DBS-C01 Practice Test 42 — 15 Questions

Question 1

A company is using Amazon DynamoDB Accelerator (DAX) to improve read performance. Recently, the cache hit ratio has dropped significantly. The application uses strongly consistent reads. What is the most likely cause of the low cache hit ratio?

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

Accepted Answer

The application is using strongly consistent reads, which bypass the DAX cache. DAX (DynamoDB Accelerator) is designed to cache data for eventually consistent reads only. When an application uses strongly consistent reads, those requests bypass the DAX cache entirely and go directly to DynamoDB, resulting in a low cache hit ratio. Option A is incorrect because low write capacity may cause throttling but does not directly affect the cache hit ratio. Option C is incorrect because having too few nodes can impact performance and availability, but the primary cause of the drop in cache hits is the consistency model mismatch. Option D is incorrect because while a low TTL can reduce cache effectiveness, the key issue here is that strongly consistent reads never use the cache.

Answer

The DynamoDB table's write capacity is too low

Answer

The DAX cluster has too few nodes

Answer

The DAX cluster's TTL is set too low

Question 2

A company is using Amazon RDS for MySQL and needs to monitor for slow queries. Which TWO AWS services can be used to capture and analyze slow query logs? (Choose TWO.)

Accepted Answer

Amazon RDS Performance Insights. Amazon RDS Performance Insights (Option B) provides database performance analysis and can help identify slow queries by visualizing database load. Amazon CloudWatch Logs (Option E) can ingest and analyze RDS slow query logs by streaming them from RDS. Amazon S3 (Option A) is an object storage service, not a monitoring or analysis service. AWS Config (Option C) is for recording configuration changes, not database logs. AWS CloudTrail (Option D) records API calls for governance, not database-level query logs.

Answer

Amazon S3

Answer

AWS Config

Answer

AWS CloudTrail

Question 3

A company is troubleshooting an Amazon DynamoDB table that is throttling write requests. The table has a partition key ('userId') and a sort key ('timestamp'). The 'WriteCapacityUnits' is set to 1000. CloudWatch shows 'ThrottledWriteRequests' but the 'ConsumedWriteCapacityUnits' is only 500. Which TWO actions could resolve the throttling?

Accepted Answer

Add a random suffix to the partition key to distribute writes more evenly. The issue is throttling on write requests despite consumed capacity below provisioned. This indicates a hot partition where one partition receives more writes than its limit (1000 WCU per partition). Option A (add random suffix to partition key) distributes writes across partitions, preventing any single partition from exceeding its limit. Option C (increase write capacity units) can increase the number of partitions, thereby distributing the load and potentially raising the per-partition limit. Option B is incorrect because DAX is a read cache and does not affect write throughput. Option D (Global Tables) does not resolve throttling and may add latency. Option E (removing sort key) does not address partition hotness.

Answer

Enable DynamoDB Accelerator (DAX) to cache writes

Answer

Enable Global Tables to replicate writes across regions

Answer

Remove the sort key and use only a partition key

Question 4

A company is using Amazon DynamoDB and wants to monitor the read/write capacity utilization of a table. Which ONE AWS service can be used to set up alarms for capacity consumption?

Accepted Answer

Amazon CloudWatch. Amazon CloudWatch (D) is the primary service for monitoring DynamoDB capacity metrics such as ConsumedReadCapacityUnits and ConsumedWriteCapacityUnits, and it can trigger alarms based on thresholds. Option C (Amazon CloudWatch Logs) is not used for direct capacity monitoring because DynamoDB does not emit capacity consumption logs; those metrics are available only through CloudWatch Metrics. DynamoDB Auto Scaling (A) adjusts capacity but does not monitor or alarm. AWS CloudTrail (B) records API calls, not capacity metrics. AWS Config (E) tracks configuration changes, not utilization.

Answer

Amazon DynamoDB Auto Scaling

Answer

AWS CloudTrail

Answer

Amazon CloudWatch Logs

Answer

AWS Config

Question 5

A developer reports that an Amazon ElastiCache for Redis cluster's memory usage is consistently above 90%. The application uses Redis for caching and session storage. Which configuration change would MOST effectively reduce memory pressure?

Accepted Answer

Enable eviction with volatile-LRU policy. Enabling eviction with the volatile-LRU policy automatically removes the least recently used keys that have a TTL set, freeing memory without manual intervention. Option B (scaling up) reduces memory pressure but at higher cost; it is not the most effective change since eviction addresses the root cause by discarding stale data. Option C (AOF persistence) writes data to disk, not freeing memory; it can actually increase memory usage during writes. Option D (disabling replication) may free some memory used for replica buffers but does not address the high memory utilization caused by cached data, and it impacts availability.

Answer

Scale up to a larger node type

Answer

Enable AOF persistence to free memory

Answer

Disable replication to reduce memory overhead

Question 6

A company is using Amazon DynamoDB with global tables. The application team reports that data written in one region is not immediately available in another region. The database specialist needs to monitor the replication lag. Which CloudWatch metric should be used?

Accepted Answer

Monitor the 'ReplicationLatency' metric in the replica region.. 'ReplicationLatency' is the CloudWatch metric that measures the time between an update to a DynamoDB global table in the source region and its appearance in the replica region. Option A is wrong because 'ConsumedWriteCapacityUnits' measures the amount of write capacity consumed, not replication lag. Option B is wrong because 'PendingReplicationCount' shows the number of items waiting to be replicated, not the time delay. Option C is wrong because 'ThrottledRequests' indicates that requests are being throttled, which is unrelated to replication lag.

Answer

Monitor the 'ConsumedWriteCapacityUnits' metric in both regions.

Answer

Monitor the 'PendingReplicationCount' metric in the source region.

Answer

Monitor the 'ThrottledRequests' metric in the source region.

Question 7

A company is migrating a 500 GB Oracle database to Amazon RDS for Oracle. The migration must be completed within 24 hours with minimal downtime. The on-premises network bandwidth is 1 Gbps. The migration team plans to use AWS DMS with ongoing replication. During the initial load, the DMS task fails with an error indicating that the source database is experiencing high CPU utilization. The source database is a production system serving live traffic. The team needs to reduce the impact on the source database while still meeting the migration deadline. Which approach should the team take?

Accepted Answer

Reduce the number of tables loaded in parallel in the DMS task and schedule the migration during off-peak hours. The issue is that DMS is consuming too many resources on the source. Reducing the number of tables loaded in parallel and scheduling the migration during off-peak hours will reduce CPU impact. Option B is the most balanced. Option A (increase DMS instance size) would increase source CPU usage. Option C (change to full load only) would require downtime. Option D (use Snowball) may not meet the 24-hour deadline due to shipping time.

Answer

Change the DMS task to perform only full load and skip ongoing replication

Answer

Increase the size of the DMS replication instance to speed up the migration

Answer

Use AWS Snowball to transfer the data offline and then use DMS for ongoing replication

Question 8

A company's Amazon Redshift cluster is experiencing slow query performance. Which THREE diagnostic steps should be taken to identify the bottleneck?

Accepted Answer

Query SVL_QUERY_REPORT to see step-level performance. To diagnose slow query performance in Amazon Redshift, you should query SVL_QUERY_REPORT to view step-level execution details (Option B), STL_QUERY to analyze query execution times (Option C), and STL_WLM_QUERY to check for WLM queue waits (Option D). Option A is incorrect because STL_LOAD_ERRORS is used for data load errors, not performance. Option E is incorrect because STV_BLOCKLIST shows disk block allocation, which is not directly related to query performance.

Answer

Query STL_LOAD_ERRORS to check for data load errors

Answer

Query STV_BLOCKLIST to check disk allocation

Question 9

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 2 TB in size and has a 24/7 uptime requirement. The migration must have minimal downtime and support ongoing replication. Which TWO services or features should the specialist use to accomplish this?

Accepted Answer

An AWS DMS replication instance.. Options C and E are correct. Option C: An AWS DMS replication instance is required to run AWS DMS tasks, including migration with ongoing replication. Option E: AWS DMS with change data capture (CDC) enables ongoing replication with minimal downtime. Option D is incorrect because AWS Schema Conversion Tool (AWS SCT) is used for heterogeneous migrations (e.g., Oracle to PostgreSQL), not for homogeneous Oracle-to-Oracle migrations. Option A is incorrect because Oracle Data Guard is not supported for direct replication to Amazon RDS for Oracle; DMS is used instead. Option B is incorrect because cross-Region automated backups are a backup feature, not a migration tool for minimal downtime migration.

Answer

Oracle Data Guard to replicate to RDS.

Answer

Amazon RDS cross-Region automated backups.

Answer

AWS Schema Conversion Tool (AWS SCT).

Question 10

A company is using Amazon DynamoDB with on-demand capacity. The operations team notices that the number of throttled write requests has increased. Which metric should be monitored to determine if the table's write capacity is being exceeded?

Accepted Answer

WriteThrottleEvents. 'WriteThrottleEvents' is the Amazon CloudWatch metric that directly indicates throttled write requests. Option A is wrong because 'ThrottledWriteRequests' is not a standard CloudWatch metric name (the correct name is WriteThrottleEvents). Option C is wrong because 'ProvisionedWriteCapacityUnits' is not applicable for on-demand capacity. Option D is wrong because 'ConsumedWriteCapacityUnits' shows actual usage, not throttling.

Answer

ThrottledWriteRequests

Answer

ProvisionedWriteCapacityUnits

Answer

ConsumedWriteCapacityUnits

Question 11

A company is using Amazon DynamoDB with on-demand capacity mode. The company notices that during a flash sale, the write requests are throttled. What is the most likely cause of the throttling?

Accepted Answer

A hot partition is causing throttling even though the table uses on-demand capacity.. For a DynamoDB table in on-demand capacity mode, throttling is typically caused by a hot partition. On-demand mode automatically scales table-level throughput, but if a single partition key is heavily accessed (e.g., during a flash sale), that partition can exceed its individual capacity limit, resulting in throttled write requests. This is the most likely cause, making option C correct. Option A (maximum throughput limit) does not apply because on-demand has no fixed maximum; option B (auto scaling) is irrelevant since on-demand manages scaling automatically; option D (provisioned WCUs) is not used in on-demand mode.

Answer

The table has reached its maximum throughput limit for on-demand mode.

Answer

The table is not configured for auto scaling.

Answer

The provisioned write capacity units (WCUs) are set too low.

Question 12

A company is migrating a 5 TB MySQL database to Amazon Aurora MySQL. The migration must have minimal downtime and support ongoing replication. The source database is in a corporate data center with a 500 Mbps internet connection. Which THREE steps should the database specialist take?

Accepted Answer

Use AWS Schema Conversion Tool (AWS SCT) to convert the schema.. Options B, D, and E are correct. Option B: The AWS Schema Conversion Tool (AWS SCT) converts the source MySQL schema to be compatible with Aurora MySQL, which is often necessary due to differences in storage engines or features. Option D: AWS Database Migration Service (AWS DMS) with change data capture (CDC) enables ongoing replication and minimizes downtime by continuously syncing changes from the source database to the target Aurora database. Option E: An AWS Snowball Edge device is used for the initial data load, which transfers the 5 TB database over a fast local connection to AWS, reducing the time required compared to the 500 Mbps internet connection. Option A is incorrect because using a VPN and mysqldump would result in significant downtime and slower data transfer; it does not support ongoing replication. Option C is incorrect because creating an Aurora read replica is not a migration method; read replicas are used for read scaling within a managed Aurora environment, not for migrating data from an external source.

Answer

Establish a VPN connection to AWS and use mysqldump.

Answer

Create an Aurora read replica from the source database.

Question 13

A company uses Amazon ElastiCache for Redis as a caching layer for a database. The cache cluster has one primary and one replica node. During a maintenance event, the primary node fails and the replica is promoted. After promotion, the application experiences increased latency. What should a database specialist do to reduce the impact of future failovers?

Accepted Answer

Enable cluster mode and distribute the cache across multiple shards.. Enabling cluster mode on the ElastiCache for Redis cluster distributes data across multiple shards, each with its own primary and replica nodes. During a failover, only the data in the failed shard's primary needs to be rebuilt, limiting the cache miss impact. Adding more replicas (Option D) does not reduce the latency impact because a single primary still serves all requests after failover, and the new primary must warm its cache from scratch. Disabling replica reads (Option A) would not address the latency increase. Automatic backups (Option B) do not affect runtime performance after failover.

Answer

Disable replica reads to avoid stale data.

Answer

Enable automatic backups with a retention period of 35 days.

Answer

Add more replica nodes to the cluster.

Question 14

A company is running an Amazon RDS for MySQL Multi-AZ DB instance. The company wants to implement a backup strategy that meets a recovery point objective (RPO) of 5 minutes and a recovery time objective (RTO) of 1 hour. Which THREE steps should the company take to meet these objectives?

Accepted Answer

Configure AWS Backup to copy automated backups to another region.. Automated backups with a 35-day retention period (B) enable point-in-time recovery within the last 35 days, supporting an RPO of 5 minutes. Configuring AWS Backup to copy automated backups to another region (A) provides cross-region disaster recovery, helping meet the RTO of 1 hour by restoring in a different region. Creating a cross-region read replica (D) allows for quick failover by promoting the replica, which can significantly reduce RTO. Option C (Single-AZ) is less resilient and does not help meet RPO/RTO. Option E (daily manual snapshots) cannot achieve a 5-minute RPO due to manual timing.

Answer

Change the DB instance to a Single-AZ configuration to reduce costs.

Answer

Take daily manual snapshots and copy them to another region.

Question 15

A company is running an Amazon RDS for SQL Server DB instance. The database administrator needs to perform a major version upgrade. What is the recommended approach to minimize downtime?

Accepted Answer

Use AWS Database Migration Service (DMS) to migrate the database to a new instance with the new version.. For Amazon RDS for SQL Server, creating a Read Replica with a different major version is not supported. Therefore, the recommended approach to minimize downtime is to use AWS Database Migration Service (DMS) to migrate the database to a new instance with the new version. DMS allows for minimal downtime by continuously replicating data and then switching over. Options C and D cause significant downtime during the snapshot/restore or direct upgrade process.

Answer

Create a Read Replica of the DB instance with the new version, promote it to a standalone instance, and then redirect application traffic.

Answer

Take a snapshot of the DB instance and restore it with the new version.

Answer

Modify the DB instance directly and apply the new version during the maintenance window.