DBS-C01 Practice Test 36 — 15 Questions

Question 1

An e-commerce company is migrating its PostgreSQL database to Amazon RDS for PostgreSQL. The database has multiple large tables (over 500 GB each) and the migration window is only 2 hours. Which strategy would be MOST effective to meet the time constraint?

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

Accepted Answer

Use AWS DMS with parallel load by splitting tables into multiple tasks.. AWS DMS with parallel load by splitting tables into multiple tasks allows concurrent data transfer across multiple threads, maximizing throughput for large tables. This approach directly addresses the 2-hour migration window by distributing the workload, whereas a single task would be bottlenecked by sequential processing. Parallel load is specifically designed for high-volume migrations where time is critical.

Answer

Use a single DMS task with full LOB mode.

Answer

Increase the RDS instance size and use pg_dump.

Answer

Use AWS SCT to optimize schema and then one DMS task.

Question 2

A developer is receiving timeout errors when connecting to an Amazon ElastiCache for Redis cluster from an Amazon EC2 instance. The security group for the EC2 instance allows outbound traffic to the Redis cluster's security group on port 6379. The Redis cluster's security group does not allow inbound traffic from the EC2 instance. What is the most likely cause of the timeout?

Accepted Answer

The Redis cluster security group does not have an inbound rule allowing traffic from the EC2 security group on port 6379. Security groups are stateful, meaning that if an outbound rule allows traffic, the return traffic is automatically allowed. However, inbound traffic must be explicitly permitted by the target security group. In this scenario, the EC2 instance's security group allows outbound traffic to the Redis cluster's security group on port 6379, but the Redis cluster's security group does not have an inbound rule allowing traffic from the EC2 security group on that port. Therefore, the connection is blocked, causing timeout errors. Option A is incorrect because network ACLs are stateless and would affect both inbound and outbound traffic, but the issue is specifically with security groups. Option C is incorrect because subnet route tables control network routing, not port-level access. Option D is incorrect because ElastiCache for Redis clusters are accessible within the same VPC if proper security group rules are configured.

Answer

The network ACL for the Redis subnet is blocking inbound traffic on port 6379

Answer

The subnet route table does not have a route to the Redis cluster

Answer

The Redis cluster is not accessible from within the same VPC

Question 3

A financial services company uses Amazon RDS for MySQL with Multi-AZ and read replicas. The application suddenly reports increased write latency. The DB instance is a db.r5.large with 300 GB of General Purpose SSD (gp2) storage. CloudWatch metrics show Write IOPS is at 2,500 and Write Latency averages 50 ms. What is the most likely cause?

Accepted Answer

The gp2 volume has exhausted its I/O credit balance.. The gp2 volume's I/O credit balance is exhausted, causing the volume to fall back to its baseline IOPS of 900 for a 300 GB volume (300 GB * 3 IOPS/GB = 900 baseline IOPS). Since the Write IOPS is 2,500, which exceeds the baseline, the volume must use burst credits; once credits are depleted, latency spikes as seen here. This is the classic symptom of a gp2 volume running out of burst credits, leading to increased write latency. Note that the maximum burst IOPS for gp2 volumes up to 1 TB is 3,000, but the baseline is lower.

Answer

The read replica is under-provisioned causing replication lag.

Answer

The Write IOPS has exceeded the gp2 volume's maximum burst IOPS of 3,000.

Answer

Multi-AZ synchronous replication is causing high latency.

Question 4

A company is using Amazon RDS for MySQL with encryption at rest enabled. The security team wants to ensure that the database backups stored in Amazon S3 are also encrypted using a customer-managed KMS key. What should be done to meet this requirement?

Accepted Answer

No additional action is required; RDS automatically uses the same KMS key for backups.. When encryption at rest is enabled on an Amazon RDS for MySQL DB instance, RDS automatically encrypts all backups, including automated backups and snapshots, using the same KMS key that encrypts the DB instance. No additional action is required to encrypt backups with a customer-managed KMS key; the key used for the instance is also used for its backups. This is a fundamental behavior of RDS encryption at rest.

Answer

Create a new KMS key and specify it when creating the DB instance to encrypt backups differently.

Answer

Modify the DB instance to enable backup encryption using a new KMS key.

Answer

Enable default encryption on the S3 bucket where backups are stored.

Question 5

Refer to the exhibit. A database engineer runs the command and receives the above output. The engineer wants to convert the database to Multi-AZ. Which command should be used?

Accepted Answer

aws rds modify-db-instance --db-instance-identifier mydb --multi-az. To convert an existing RDS DB instance to Multi-AZ, you use the modify-db-instance command with the --multi-az flag. This updates the existing instance's deployment configuration without recreating it, and AWS handles the standby replica provisioning.

Answer

aws rds reboot-db-instance --db-instance-identifier mydb --force-failover

Answer

aws rds create-db-instance --db-instance-identifier mydb --multi-az

Answer

aws rds create-db-cluster --db-instance-identifier mydb --multi-az

Question 6

Refer to the exhibit. A company is migrating from an on-premises MySQL database to Amazon RDS for MySQL. The DBA wants to connect to the RDS instance using the endpoint shown. What additional step is required to allow the DBA's client to connect?

Accepted Answer

Modify the security group to allow inbound traffic on port 3306 from the client IP. Amazon RDS security groups act as a virtual firewall controlling inbound and outbound traffic. By default, no inbound traffic is allowed on port 3306 (MySQL). To permit the DBA's client to connect, you must modify the security group associated with the RDS instance to add an inbound rule that allows TCP traffic on port 3306 from the client's IP address (or a range that includes it). Without this rule, the connection is blocked at the network level regardless of other configurations.

Answer

Create a Route 53 record for the endpoint

Answer

Create a MySQL user that matches the client's IP

Answer

Change the RDS instance to be publicly accessible

Question 7

Which THREE factors should be considered when choosing between Amazon DynamoDB and Amazon Aurora for a new application? (Select THREE.)

Accepted Answer

Access patterns (key-value vs relational queries). DynamoDB is optimized for key-value and document access patterns with single-digit millisecond latency at any scale, while Aurora is a relational database designed for SQL queries with joins and complex filtering. The choice between them hinges on whether the application requires simple key-based lookups (DynamoDB) or relational queries with multiple access patterns (Aurora).

Answer

Cost per GB of storage

Answer

Maximum data size per table

Question 8

A healthcare company stores patient records in Amazon DynamoDB. Each record includes a 'patient_id' (partition key) and 'visit_date' (sort key). The company needs to run ad-hoc queries to find all patients seen by a specific doctor within a date range. Which design approach minimizes cost and latency for this query pattern?

Accepted Answer

Create a global secondary index (GSI) with doctor_id as partition key and visit_date as sort key.. A Global Secondary Index (GSI) with doctor_id as the partition key and visit_date as the sort key allows efficient key-based queries for all patients seen by a specific doctor within a date range. This avoids full table scans and filter operations, minimizing both cost (read capacity units) and latency. DynamoDB can directly retrieve the indexed items without scanning the base table.

Answer

Query the base table using a filter expression on doctor_id.

Answer

Create a local secondary index (LSI) with doctor_id as sort key.

Answer

Use a Scan operation with a filter expression for doctor_id and visit_date.

Question 9

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.. High write latency on an Aurora MySQL cluster is typically caused by the writer instance's resource constraints (CPU, memory, or I/O). Increasing the instance class of the writer instance provides more compute and memory resources, which directly improves write throughput and reduces latency. Reader instances and Auto Scaling do not address writer-side write latency because writes only go to 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 10

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. The slow query log captures queries that exceed a defined execution time threshold, including the exact SQL text, execution time, rows examined, and other diagnostic details. For a frequently run three-table join, this is the most direct way to pinpoint which query is slow and how it behaves. CloudWatch metrics and RDS Events do not expose per-query execution detail, so they cannot identify the bottleneck query itself.

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 11

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.

Question 12

A company wants to ensure that an Amazon RDS for MySQL DB instance is encrypted at rest. Which action should be taken to enable encryption for the first time?

Accepted Answer

Create a new encrypted DB instance using AWS KMS.. Encryption at rest for Amazon RDS can only be enabled when creating a new DB instance. To enable encryption for the first time, you must create a new encrypted DB instance using AWS KMS. Option A is incorrect because encryption cannot be enabled on an existing DB instance via the AWS CLI; it requires creating a new instance. Option C is incorrect because there is no rds.encrypted parameter in a DB parameter group; encryption is set at instance creation, not via parameters. Option D is incorrect because modifying an existing DB instance does not allow enabling encryption; you must create a new encrypted instance.

Answer

Enable encryption on the existing DB instance using the AWS CLI.

Answer

Set the rds.encrypted parameter to true in the DB parameter group.

Answer

Modify the existing DB instance and enable encryption.

Question 13

Which TWO actions should be taken to protect sensitive data in an Amazon RDS for Oracle DB instance? (Choose two.)

Accepted Answer

Use Oracle Transparent Data Encryption (TDE) for sensitive columns.. The correct answers are C and E. Option C, using Oracle Transparent Data Encryption (TDE), encrypts sensitive data at the column level within the database. Option E, enabling encryption at rest using AWS KMS, protects data stored on disk. Option A is incorrect because storing credentials in application configuration files is insecure. Option B is incorrect because disabling automated backups does not enhance security. Option D is incorrect because assigning a public IP increases exposure to attacks.

Answer

Store database credentials in the application configuration file.

Answer

Disable automated backups to reduce storage costs.

Answer

Assign a public IP address to the DB instance for easier access.

Question 14

A company is using Amazon Redshift for data warehousing. The database administrator needs to optimize query performance. Which TWO actions should the administrator take? (Choose TWO.)

Accepted Answer

Analyze the tables to update statistics for the query optimizer.. Option B is correct because running ANALYZE (or ANALYZE COMPRESSION/TABLE) updates the table statistics that the Redshift query optimizer relies on to build efficient query plans, and stale statistics are a common cause of poor join and scan performance. Option E is correct because VACUUM reclaims space from deleted rows and re-sorts data according to the sort key, which improves zone-map effectiveness and reduces the amount of data scanned, directly speeding up queries. Option A is not the right optimization action here because adding nodes is a scaling operation that increases cost and does not address statistics or unsorted data, and it is not one of the two recommended tuning steps. Option C is incorrect because cluster encryption is a security feature and has no effect on query performance. Option D is incorrect because disabling compression increases the amount of data read from disk and typically degrades performance rather than reducing CPU overhead.

Answer

Increase the number of nodes in the cluster.

Answer

Enable encryption for the cluster.

Answer

Disable compression on the tables to reduce CPU overhead.

Question 15

A company is deploying an Amazon RDS for MySQL database in a VPC. The database must be accessible only from a specific set of application servers in the same VPC. Which configuration provides the most secure access?

Accepted Answer

Set the security group inbound rule to reference the security group of the application servers. Referencing the application servers' security group as the source in the RDS inbound rule allows traffic only from those specific instances, regardless of IP changes. This follows the AWS security best practice of using security group IDs for fine-grained, stateful access control within a VPC, eliminating reliance on static IP addresses or CIDR ranges.

Answer

Set the security group inbound rule to allow all traffic from the VPC CIDR

Answer

Place the RDS instance in a separate subnet group

Answer

Set the RDS instance to publicly accessible