DBS-C01 Practice Exam 54 — 20 Questions

Question 1

A company is using Amazon Neptune to run graph queries. The cluster has one writer and two reader instances. After a major version upgrade, the query performance degrades for complex traversal queries. The database specialist suspects that the query optimizer is not using indexes effectively. Which action should the specialist take to identify the issue?

Accepted Answer

Enable the Neptune explain plan feature and review the output.. Option C is correct because enabling the Neptune Query Language (SPARQL or Gremlin) explain plan can show how queries are executed and whether indexes are used. Option A is incorrect because instance metrics show system health, not query execution details. Option B is incorrect because removing indexes would worsen performance. Option D is incorrect because adding readers does not fix query optimization.

Answer

Drop and recreate all indexes to ensure they are up to date.

Answer

Add more reader instances to distribute the query load.

Answer

Check the CloudWatch metrics for CPU utilization and query latency.

Question 2

A development team is using Amazon DynamoDB with on-demand capacity mode for a new application. During initial testing, they notice that write requests are occasionally throttled during traffic bursts. They have enabled DynamoDB Accelerator (DAX) for read-heavy operations. What is the best recommendation to eliminate write throttling?

Accepted Answer

Review the table's partition key design to avoid hot keys.. Option D is correct because on-demand capacity can handle spikes, but if throttling still occurs, there may be a hot partition. Option A is wrong because DAX only caches reads. Option B is wrong because adaptive capacity helps but may not eliminate throttling for extremely skewed access. Option C is wrong because on-demand is already enabled; throttling indicates a design issue.

Answer

Enable DynamoDB adaptive capacity to automatically adjust partition throughput.

Answer

Switch to provisioned capacity mode with Auto Scaling.

Answer

Increase the DAX cluster node size to handle more write traffic.

Question 3

A company uses Amazon Aurora MySQL-Compatible Edition. The database specialist notices that the DB cluster's failover time is longer than expected. The primary instance is using a db.r5.large instance class. Which change would most likely reduce the failover time?

Accepted Answer

Use a larger instance class for the Aurora Replicas.. Using a larger instance class for Aurora replicas ensures they can handle the workload after failover, potentially reducing failover time. However, the key factor is that Aurora failover is typically fast, but if replicas are undersized, the time to promote and become fully operational increases. Using a larger instance class for the replicas (or all instances) can help.

Answer

Enable Backtrack on the DB cluster.

Answer

Increase the number of Aurora Replicas.

Answer

Enable Multi-AZ deployment for the DB cluster.

Question 4

A company is running an Amazon RDS for MySQL DB instance with Multi-AZ deployment. The database experiences a failover due to a hardware failure. After the failover, the application team reports that a critical stored procedure is missing. What should the database administrator do to prevent this issue in the future?

Accepted Answer

Ensure that the stored procedure is created on both the primary and standby instances by using a script or manually recreating it after failover.. Option D is correct because the default_db_character_set and default_collation_for_utf8 are not the cause; the stored procedure is missing because it was created on the primary and not replicated. Using a custom DB parameter group does not replicate stored procedures; they are stored in the database and should be replicated via binlog. Stored procedures are not automatically replicated in RDS MySQL; the best practice is to ensure they are created on both instances or use a script to recreate them after failover. Option A is incorrect because modifying the DB parameter group does not replicate stored procedures. Option B is incorrect because binlog retention does not affect stored procedure replication. Option C is incorrect because creating the stored procedure as a function does not change replication behavior.

Answer

Create the stored procedure as a function instead.

Answer

Modify the DB parameter group to enable binary logging.

Answer

Increase the binlog retention period to ensure the stored procedure is captured.

Question 5

A company is using Amazon DynamoDB with on-demand capacity mode. The application experiences occasional throttling during traffic spikes. The database administrator wants to implement a solution to reduce throttling. Which THREE actions should the administrator take? (Choose THREE.)

Accepted Answer

Use DynamoDB Accelerator (DAX) to cache frequently accessed items.. Options A, C, and D are correct. Implementing retry logic with exponential backoff handles throttling gracefully. Using DynamoDB Accelerator (DAX) reduces read load on the table, which can help with read throttling. Designing the application to handle throttling by retrying ensures resilience. Option B is incorrect because switching to provisioned capacity may not be cost-effective and does not inherently reduce throttling. Option E is incorrect because enabling auto scaling is not applicable to on-demand mode.

Answer

Enable auto scaling for the table.

Answer

Switch the table to provisioned capacity mode with auto scaling.

Question 6

Refer to the exhibit. An application on an EC2 instance is trying to read an object from the S3 bucket 'data-lake-prod'. The instance is in a VPC with an IP address of 10.0.1.5. The application receives an Access Denied error. What is the cause?

Accepted Answer

A Deny statement with a source IP condition is blocking access.. Option B is correct. The Deny statement applies to the source IP 10.0.1.5 (within 10.0.0.0/8), overriding the Allow. Option A is wrong because the IAM role does allow s3:GetObject on the bucket. Option C is wrong because there is no explicit condition on the Allow statement. Option D is wrong because the policy is attached to the role, not an SCP.

Answer

An SCP is denying S3 access to the account.

Answer

The S3 bucket policy requires a specific VPC endpoint.

Answer

The IAM role does not have permission to read from the bucket.

Question 7

A database administrator is troubleshooting a sudden increase in read latency on an Amazon RDS for PostgreSQL instance. The instance has 200 GB of General Purpose SSD (gp2) storage with 600 provisioned IOPS. The administrator notices that the average queue depth is consistently above 4. Which action is the MOST effective way to reduce read latency?

Accepted Answer

Migrate to an io1 volume with 3000 provisioned IOPS.. Option A increases IOPS by scaling up to an io1 volume, which directly addresses the queue depth issue and improves latency. Option B is incorrect because increasing instance size may not resolve IOPS bottleneck. Option C is incorrect because Multi-AZ does not improve read performance for a single instance. Option D is incorrect because increasing storage alone does not guarantee more IOPS for gp2.

Answer

Enable Multi-AZ deployment to offload reads to the standby.

Answer

Change the instance type to a larger size with more vCPUs.

Answer

Increase the allocated storage to 500 GB without changing IOPS.

Question 8

Which THREE of the following are best practices for managing Amazon DynamoDB tables with provisioned throughput?

Accepted Answer

Use a composite key design with a sort key to enable efficient querying.. Options B, C, and D are correct. Option A is incorrect because adaptive capacity automatically handles uneven access patterns; manual partition splitting is not possible. Option E is incorrect because DynamoDB does not maintain indexes for all attributes; GSIs must be created explicitly.

Answer

Create a global secondary index on every attribute to support any query pattern.

Answer

Split hot partitions manually to distribute write traffic.

Question 9

A company is using Amazon DynamoDB with provisioned capacity and Auto Scaling. They notice that during a marketing campaign, write traffic exceeded the provisioned WCU and caused throttling. Auto Scaling increased the WCU, but the throttling persisted for several minutes. Which additional measure can prevent throttling during such predictable spikes?

Accepted Answer

Configure a scheduled scaling action in Application Auto Scaling to increase WCU before the campaign.. Option A is correct because using Application Auto Scaling scheduled scaling allows pre-scaling capacity before the spike. Option B is wrong because DAX is for reads. Option C is wrong because on-demand may be costlier but solves unpredictability; for predictable spikes, scheduled scaling is better. Option D is wrong because increasing max capacity alone doesn't pre-scale.

Answer

Switch the table to on-demand capacity mode.

Answer

Enable DynamoDB Accelerator (DAX) to cache write requests.

Answer

Increase the maximum provisioned WCU in the Auto Scaling policy.

Question 10

A database administrator needs to track changes to an Amazon RDS DB instance's configuration, such as modifications to the DB instance class or security group. Which AWS service should be used?

Accepted Answer

AWS Config. Option B is correct because AWS Config records configuration changes to RDS instances. Option A is wrong because CloudTrail records API calls, not configuration state. Option C is wrong because CloudWatch Logs are for log data, not config changes. Option D is wrong because Systems Manager Patch Manager is for patching.

Answer

Amazon CloudWatch Logs

Answer

AWS CloudTrail

Answer

AWS Systems Manager Patch Manager

Question 11

A database administrator sees the above error logs in CloudWatch for an Amazon RDS for PostgreSQL DB instance. The application team confirms that the password for 'app_user' is correct. What is the most likely cause of the authentication failures?

Accepted Answer

The host '10.0.1.50' is not listed in the pg_hba.conf file.. The errors show authentication failures from a specific host. If the password is correct, the most likely cause is that the host is not allowed by the pg_hba.conf configuration. RDS for PostgreSQL uses DB parameter groups to control pg_hba.conf rules; the rds.force_ssl parameter or the pg_hba.conf entries may not include that host.

Answer

The password has expired for 'app_user'.

Answer

The user 'app_user' does not have the LOGIN privilege.

Answer

The database is in read-only mode.

Question 12

A company is using Amazon Redshift for data warehousing. They notice that query performance has degraded over time. The database administrator checks the system tables and finds that there is significant skew in data distribution across slices. What action should be taken to improve query performance?

Accepted Answer

Recreate the table with a different distribution style, such as KEY distribution on a column with high cardinality.. Option D is correct because data skew causes some slices to have more data than others, leading to slower queries. Recreating the table with a different distribution style can help. Option A is incorrect because vacuum reclaims space and analyzes statistics, but does not fix data skew. Option B is incorrect because modifying sort keys can improve query performance but does not address data skew. Option C is incorrect because adding more nodes does not automatically redistribute existing data; skew persists.

Answer

Increase the number of nodes in the cluster.

Answer

Run the VACUUM command to reclaim space and update statistics.

Answer

Modify the sort keys to better match the query patterns.

Question 13

Refer to the exhibit. A database administrator is writing an IAM policy to manage Amazon RDS snapshots. The policy allows actions on all RDS resources but denies deletion of any DB instance with the prefix 'production-'. A developer attempts to delete a snapshot named 'production-snapshot-2020'. Will this action be allowed?

Accepted Answer

Yes, because the Deny statement only applies to deleting DB instances, not snapshots.. Option B is correct because the 'Deny' statement only applies to the 'rds:DeleteDBInstance' action, not to 'rds:DeleteDBSnapshot'. The 'Allow' statement explicitly allows 'rds:DeleteDBSnapshot' on all resources. Since there is no explicit deny for deleting snapshots, the allow takes effect. Option A is incorrect because the deny only applies to deleting instances, not snapshots. Option C is incorrect because the policy does not deny snapshot deletion. Option D is incorrect because the developer is allowed to delete snapshots.

Answer

Yes, but only if the developer has the necessary permissions.

Answer

No, because the Deny statement overrides the Allow statement.

Answer

No, because the snapshot name starts with 'production-', which matches the resource pattern in the Deny statement.

Question 14

A company's RDS for SQL Server instance has been running for 3 years. The DBA notices that the DB instance's allocated storage (500 GB) is 80% full. The application is write-heavy. The DBA needs to increase storage without downtime. What is the most efficient way to achieve this?

Accepted Answer

Use the Modify DB Instance API to increase allocated storage.. Option C is correct. RDS supports modifying storage without downtime for SQL Server if the storage type supports it. Option A is wrong because creating a new instance involves downtime. Option B is wrong because you cannot attach EBS directly to RDS. Option D is wrong because restoring from snapshot takes time and may require downtime.

Answer

Attach an additional EBS volume to the DB instance.

Answer

Create a new DB instance with larger storage and migrate data.

Answer

Take a snapshot and restore a new instance with larger storage.

Question 15

A developer accidentally deleted a critical table from an Amazon RDS for MySQL DB instance. Automated backups are enabled with a retention period of 7 days. The deletion occurred 3 hours ago. Which action can restore the table with minimal data loss?

Accepted Answer

Perform a point-in-time restore to a time just before the deletion.. Option B is correct because point-in-time recovery can restore to a time before the deletion. Option A is incorrect because restoring from the latest snapshot would lose transactions after the snapshot. Option C is incorrect because the table cannot be restored directly; the whole instance must be restored. Option D is incorrect because DMS is for migration, not recovery.

Answer

Use AWS Database Migration Service to replicate the table from another source.

Answer

Restore the DB instance from the latest automated snapshot.

Answer

Use the MySQL binary log to replay transactions up to the deletion.

Question 16

A database administrator notices that Amazon RDS for MySQL is experiencing high CPU utilization during peak hours. The application is read-heavy with many SELECT queries. Which action is most cost-effective to improve performance?

Accepted Answer

Create one or more read replicas and direct read traffic to them.. Option C is correct because read replicas offload read traffic from the primary, reducing CPU utilization. Option A is wrong because increasing instance size is more expensive and may not be optimal. Option B is wrong because vertical scaling is not the most cost-effective. Option D is wrong because adding storage does not reduce CPU.

Answer

Increase the DB instance class to a larger size.

Answer

Increase the allocated storage to improve I/O throughput.

Answer

Scale up the DB instance vertically to a higher vCPU count.

Question 17

A company uses Amazon DynamoDB for a gaming application. During a new game launch, the application experiences high latency and throttling on a table with a partition key of 'user_id' and a sort key of 'timestamp'. The access pattern is to query recent items for a given user. Which TWO design changes can improve performance?

Accepted Answer

Use a composite key with 'game_id' as partition key and 'timestamp' as sort key.. Option A is correct because using a Global Secondary Index (GSI) with a different key can distribute traffic. Option D is correct because adding a GSI with 'game_id' as partition key can distribute writes if 'game_id' has high cardinality. Option B is wrong because increasing read capacity doesn't solve hot partition issues. Option C is wrong because simple queries are fine. Option E is wrong because DAX caches reads, not writes.

Answer

Use strongly consistent reads for all queries.

Answer

Increase the provisioned read capacity for the table.

Answer

Enable DynamoDB Accelerator (DAX) to cache write operations.

Question 18

A database administrator runs the 'describe-db-clusters' CLI command and sees the above output. The earliest restorable time is December 1, 2023. However, the backup retention period is 7 days. Why is the earliest restorable time earlier than 7 days from now (assuming today is December 5, 2023)?

Accepted Answer

Automated backups are only kept for 7 days, but manual snapshots extend the recovery window.. The earliest restorable time is the earliest point to which you can restore. With a backup retention period of 7 days, the earliest point should be 7 days before the latest restorable time. In this case, the latest restorable time is December 5, so the earliest should be November 28. But it shows December 1, which is only 4 days before. This is because manual snapshots or other factors can extend the restorable range. Actually, the earliest restorable time is determined by the oldest backup (automated or manual) plus transaction logs. If manual snapshots are taken, they can extend the range. The most likely reason is that there are manual snapshots taken before the automated backup window.

Answer

The backup retention period is misconfigured; it should be 30 days.

Answer

The cluster was created on December 1, so that is the earliest point available.

Answer

The 'earliestRestorableTime' is calculated based on the latest transaction log, not backup retention.

Question 19

A company is using Amazon DynamoDB with global tables. The application writes to a table in the us-east-1 region. The database administrator notices that updates made in us-east-1 are not appearing in the replica table in eu-west-1. What is the most likely cause?

Accepted Answer

DynamoDB Streams are not enabled on the table.. Option C is correct because global tables rely on DynamoDB Streams to replicate changes. If streams are disabled, replication stops. Option A is incorrect because DynamoDB does not have a replication delay setting. Option B is incorrect because IAM permissions would cause errors, not silent failure. Option D is incorrect because point-in-time recovery does not affect replication.

Answer

The replication delay is set too high.

Answer

Point-in-time recovery is not enabled on the replica table.

Answer

The IAM role for replication does not have sufficient permissions.

Question 20

A company is using Amazon DynamoDB with on-demand capacity. The application experiences increased latency during peak hours. The DynamoDB table receives about 5,000 writes per second and 10,000 reads per second. The read latency is high, but write latency is acceptable. What should the company do to reduce read latency?

Accepted Answer

Enable DynamoDB Accelerator (DAX) for the table.. Option A is correct. DynamoDB Accelerator (DAX) is a fully managed, highly available, in-memory cache that reduces read latency. Option B is wrong because auto scaling is for provisioned capacity, not on-demand. Option C is wrong because read replicas are not a DynamoDB feature. Option D is wrong because DynamoDB Streams does not cache data.

Answer

Enable DynamoDB Streams to offload read traffic.

Answer

Create a read replica of the DynamoDB table.

Answer

Switch to provisioned capacity and enable auto scaling.