DBS-C01 Practice Exam 66 — 20 Questions

Question 1

A startup is using Amazon ElastiCache for Redis to cache session data. They deployed a single Redis node (cache.t3.micro) in us-west-2. The application reports high latency when reading session data. CloudWatch metrics show CPUUtilization at 90% and Evictions at 100 per minute. The cache hit ratio is 80%. The database specialist suspects the node is overloaded. What should the specialist do to improve performance?

Accepted Answer

Scale up to a larger node type, such as cache.m5.large.. Option D is correct because increasing the node size provides more CPU and memory, reducing evictions and latency. Option A is wrong because a read replica helps with read scaling but the node is a primary. Option B is wrong because Redis Cluster mode requires multiple shards and may add complexity. Option C is wrong because reducing TTL might increase cache misses.

Answer

Add a read replica to offload read traffic.

Answer

Enable cluster mode and add more shards.

Answer

Decrease the TTL for session keys to reduce memory usage.

Question 2

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.. Option B is correct. The policy grants GetItem and Query on the table ARN, but it does not include the 'dynamodb:GetItem' action? Wait, it does include it. Actually, the correct answer is that the policy is missing the 'dynamodb:GetItem' action? No, it's there. The issue is that the function is using a conditional write? Hmm. Let's analyze: The policy allows GetItem and Query on the table. That should work. But perhaps the function is trying to access a specific index? The policy does not include access to indexes. Option B says missing index ARN. That is plausible. Option A is wrong because the Lambda resource is fine. Option C is wrong because GetItem is included. Option D is wrong because the role trust policy is not shown.

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 3

A retail company uses Amazon RDS for PostgreSQL as the backend for its e-commerce platform. During a flash sale, the database experienced high CPU utilization and increased the number of active connections. The application team reported that some queries timed out. The database specialist reviewed the slow query log and found that several queries were performing sequential scans on large tables due to missing indexes. The specialist created the necessary indexes, but the issue persists for some queries. Upon further investigation, the specialist notices that the query planner is still choosing sequential scans for some queries. What should the database specialist do to ensure the query planner uses the indexes?

Accepted Answer

Run the ANALYZE command to update table statistics.. Option A is correct because running ANALYZE updates table statistics, which helps the query planner choose the best plan. Option B is wrong because increasing maintenance_work_mem helps with autovacuum but not query planning. Option C is wrong because disabling sequential scans is a brute-force approach that may not be optimal. Option D is wrong because setting cpu_tuple_cost changes the cost model but might not be necessary.

Answer

Increase maintenance_work_mem to speed up index creation.

Answer

Decrease the random_page_cost to make indexes more attractive.

Answer

Set enable_seqscan to off to force index usage.

Question 4

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.. Option B is correct because using DynamoDB transactions ensures atomicity; if the S3 upload fails, the transaction can be rolled back. Option A 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 5

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.. Option D: On-demand mode has a per-table throughput limit (e.g., 40,000 read/write units per second). When sustained traffic exceeds that, requests are throttled. Option A: Global tables replicate writes to other regions but do not cause throttling. Option B: DynamoDB Accelerator (DAX) reduces latency but can still see throttling if the table itself is throttled. Option C: Adaptive capacity automatically scales partitions but cannot exceed the on-demand limit.

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 6

A database specialist is troubleshooting a slow Amazon RDS for PostgreSQL query. The specialist has enabled Performance Insights and sees that the database load is high. Which additional tool can provide detailed information about the specific queries causing the load?

Accepted Answer

Use Enhanced Monitoring to view OS-level metrics and correlate with performance insights.. Option B is correct because Enhanced Monitoring provides OS-level metrics, while Performance Insights provides query-level details. Option A is wrong because CloudWatch Logs is for log files. Option C is wrong because AWS CloudTrail is for API calls. Option D is wrong because VPC Flow Logs capture network traffic.

Answer

Use VPC Flow Logs to analyze network traffic to the database.

Answer

Use Amazon CloudWatch Logs to analyze the PostgreSQL error logs.

Answer

Use AWS CloudTrail to view database API calls.

Question 7

A company uses Amazon DocumentDB (with MongoDB compatibility) for its application. The application is experiencing high write latency. The DB cluster has one primary instance and two replicas. Which action should be taken to identify the cause?

Accepted Answer

Enable Enhanced Monitoring and review OS-level metrics like CPU, memory, and I/O.. Option B is correct because enabling Enhanced Monitoring at the instance level provides OS-level metrics that can help identify resource bottlenecks causing high write latency. Option A is wrong because profiling queries in the slow query log may show slow queries but not necessarily latency at the OS level. Option C is wrong because creating additional replicas does not reduce write latency on the primary. Option D is wrong because switching to Amazon DynamoDB is a major architectural change, not a troubleshooting step.

Answer

Migrate the database to Amazon DynamoDB for better write performance.

Answer

Add more read replicas to distribute the load.

Answer

Enable slow query logging and analyze slow queries.

Question 8

A developer needs to monitor the number of throttled read requests for a DynamoDB table. Which CloudWatch metric should be used?

Accepted Answer

ReadThrottleEvents. Option C is correct because ReadThrottleEvents counts throttled read requests. Option A is wrong because ConsumedReadCapacityUnits shows successful reads, not throttled ones. Option B is wrong because ThrottledWriteEvents counts write throttles. Option D is wrong because SuccessfulRequestLatency measures latency, not throttles.

Answer

ThrottledWriteEvents

Answer

SuccessfulRequestLatency

Answer

ConsumedReadCapacityUnits

Question 9

Which TWO actions should be taken to troubleshoot high memory usage on an Amazon ElastiCache for Redis node? (Choose two.)

Accepted Answer

Monitor the Evictions CloudWatch metric.. Options A and D are correct. Checking the evictions metric (Evictions) shows if memory is being freed due to maxmemory policy. Increasing the maxmemory parameter can alleviate memory pressure. Option B (enabling Reserved Memory) reserves memory for overhead, not a troubleshooting step. Option C (monitoring CPUUtilization) is for CPU, not memory. Option E (enabling cluster mode) is a configuration change, not a troubleshooting step.

Answer

Monitor CPUUtilization CloudWatch metric.

Answer

Enable cluster mode to distribute memory across shards.

Answer

Enable Reserved Memory parameter group setting.

Question 10

A company has an Amazon DynamoDB table with on-demand capacity. Users report that write requests are occasionally throttled during peak hours. The application uses the AWS SDK and retries with exponential backoff. Which monitoring approach should be used to identify the cause of throttling?

Accepted Answer

Monitor CloudWatch metrics for ThrottledRequests and ConsumedWriteCapacityUnits.. Option C is correct because CloudWatch metrics such as WriteThrottleEvents, ConsumedWriteCapacityUnits, and ProvisionedWriteCapacityUnits (for on-demand, the provisioned is the maximum) help identify throttling causes. Option A is wrong because DynamoDB Streams track changes, not throttling. Option B is wrong because CloudTrail logs API calls but not throttling events at the item level. Option D is wrong because VPC Flow Logs capture network traffic, not database throttling.

Answer

Use AWS CloudTrail to monitor PutItem API calls for throttling errors.

Answer

Analyze VPC Flow Logs to check for network congestion.

Answer

Enable DynamoDB Streams and process records to monitor throttled requests.

Question 11

A company is running Amazon RDS for MySQL and notices that the database CPU utilization is consistently above 80% during peak hours. The application performance is degrading. Which action should be taken first to troubleshoot the issue?

Accepted Answer

Enable Performance Insights to identify the queries causing high CPU usage.. Option B is correct because enabling Performance Insights provides a detailed analysis of database performance, helping to identify the root cause of high CPU utilization. Option A is wrong because increasing instance size without understanding the cause may lead to unnecessary costs. Option C is wrong because creating a read replica does not directly address CPU utilization on the primary instance. Option D is wrong because switching to a different database engine is a major change and not a troubleshooting step.

Answer

Increase the instance size of the RDS instance immediately.

Answer

Create a read replica to offload read traffic.

Answer

Switch the database engine to Amazon Aurora for better performance.

Question 12

Which THREE metrics should be monitored to troubleshoot a slow Amazon Redshift query? (Choose three.)

Accepted Answer

DiskSpaceUsage. Options B, C, and D are correct. WLMQueueWaitTime measures time queries wait in queue, QueryDuration measures execution time, and DiskSpaceUsage indicates if disk spills are causing slowness. Option A (NetworkThroughput) is about network, not query performance. Option E (DatabaseConnections) is about connection count, not query speed.

Answer

DatabaseConnections

Answer

NetworkThroughput

Question 13

A company runs a critical application on Amazon RDS for PostgreSQL. The application team reports that the database occasionally becomes unresponsive for a few seconds. CloudWatch metrics show 'CPUSurplusCreditsCharged' and 'CPUSurplusCredits' are not 0. The instance is a db.t3.medium. What is the likely cause and how should it be fixed?

Accepted Answer

The instance is out of CPU credits and is being throttled; switch to a larger or non-burstable instance. Option A is correct because t3 instances are burstable and use CPU credits. When credits are exhausted, they can use surplus credits, which incur charges. If the workload is consistently high, the instance may run out of credits and become throttled, causing unresponsiveness. The fix is to switch to a T3 unlimited mode (but that incurs charges) or use a non-burstable instance (e.g., m5). Option B is wrong because modifying Multi-AZ does not affect CPU credits. Option C is wrong because enabling Enhanced Monitoring does not fix credit exhaustion. Option D is wrong because storage optimization does not affect CPU credits.

Answer

Enable Enhanced Monitoring to diagnose the issue

Answer

Increase the allocated storage to improve I/O

Answer

The instance is experiencing a failover; enable Multi-AZ

Question 14

A company is using Amazon Redshift for data warehousing. The data engineering team notices that queries are running slower than expected. CloudWatch shows that 'CPUUtilization' is high and 'DiskSpaceUsage' is also high. The cluster has 4 dc2.large nodes. What is the most likely cause of the performance degradation?

Accepted Answer

Queries are spilling to disk due to insufficient memory. Option B is correct because high disk usage on dc2 nodes indicates that the cluster is spilling to disk due to insufficient memory. Option A is wrong because network throughput is not indicated. Option C is wrong because WLM queue waits would show in other metrics. Option D is wrong because high CPU alone does not explain disk usage.

Answer

Insufficient network bandwidth between nodes

Answer

CPU is the bottleneck and needs more compute nodes

Answer

Workload management (WLM) queue is causing query waits

Question 15

A company notices that its Amazon DynamoDB table is consuming more read capacity than expected. The table has a global secondary index (GSI) with a different sort key. Which action would most likely reduce the read consumption?

Accepted Answer

Enable DAX (DynamoDB Accelerator) to cache read results.. Queries that use the GSI can consume read capacity from the index. However, if the query uses the base table's primary key, it consumes from the base table. Option A is wrong because local secondary indexes don't help. Option B is wrong because adjusting write capacity doesn't affect reads. Option C is correct because enabling DynamoDB Accelerator (DAX) caches reads, reducing read capacity consumption. Option D is wrong because changing the sort key is not a direct solution.

Answer

Increase the write capacity of the table.

Answer

Change the sort key of the base table to match the GSI sort key.

Answer

Create a local secondary index (LSI) with the same sort key as the GSI.

Question 16

Which TWO metrics should be monitored together to detect a memory leak in an Amazon RDS for Oracle DB instance? (Choose TWO.)

Accepted Answer

FreeableMemory. Options A and D are correct because FreeableMemory shows available memory, and SwapUsage indicates swapping, which occurs when memory is exhausted. Option B (NetworkThroughput) is not memory-related. Option C (ReadIOPS) is I/O-related. Option E (DatabaseConnections) is connection-related.

Answer

ReadIOPS

Answer

DatabaseConnections

Answer

NetworkThroughput

Question 17

A company is using Amazon DynamoDB with auto scaling. The application is experiencing increased read latency. The monitoring shows that the ReadThrottleEvents metric is high. Which action should the company take to reduce read throttling?

Accepted Answer

Implement DynamoDB Accelerator (DAX) for caching.. Option C is correct because DynamoDB Accelerator (DAX) reduces read latency and throttling by caching. Option A is wrong because increasing write capacity doesn't help reads. Option B is wrong because enabling Streams may add overhead. Option D is wrong because switching to on-demand may increase cost but not necessarily fix throttling if workload is bursty.

Answer

Switch the table to on-demand capacity mode.

Answer

Enable DynamoDB Streams on the table.

Answer

Increase the write capacity units.

Question 18

A company has an Amazon RDS for PostgreSQL database that is experiencing intermittent connection timeouts. The application logs show 'FATAL: remaining connection slots are reserved for non-replication superuser connections'. The database has a max_connections parameter set to 200. The application uses a connection pool. The DBA checks the CloudWatch metric 'DatabaseConnections' and sees it at 195 during peak hours. The application is deployed on AWS Lambda with a provisioned concurrency of 100. The Lambda function creates a new connection for each invocation. What should the DBA do to resolve the issue?

Accepted Answer

Set up Amazon RDS Proxy to manage the database connections from Lambda.. Option A is correct because the Lambda function creates new connections, exhausting the pool. Using RDS Proxy manages connections efficiently. Option B is wrong because increasing max_connections may cause resource contention. Option C is wrong because reducing provisioned concurrency may not solve the root cause. Option D is wrong because decreasing max_connections would worsen the issue.

Answer

Reduce the Lambda provisioned concurrency to 50.

Answer

Increase max_connections to 500 to accommodate more connections.

Answer

Decrease max_connections to 100 to reserve more slots.

Question 19

A company's Amazon Redshift cluster is experiencing slow query performance. The cluster has three nodes. The administrator wants to identify if the issue is due to data distribution skew. Which approach should be used?

Accepted Answer

Query the STV_SLICES table to compare disk usage across slices.. Option A is correct because checking the STV_SLICES table shows disk usage per slice, revealing data distribution skew. Option B is wrong because the STL_QUERY table logs query text, not distribution. Option C is wrong because the STV_WLM_SERVICE_STATE table shows queue state, not distribution. Option D is wrong because CloudWatch metrics like CPUUtilization do not indicate distribution skew.

Answer

Examine the STL_QUERY table to analyze query execution times.

Answer

Check the STV_WLM_SERVICE_STATE table to see current queue state.

Answer

Review CloudWatch metrics for CPUUtilization per node.

Question 20

A company uses Amazon Redshift for data warehousing. They run a daily ETL job that loads data into the cluster. Recently, the job started failing with 'Disk Full' errors. The cluster has 5 RA3 nodes. Which step should be taken to resolve the issue?

Accepted Answer

Resize the cluster to a larger node type or add more nodes. Option A is correct because RA3 nodes use managed storage; resizing the cluster to a different node type or adding more nodes can increase storage capacity. Option B is wrong because VACUUM reorganizes data but does not free space if the disk is full; it may even require temporary space. Option C is wrong because Analytics is not a feature that affects storage. Option D is wrong because disabling concurrency scaling does not free disk space.

Answer

Disable concurrency scaling to free up resources

Answer

Run a VACUUM command to reclaim space from deleted rows

Answer

Enable Redshift Spectrum to offload queries to S3