DBS-C01 Mock Exam 84 — 25 Questions

Question 1

A database specialist observes the CloudWatch metric for a production RDS for MySQL instance. The max_connections parameter is set to 150. The Sum of DatabaseConnections over 1-minute periods is shown. The application reports intermittent connection failures. What is the most likely cause?

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

Accepted Answer

The number of connections exceeded the max_connections limit.. The Sum metric over 1-minute period represents the total number of connections during that minute. A Sum of 200 indicates that at some point during the minute, connections exceeded the max_connections of 150, causing failures. Option B is wrong because the metric shows Sum, not average. Option C is wrong because connection pooling reduces connections, not increases. Option D is wrong because the metric clearly shows high connection counts.

Answer

The average number of connections is below the limit.

Answer

The DatabaseConnections metric is unreliable.

Answer

The application is not using connection pooling.

Question 2

A company is running an Amazon Redshift cluster with a single node. They need to improve query performance for large analytical workloads. Which action would provide the most immediate performance improvement?

Accepted Answer

Increase the number of nodes in the cluster.. Adding more nodes to the cluster distributes the workload and improves parallelism. Option A is wrong because using a single node, distributing data across slices is limited. Option B is wrong because compression is already used typically. Option D is wrong because VACUUM reclaims space but does not significantly improve performance for large workloads.

Answer

Distribute the data across all slices.

Answer

Apply compression encodings to all columns.

Answer

Run the VACUUM command to reclaim space.

Question 3

A company is using Amazon DynamoDB for a session management application. The application is experiencing higher latency during peak hours. The DynamoDB table uses on-demand capacity. Which TWO steps should a database specialist take to diagnose the issue?

Accepted Answer

Check the CloudWatch metric for ThrottledRequests to see if any requests are being throttled.. Checking ThrottledRequests helps identify if requests are being throttled, even with on-demand. Reviewing PartitionKey metrics helps detect hot partitions. ReadCapacityUnits and WriteCapacityUnits are not applicable for on-demand. Latency metrics show end-to-end performance but are less diagnostic.

Answer

Review the table's ReadCapacityUnits and WriteCapacityUnits to ensure they are sufficient.

Answer

Examine the CloudWatch metric for UserErrors to identify client-side issues.

Answer

Enable DynamoDB Streams to capture all write events for analysis.

Question 4

Which THREE actions should be taken to troubleshoot a high number of ThrottlingExceptions from Amazon DynamoDB? (Choose 3.)

Accepted Answer

Examine the ConsumedWriteCapacity and ThrottledWriteCount metrics in CloudWatch. A, C, D are correct. Examining CloudWatch metrics helps identify throttling patterns. Implementing exponential backoff is a best practice. Increasing provisioned capacity resolves throttling. B is wrong because enabling DynamoDB Streams does not affect throttling. E is wrong because changing consistency model does not affect write throttling.

Answer

Enable DynamoDB Streams to offload writes

Answer

Change the read consistency to eventual

Question 5

A company uses Amazon RDS for PostgreSQL with Multi-AZ deployment. The primary instance fails, and a failover occurs. After the failover, the application is still unable to connect to the database endpoint. The database administrator checks the RDS console and sees that the new primary is in 'available' state. What should the administrator do next to diagnose the connectivity issue?

Accepted Answer

Check the DNS resolution of the RDS endpoint from the application server. The DNS CNAME of the RDS endpoint should have updated to point to the new primary. If the application is using the old IP or a cached DNS entry, it may not connect. Option A is incorrect because security group rules are usually unchanged. Option B is incorrect because the subnet group is not the issue. Option D is incorrect because the primary is already in available state.

Answer

Verify that the security group for the RDS instance allows inbound traffic from the application

Answer

Check if the subnet group for the RDS instance is correctly configured

Answer

Restart the RDS instance to force a new connection

Question 6

A company uses Amazon DynamoDB with On-Demand capacity for a gaming application. During a new game launch, write traffic spikes 10x normal for 30 minutes. Some write requests receive ProvisionedThroughputExceeded exceptions. What is the MOST likely cause and solution?

Accepted Answer

The partition key is not distributing writes evenly, causing a hot partition. Redesign the partition key for uniform access.. On-Demand capacity can handle spikes but has per-partition throughput limits. If a hot partition exists, writes to that partition may exceed its limit. Option A is correct because uneven partition keys cause throttling. Option B is incorrect because On-Demand does not have table-level limits. Option C is not the primary cause. Option D is incorrect as GSI writes also consume write capacity.

Answer

On-Demand capacity cannot handle sudden spikes. Switch to Provisioned capacity with auto scaling.

Answer

DynamoDB Streams is enabled, causing additional write throttling. Disable streams.

Answer

The table has a global secondary index with a different partition key that is unevenly accessed. Remove the GSI.

Question 7

A database administrator is using AWS DMS to migrate an on-premises Oracle database to Amazon RDS for PostgreSQL. The migration has been running for several hours, but the full load phase is taking much longer than expected. The CPU utilization on the DMS replication instance is consistently below 10%. What is the MOST likely cause of the slow performance?

Accepted Answer

The target RDS instance is throttling write operations due to low IOPS.. When the target RDS instance has insufficient IOPS, write operations are throttled, causing a bottleneck that slows down the full load phase. Even though the DMS replication instance's CPU is low (below 10%), the target database cannot keep up with the incoming data, leading to increased latency and reduced throughput. This is a common performance issue in DMS migrations where the target's provisioned IOPS are exhausted, especially during large data loads.

Answer

The source database has large LOBs that are being transferred in full LOB mode.

Answer

The target database engine is not compatible with DMS.

Answer

The DMS task is not configured to use parallel tables.

Question 8

A company uses Amazon RDS for PostgreSQL with a single-AZ deployment. The operations team needs to ensure that the database is available during a planned maintenance event that requires a reboot. The maintenance window is set for 30 minutes. The database size is 200 GB and the application can tolerate a few minutes of downtime. Which action should the team take to minimize downtime during the reboot?

Accepted Answer

Modify the DB instance to be Multi-AZ. Enabling Multi-AZ on the RDS instance creates a standby in a different Availability Zone. During planned maintenance, Amazon RDS automatically performs a failover to the standby, resulting in minimal downtime (typically under a minute), which meets the requirement of a few minutes of downtime. Option A is incorrect because restoring from a manual snapshot takes much longer than a few minutes and is not an automated failover. Option B is incorrect because promoting a read replica requires manual intervention and the replica may not be fully synchronized, leading to potential data loss and longer downtime. Option C merely schedules the reboot during low traffic but does not reduce the downtime of the reboot itself; the instance still becomes unavailable during the reboot.

Answer

Take a manual snapshot before the maintenance window and restore it if needed

Answer

Create a read replica and promote it to primary after the reboot

Answer

Schedule the reboot during a low-traffic period

Question 9

A company is migrating a 3 TB Oracle database to Amazon Aurora PostgreSQL. The database has a heavy OLTP workload with many small transactions. The migration must have minimal downtime. Which TWO strategies should the company use? (Choose two.)

Accepted Answer

Use AWS DMS with ongoing replication to capture and apply changes.. AWS DMS with ongoing replication (CDC) is the correct strategy because it allows continuous capture and application of changes from the source Oracle database to the target Aurora PostgreSQL, enabling minimal downtime during migration. The heavy OLTP workload with many small transactions is well-suited for DMS's change data capture, which can handle high-volume transactional changes efficiently.

Answer

Convert the database to Amazon Aurora MySQL instead.

Answer

Create an Aurora read replica from the Oracle database.

Answer

Use AWS Schema Conversion Tool (SCT) to convert the schema.

Question 10

A company uses Amazon ElastiCache for Redis as a caching layer for a web application. They observe a sudden increase in CPU utilization on the cache cluster, and the application experiences higher latency. Which action should be taken to diagnose the issue?

Accepted Answer

Monitor Amazon CloudWatch metrics for the ElastiCache cluster to identify the cause.. The first step in diagnosing a sudden CPU utilization increase and latency in ElastiCache is to monitor CloudWatch metrics such as CPUUtilization, CacheHits, CacheMisses, and EngineCPUUtilization to identify patterns or bottlenecks. Option A is incorrect because ElastiCache for Redis does not support query profiling; that feature is for RDS. Option C is incorrect because disabling persistence (e.g., AOF or RDB) reduces durability but is not a diagnostic action and may not address CPU issues. Option D is incorrect because scaling up should only be considered after analyzing metrics to determine if capacity is the actual problem.

Answer

Enable query profiling on the ElastiCache cluster.

Answer

Disable persistence to reduce CPU overhead.

Answer

Immediately scale up to a larger node type.

Question 11

A database administrator notices that an Amazon RDS for MySQL instance's CPU utilization is consistently above 80% during peak hours. The DB instance is a db.r5.large with 16 GB memory and 500 GB gp2 storage. The application is a read-intensive web application. Which action is MOST effective to reduce CPU load without significant cost increase?

Accepted Answer

Create a read replica and redirect read traffic to it. Creating a read replica offloads read traffic from the primary instance, reducing CPU utilization without requiring a larger instance or more storage. Option A increases cost significantly. Option C may not help if the issue is CPU, not I/O. Option D increases storage but does not directly reduce CPU.

Answer

Increase the instance size to db.r5.xlarge

Answer

Enable Performance Insights to identify slow queries and optimize them

Answer

Increase the allocated storage to 1000 GB to improve I/O performance

Question 12

A database specialist is troubleshooting a slow-running query on an Amazon Aurora MySQL DB cluster. The query performs a large table scan. Which THREE actions would likely improve query performance?

Accepted Answer

Increase the size of the DB instance to provide more memory and CPU.. Creating appropriate indexes can speed up queries by avoiding table scans. Increasing the instance size provides more memory and CPU for query execution. Enabling query caching can store results of repeated queries. Changing isolation level and enabling parallel query may not help in all cases and may have side effects.

Answer

Change the transaction isolation level to SERIALIZABLE.

Answer

Enable Aurora Parallel Query to parallelize the table scan.

Question 13

A company is using an Amazon RDS for MySQL database and needs to audit all database login events. The audit logs must be stored in Amazon S3 for long-term retention. Which steps should be taken to accomplish this?

Accepted Answer

Enable the 'audit_log' plugin, publish logs to CloudWatch Logs, and create an export task to S3.. Amazon RDS for MySQL supports the audit_log plugin, which captures login events. These logs can be published to CloudWatch Logs, and then an export task can be created to move them to Amazon S3 for long-term retention. Option A is incorrect because RDS does not allow direct log file copying to S3 via manual methods. Option B is incorrect because CloudTrail data events for RDS capture API calls, not database-level login events. Option C is incorrect because RDS does not natively publish audit logs directly to an S3 bucket; they must go through CloudWatch Logs first.

Answer

Enable the 'general_log' parameter and set 'log_output' to 'FILE', then copy the log file to S3 manually.

Answer

Enable CloudTrail data events for RDS to capture login events and store in S3.

Answer

Enable the 'audit_log' plugin and configure RDS to publish logs to an S3 bucket.

Question 14

A company runs an Amazon Aurora MySQL DB cluster with one writer and two readers. They notice that one reader instance is consistently showing higher than expected lag. The other reader is fine. What is the most likely cause?

Accepted Answer

The reader instance is being used for heavy analytical queries. An imbalanced workload on that reader can cause it to lag. Option A is wrong because writer load affects all replicas. Option B is wrong because network issues would affect both readers. Option D is wrong because parameter group change would affect both readers if applied to cluster.

Answer

The writer instance is experiencing high write activity

Answer

There is a network connectivity issue between the writer and that reader

Answer

The reader instance has a different DB parameter group

Question 15

Refer to the exhibit. A database administrator is reviewing the output of 'SHOW FULL PROCESSLIST' on an Amazon RDS for MySQL DB instance. The company's security policy requires that all database users access only the minimum necessary data. Which user's activity should be investigated further?

Accepted Answer

The admin user, because the query is selecting all columns from the credit_cards table.. The admin user is executing a full scan of the credit_cards table, which is a security concern because it could be accessing unnecessary data. The app_user is querying a specific column with a condition, which is more appropriate. The admin user should have a more restrictive query. Option B is correct. Option A is wrong because the admin user's query is broad. Option C is wrong because the app_user's query is specific. Option D is wrong because both queries are selecting data, but the admin's is more concerning.

Answer

Both users, because they are both accessing the credit_cards table.

Answer

The app_user, because the query is selecting card_number which is sensitive.

Answer

Neither user, because the queries are normal for their roles.

Question 16

A company has an Amazon RDS for MySQL database that contains sensitive data. The security team requires that all data be encrypted at rest using a customer-managed key stored in AWS KMS. Which action should be taken to meet this requirement?

Accepted Answer

Create a new RDS instance with encryption enabled using the KMS key, migrate data, and delete the old instance.. Amazon RDS encryption at rest with a customer-managed KMS key can only be enabled when the DB instance is created. You cannot enable encryption on an existing unencrypted instance (option A is incorrect). Once you create a new encrypted instance using the desired KMS key, you can migrate the data from the old instance and then delete it. Option D is incorrect because restoring a snapshot of an unencrypted database without modifying encryption settings will result in an unencrypted instance; you would need to create an encrypted copy of the snapshot first, which is not described. Option C is incorrect because DB parameter groups do not control encryption at rest.

Answer

Enable encryption on the existing RDS instance by modifying the instance.

Answer

Configure the DB parameter group to require encryption at rest.

Answer

Create a snapshot of the unencrypted database and restore it as an encrypted database.

Question 17

A company is planning to deploy an Amazon RDS for PostgreSQL instance. Which of the following is a required step to enable automated backups?

Accepted Answer

Set the backup retention period to a value greater than 0.. Automated backups in Amazon RDS for PostgreSQL are enabled by setting a backup retention period greater than 0 days. By default, the retention period is 0, which disables automated backups. Once set to a value between 1 and 35 days, RDS automatically takes daily snapshots and retains transaction logs for point-in-time recovery within that window.

Answer

Set a preferred maintenance window.

Answer

Enable encryption at rest.

Answer

Configure a Multi-AZ deployment.

Question 18

A company is using Amazon RDS for MySQL and wants to restrict access to the database based on the source IP address. Which AWS feature should be used to achieve this?

Accepted Answer

VPC Security Groups. Security groups act as a virtual firewall for RDS instances. You can specify inbound rules that allow traffic only from certain IP addresses or other security groups. Network ACLs are for subnets, not individual instances. IAM policies control API access, not network traffic. DB parameter groups configure database engine parameters.

Answer

DB Parameter Groups

Answer

IAM Database Authentication

Answer

Network ACLs

Question 19

A company uses Amazon RDS for MySQL with Multi-AZ and read replicas. The database has a table storing user sessions with 50 million rows. The application team reports that queries using 'SELECT * FROM sessions WHERE user_id = ? ORDER BY login_time DESC LIMIT 10' are slow. The EXPLAIN plan shows a full table scan. Which design change would BEST improve query performance?

Accepted Answer

Create a composite index on (user_id, login_time). The query filters on user_id and orders by login_time, which is a classic case for a composite index. A B-Tree index on (user_id, login_time) allows MySQL to locate all rows for the given user_id via the index's leading column and then retrieve the rows in sorted order using the second column, avoiding a full table scan and a filesort operation. This directly addresses the root cause — the lack of an index to support both the WHERE and ORDER BY clauses efficiently.

Answer

Implement an application-level cache using ElastiCache

Answer

Partition the table by user_id

Answer

Upgrade to a larger instance type with more memory

Question 20

Which TWO are best practices for designing a DynamoDB table for high-traffic e-commerce application? (Select TWO.)

Accepted Answer

Create Global Secondary Indexes to support different access patterns.. Global Secondary Indexes (GSIs) allow you to support multiple query patterns without duplicating data or redesigning the base table. In a high-traffic e-commerce application, you might need to query orders by customer ID, by status, or by date; GSIs provide alternative access patterns with their own partition and sort keys, enabling efficient queries without full table scans.

Answer

Use a constantly increasing value (e.g., timestamp) as the partition key.

Answer

Design the table to use scan operations for most queries.

Answer

Use a single attribute as the partition key with low cardinality.