DBS-C01 Practice Exam 67 — 20 Questions

Question 1

A company is designing a database for an IoT application that ingests millions of time-series data points per second. The database must support high-throughput writes and efficient querying of recent data. Which AWS database service is MOST suitable?

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

Accepted Answer

Amazon Timestream. Amazon Timestream is purpose-built for time-series data, offering a serverless architecture that ingests millions of data points per second with automatic scaling. It provides efficient storage and querying of recent data through its memory store, while tiering older data to a cost-optimized magnetic store, making it the most suitable choice for high-throughput IoT time-series workloads.

Answer

Amazon RDS for PostgreSQL

Answer

Amazon DynamoDB with TTL

Answer

Amazon Redshift

Question 2

A company uses Amazon DynamoDB to store user session data for a web application. The table has a partition key of 'user_id' and no sort key. Each item is about 5 KB. The application performs frequent GetItem and UpdateItem operations. Recently, the application has been experiencing higher than expected latency and some throttling. The table's read and write capacity are set to on-demand mode. The CloudWatch metrics show that the ConsumedWriteCapacityUnits are well below the provisioned limits (if they were provisioned), but there are occasional ThrottledWriteEvents. The application team also notices that the throttling occurs for specific users. What is the most likely cause and solution?

Accepted Answer

Implement write sharding by appending a random suffix to the partition key for high-traffic users.. Implement write sharding by appending a random suffix to the partition key for high-traffic users. In DynamoDB on-demand mode, each partition can handle up to 3000 read request units or 1000 write request units per second. When a single partition key (user_id) receives high write traffic, that partition can become a hot partition and be throttled, even though overall consumption is within limits. Write sharding distributes the writes for a hot user across multiple partition key values by adding a random suffix to the user_id, thereby spreading the load across multiple partitions. Option A (creating a GSI) would not solve the base table write throttling because the base table writes still target the same partition. Option B (adding a sort key) does not change the partition key distribution; the partition key remains the same, so the hot partition issue persists. Option D (switching to provisioned capacity) would not automatically solve the hot partition; it would require proper partition design similarly.

Answer

Create a global secondary index with a different partition key for the hot users.

Answer

Add a sort key to the table to improve data distribution.

Answer

Switch to provisioned capacity mode and increase the write capacity units significantly.

Question 3

A company is running an Amazon Aurora MySQL database cluster. The database specialist notices that the write latency is high during peak hours. The cluster consists of one writer and two reader instances. Which action should the specialist take to reduce write latency?

Accepted Answer

Increase the instance class of the writer instance to a larger size.. Increasing the instance class of the writer instance provides more CPU and memory resources, which can directly improve write throughput and reduce write latency during peak loads. Option A is incorrect because Auto Scaling in Aurora adjusts the number of reader instances, not the writer capacity. Option C is incorrect because Multi-AZ is already inherent in Aurora; enabling Multi-AZ does not affect write latency. Option D is incorrect because adding more reader instances distributes read traffic but does not reduce write latency on the writer.

Answer

Enable Auto Scaling on the cluster to automatically adjust capacity.

Answer

Enable Multi-AZ deployment for the cluster.

Answer

Add more reader instances to distribute the read load.

Question 4

A developer is troubleshooting a slow query on Amazon RDS for MySQL. The query joins three large tables and runs frequently. What is the most effective way to identify the bottleneck?

Accepted Answer

Enable the slow query log and analyze the output. Enabling the slow query log on RDS for MySQL captures queries that exceed a specified execution time, allowing the developer to identify which queries are slow and analyze their execution plan to find bottlenecks. Option A is wrong because RDS Events are for maintenance and operational notifications, not query performance. Option B is wrong because CloudWatch CPU and memory metrics show overall resource utilization but do not pinpoint specific slow queries. Option D is wrong because migrating to a larger instance may help but does not directly identify the bottleneck; it addresses symptoms rather than root cause analysis.

Answer

Check the RDS Events for any maintenance notifications

Answer

Review Amazon CloudWatch CPU and memory metrics

Answer

Use AWS Database Migration Service to migrate to a larger instance

Question 5

A company is using Amazon DynamoDB with auto scaling for read and write capacity. During a traffic spike, write requests are being throttled even though the table's write capacity is below the maximum limit. Which TWO actions should the team take to resolve the throttling?

Accepted Answer

Review the table's partition key design to ensure even distribution of write traffic. A suboptimal partition key can cause a hot partition, leading to throttling even when overall table capacity is not exhausted. Option E is correct because DynamoDB auto scaling has a lag in provisioning capacity; pre-warming by manually increasing write capacity before a spike can prevent throttling. Option A is incorrect because DynamoDB Streams offloads data but does not increase write capacity. Option B is incorrect because global tables replicate data across regions but do not resolve local hot partitions or capacity lag. Option D is incorrect because reducing read capacity does not increase write capacity.

Answer

Enable DynamoDB Streams on the table to offload writes to a Lambda function

Answer

Create a DynamoDB global table to distribute writes across regions

Answer

Decrease the read capacity to free up resources for writes

Question 6

A company is using Amazon DynamoDB for a gaming leaderboard. The table has a partition key of 'game_id' and a sort key of 'score'. The table is configured with on-demand capacity. During a major tournament, the application experiences high latency and some requests return 'ProvisionedThroughputExceededException' errors. The CloudWatch metric 'ThrottledRequests' spikes. The application uses a single partition key for all writes during the tournament (game_id = 'tournament_final'). What is the most likely cause of the throttling, and what is the best solution?

Accepted Answer

The application is using a single partition key, causing all writes to go to one partition. The team should redesign the partition key to distribute writes across multiple partitions. Even with on-demand capacity, each partition has a maximum throughput limit (read/write capacity per partition). When all writes use the same partition key ('tournament_final'), they all go to a single partition, exceeding its limit and causing throttling (ThrottledRequests and ProvisionedThroughputExceededException). The best solution is to redesign the partition key to distribute writes across multiple partitions (e.g., add a suffix like user_id or timestamp). Option B is incorrect because DAX is a caching layer for reads, not writes; it does not alleviate write throttling. Option C is incorrect because the question does not mention a GSI, and a GSI would not cause this issue on the base table. Option D is incorrect because switching to provisioned capacity does not solve the hot partition problem; the same partition key would still overload a single partition under provisioned capacity.

Answer

The application is using a single partition key, causing all writes to go to one partition. The team should implement DAX to cache writes

Answer

The table has a global secondary index that is throttling writes; the team should remove the GSI

Answer

The table is using on-demand capacity, which has a maximum throughput limit per partition; the team should switch to provisioned capacity with auto scaling

Question 7

A data analytics company runs Amazon Redshift clusters. A user reports that a complex query is taking much longer than expected. The DBA uses the STL_QUERY view to check the query execution. Which column in STL_QUERY should the DBA examine to identify if the query is waiting for resources?

Accepted Answer

service_class. The 'service_class' column indicates the workload management (WLM) queue assigned to the query, which can help identify if the query was queued or waiting for resources. Option A is wrong because 'aborted' indicates whether the query was aborted, not waiting. Option B is wrong because 'query' is just the query ID. Option C is wrong because 'starttime' shows when the query started, not waiting status.

Answer

aborted

Answer

query

Answer

starttime

Question 8

Refer to the exhibit. An IAM policy is attached to a user. The user reports that they cannot delete the production-db database. Which statement best explains the behavior?

Accepted Answer

An explicit Deny statement prevents the deletion of the production-db instance. The IAM policy includes an explicit Deny statement that specifically denies the DeleteDBInstance action on the production-db instance. In IAM, an explicit Deny overrides any Allow, so even if other statements allow DeleteDBInstance, this Deny prevents the deletion. Option B is incorrect because the policy does allow DeleteDBInstance on other resources, so the issue is not a lack of general permissions. Option C is incorrect because the policy includes Allow on DescribeDBInstances. Option D is incorrect because the policy does not restrict CreateDBInstance; the problem is specific to deletion of production-db.

Answer

The user needs additional permissions to delete any DB instance

Answer

The user does not have permission to describe DB instances

Answer

The user does not have permission to create a DB instance

Question 9

A company runs a customer relationship management (CRM) application on Amazon RDS for PostgreSQL. The application stores customer data in a table with over 50 million rows. The company recently added a new query that searches for customers by their email domain (e.g., '@example.com'). The query uses a LIKE pattern: 'WHERE email LIKE ''%@example.com'''. The query takes over 30 seconds to complete. The DBA has already created a B-tree index on the email column, but it does not help. Which action should the database specialist recommend to improve query performance?

Accepted Answer

Create a trigram index (using pg_trgm extension) on the email column.. The query uses a leading wildcard LIKE pattern ('%@example.com'), which prevents a standard B-tree index from being used because the search string does not have a fixed prefix. A trigram index, provided by the pg_trgm extension, breaks strings into three-character substrings (trigrams) and allows the database to efficiently match patterns with leading wildcards. This index type is specifically designed for fuzzy text matching and LIKE queries with wildcards, reducing the query time from over 30 seconds to milliseconds.

Answer

Create a hash index on the email column.

Answer

Increase the shared_buffers parameter to improve caching.

Answer

Create a B-tree index on the reversed email string.

Question 10

A company is deploying a new multi-AZ Amazon RDS for PostgreSQL database. The security team requires that all traffic to the database be encrypted in transit. Which configuration ensures this?

Accepted Answer

Enable SSL/TLS and require client connections to use SSL. Enabling SSL/TLS on the RDS instance and requiring client connections to use SSL ensures that all data transmitted between clients and the database is encrypted in transit. This is achieved by setting the rds.force_ssl parameter to 1 in the DB parameter group, which enforces SSL/TLS for all connections, meeting the security team's requirement for encryption in transit.

Answer

Use a customer master key (CMK) for RDS

Answer

Place the RDS instance in a public subnet

Answer

Enable encryption at rest using AWS KMS

Question 11

A company is using DynamoDB with a VPC endpoint. They want to restrict access to only requests originating from their VPC. Which policy condition should be used?

Accepted Answer

'aws:SourceVpce': 'vpce-12345678'. The 'aws:SourceVpce' condition key allows you to restrict access to requests originating from a specific VPC endpoint (interface endpoint) in your VPC. This ensures that only traffic coming through that VPC endpoint can access the DynamoDB table, providing a network-level security boundary. The condition must reference the exact VPC endpoint ID (e.g., 'vpce-12345678') to enforce this restriction.

Answer

'aws:VpcSourceIp': '10.0.0.0/16'

Answer

's3:x-amz-server-side-encryption': 'AES256'

Answer

'aws:SourceVpc': 'vpc-12345678'

Question 12

A company needs to migrate an on-premises Oracle database to AWS with minimal changes to the application code. The application uses complex stored procedures and has high availability requirements. Which database service should be used?

Accepted Answer

Amazon RDS for Oracle. Amazon RDS for Oracle is the correct choice because it provides native Oracle compatibility, supporting complex stored procedures, PL/SQL, and existing application code with minimal changes. It also offers Multi-AZ deployments for high availability, meeting the requirement without requiring a complete rewrite.

Answer

Amazon DynamoDB

Answer

Amazon Redshift

Answer

Amazon Aurora PostgreSQL

Question 13

Refer to the exhibit. An engineer runs the CLI command to check security groups attached to the RDS instance 'mydb'. The output shows only one security group. The engineer wants to ensure that only traffic from an application server with IP 10.0.1.5 is allowed to the database port 3306. Which security group rule should be added?

Accepted Answer

Add an inbound rule to allow traffic from 10.0.1.5/32 on port 3306.. To allow only the specific IP 10.0.1.5 to access the database, an inbound rule must be added to the security group allowing traffic on port 3306 (MySQL/Aurora) from source 10.0.1.5/32. Option B is correct. Option A is incorrect because it uses port 80 (HTTP) instead of the database port. Option C is incorrect because an outbound rule controls egress, not ingress; inbound rules are needed to allow incoming connections to the database. Option D is incorrect because it allows traffic from any IP (0.0.0.0/0), which is insecure and would violate the requirement to restrict access to a single IP.

Answer

Add an inbound rule to allow traffic from 10.0.1.5/32 on port 80.

Answer

Add an outbound rule to allow traffic to 10.0.1.5 on port 3306.

Answer

Add an inbound rule to allow traffic from 0.0.0.0/0 on port 3306.

Question 14

A company runs a multi-tenant SaaS platform on AWS. Each tenant has their own database schema within a shared PostgreSQL database on Amazon RDS. The platform has grown to thousands of tenants, and the single RDS instance is experiencing performance degradation due to resource contention. Queries from one tenant can impact others. The company needs a solution that isolates tenants, provides predictable performance, and allows easy scaling. They also want to minimize application changes. The application uses an ORM that dynamically constructs SQL queries based on the tenant ID. Which solution is BEST?

Accepted Answer

Create separate RDS instances for each tenant and use RDS Proxy to pool connections per tenant. Modify the application to select the appropriate database instance based on tenant ID.. The best solution because it provides full tenant isolation by assigning each tenant a separate RDS instance, eliminating resource contention and ensuring predictable performance. RDS Proxy efficiently manages connection pooling for each instance, reducing overhead. The application change is minimal: the ORM can be configured to dynamically select the correct database instance based on the tenant ID, preserving the existing SQL-based logic. In contrast, Option A (Aurora Auto Scaling) still shares a single database, offering no isolation. Option C (RDS Proxy on the existing instance) also fails to isolate tenants. Option D (DynamoDB) would require a complete rewrite of the data layer, violating the requirement to minimize application changes.

Answer

Migrate to Amazon Aurora PostgreSQL and use Aurora Auto Scaling to add reader nodes as needed.

Answer

Implement Amazon RDS Proxy in front of the existing RDS instance to manage connections and reduce contention.

Answer

Migrate the application to use Amazon DynamoDB with tenant ID as the partition key, using global tables for scalability.

Question 15

A company is migrating its on-premises PostgreSQL database to Amazon Aurora PostgreSQL. The migration must have minimal downtime. Which THREE steps should be taken as part of the migration plan? (Select THREE.)

Accepted Answer

Perform a test migration to validate the process.. Performing a test migration validates the entire process, including schema compatibility, data integrity, and replication lag, before the actual cutover. This reduces the risk of unexpected failures during the live migration, which is critical for achieving minimal downtime.

Answer

Enable Multi-AZ on the Aurora cluster before migration.

Answer

Disable automated backups on the Aurora cluster to improve performance.

Question 16

A company is migrating a 500 GB on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The migration must have minimal downtime and support ongoing replication after the initial load. Which AWS service should be used?

Accepted Answer

AWS Database Migration Service (DMS) with ongoing replication. AWS Database Migration Service (DMS) with ongoing replication (change data capture, CDC) is required because the scenario demands minimal downtime and continuous synchronization after the initial 500 GB load. DMS uses transaction logs (e.g., PostgreSQL WAL) to capture and apply ongoing changes, enabling a near-zero-duration cutover. Full load only (Option B) would cause downtime during the final sync and cannot support ongoing replication.

Answer

AWS Schema Conversion Tool (SCT)

Answer

AWS Database Migration Service (DMS) with full load only

Answer

AWS Glue

Question 17

A company is using an RDS for MySQL DB instance encrypted at rest with AWS KMS. The security team requires that all access to the database be logged, including queries that fail due to authentication errors. Which configuration meets this requirement?

Accepted Answer

Enable the RDS audit log by setting the 'audit_log_enabled' parameter to 1 in the DB parameter group and export logs to CloudWatch Logs.. RDS for MySQL supports audit logs that can capture authentication failures and queries. By setting the 'audit_log_enabled' parameter to 1 in the DB parameter group and exporting logs to CloudWatch Logs, you meet the requirement to log all access including failed authentication attempts. Option B is incorrect because Enhanced Monitoring provides OS-level metrics, not query logs. Option C is incorrect because AWS CloudTrail logs control plane API calls for RDS, not data plane activities like database queries. Option D is incorrect because S3 server access logs capture requests made to S3 buckets, not database connections.

Answer

Enable RDS Enhanced Monitoring and publish metrics to CloudWatch.

Answer

Enable AWS CloudTrail for the RDS instance and store logs in S3.

Answer

Use S3 server access logs to capture database connection attempts.

Question 18

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.. Enabling Performance Insights provides 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 B 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 19

A company is using an Amazon RDS for MySQL DB instance to store sensitive customer data. A security audit reveals that all database traffic between the application and the database is transmitted in plaintext. Which configuration change would encrypt data in transit for new connections?

Accepted Answer

Modify the DB instance to require SSL/TLS connections and update the application connection string to use SSL.. To encrypt data in transit for new connections to an Amazon RDS for MySQL DB instance, you must modify the DB instance to require SSL/TLS connections. This forces all connections to use SSL/TLS, encrypting the data transmitted between the application and the database. After enabling this, the application connection string must be updated to use SSL (e.g., by adding ssl=true or equivalent). The other options do not encrypt data in transit: VPC peering (B) does not encrypt traffic; encryption at rest using AWS KMS (C) only protects stored data; and IAM database authentication (D) manages authentication but does not encrypt the connection itself.

Answer

Configure the DB instance to be in a VPC with a VPC peering connection to the application's VPC.

Answer

Enable encryption at rest for the RDS DB instance using AWS KMS.

Answer

Enable IAM database authentication for the DB instance.

Question 20

A multinational e-commerce company runs an Amazon Aurora MySQL database for its product catalog. The database is 2 TB and has a high write volume. The company needs to create a test environment that contains a subset (10%) of the production data for developers to use. The test environment must be refreshed daily with the latest production data. The operations team wants to minimize cost and ensure that the test environment does not impact production performance. Which solution should they implement?

Accepted Answer

Use Aurora cloning to create a clone of the production cluster. Use database triggers or scripts to delete 90% of the data after cloning.. Using Aurora cloning creates a storage-level copy that shares the same underlying storage as the source cluster, minimizing cost and avoiding any performance impact on production because cloning does not involve copying data. After cloning, you can delete 90% of the data using scripts or triggers to retain only 10% for testing. Option A (DMS continuous replication) would incur additional cost and ongoing replication overhead. Option B (snapshot and restore) would create a full 2 TB copy and then you would have to delete data, incurring storage costs for the full copy. Option D (read replica) would impact production replication and would also require deleting data after promotion.

Answer

Use AWS DMS to continuously replicate a filtered subset of data to a test cluster.

Answer

Take a manual snapshot of the production cluster, restore it to a new cluster, and delete 90% of the data.

Answer

Create a read replica of the production cluster, promote it to a standalone cluster, and delete 90% of the data.