Duration" as stated in the option, but the intended answer).

Answer

The DB instance class does not support storage auto-scaling.

Answer

The DB instance is smaller than the minimum storage size for auto-scaling.

Answer

The storage usage has not reached the maximum allocated storage.