DBS-C01 Practice Test 14 — 15 Questions

Question 1

A company is migrating an on-premises Oracle database with complex stored procedures and triggers to AWS. They want to minimize code changes. Which AWS database service should they consider?

Accepted Answer

Amazon RDS for Oracle. Amazon RDS for Oracle is the most direct migration target because it uses the same Oracle Database engine, allowing existing stored procedures, triggers, and PL/SQL code to run with minimal or no modification. Amazon Aurora PostgreSQL with Babelfish is not suitable for Oracle migrations because Babelfish provides compatibility with SQL Server T-SQL, not Oracle PL/SQL. Therefore, only RDS for Oracle minimizes code changes for Oracle stored procedures.

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Amazon DynamoDB

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Amazon S3

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Amazon Redshift

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Amazon Aurora PostgreSQL with Babelfish

Question 2

A company is migrating an on-premises MongoDB database to Amazon DocumentDB (with MongoDB compatibility). The application uses MongoDB's aggregation pipeline with $lookup and $unwind stages. What should the company verify before migration?

Accepted Answer

Check if all aggregation pipeline stages used by the application are supported in DocumentDB.. Amazon DocumentDB (with MongoDB compatibility) does not support all MongoDB aggregation pipeline stages. Specifically, the `$lookup` and `$unwind` stages are supported, but other stages like `$merge`, `$facet`, `$bucket`, `$bucketAuto`, `$graphLookup`, and `$search` are not. Before migration, the company must verify that every stage used in their application's aggregation pipelines is fully supported in DocumentDB to avoid runtime failures.

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Verify that DocumentDB supports sharding for the collection.

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Ensure the application uses the latest MongoDB driver.

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Confirm that the application's secondary indexes can be migrated.

Question 3

A financial services company runs a critical application on Amazon RDS for Oracle. The workload is write-heavy with frequent small transactions. The DBA notices high latency during peak hours. Which design change would best address this?

Accepted Answer

Switch to Provisioned IOPS (io1 or io2) volume type. The workload is write-heavy with frequent small transactions, and high latency during peak hours indicates that the current storage volume is not meeting the IOPS demands. Provisioned IOPS (io1 or io2) volumes provide consistent, low-latency performance by guaranteeing a specific number of IOPS, which directly addresses the bottleneck caused by insufficient I/O capacity for write-intensive operations.

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Implement ElastiCache for Redis

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Enable Multi-AZ deployment

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Add a read replica

Question 4

A financial company uses Amazon DynamoDB to store customer transaction data. The compliance team requires that all data be encrypted at rest using a customer-managed AWS KMS key. Additionally, they need to ensure that the key is used only for DynamoDB and no other AWS service. How can the company meet these requirements?

Accepted Answer

Create a KMS key with a key policy that includes a condition such as "kms:ViaService": "dynamodb.amazonaws.com" to restrict usage to DynamoDB.. The correct approach is to create a KMS key with a key policy that includes a condition like "kms:ViaService": "dynamodb.amazonaws.com" (C). This condition restricts the use of the key to requests that come through the DynamoDB service, ensuring the key is used only for DynamoDB and not other AWS services. This is a precise, least-privilege method to meet the requirement.

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Use a KMS key with no key policy, and rely on IAM policies to restrict access to only DynamoDB.

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Use an AWS Organizations service control policy (SCP) to deny all AWS services except DynamoDB from using the KMS key.

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Create a KMS key with a key policy that allows DynamoDB to use the key, and attach an IAM policy to deny all other services.

Question 5

A company is migrating a 10 TB Oracle database to Amazon Aurora PostgreSQL. The migration uses AWS DMS with CDC. After the full load, the CDC phase is falling behind by several minutes. The source Oracle database generates 500 MB of redo logs per minute. Which action will most likely improve CDC performance?

Accepted Answer

Increase the number of parallel apply threads on the DMS task. Increasing the number of parallel apply threads on the DMS task allows the target Aurora PostgreSQL database to apply changes concurrently, reducing the bottleneck caused by sequential apply. With 500 MB/min of redo logs, the single-threaded default apply cannot keep pace, so parallel apply directly addresses the lag by distributing the load across multiple threads.

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Disable CDC and perform a full load only

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Reduce the batch size in the DMS task settings

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Increase the source Oracle redo log size

Question 6

A company is deploying a new web application that uses Amazon RDS for MySQL. To improve read performance, they add a read replica. However, the application reports stale data. What is the most likely cause?

Accepted Answer

The replication is asynchronous and there is replication lag.. Amazon RDS for MySQL uses asynchronous replication for read replicas. The primary instance commits writes and then sends the binary log (binlog) events to the replica, which applies them. This asynchronous nature introduces replication lag, meaning the replica may not have the most recent writes. If the application reads from the replica before the lag is resolved, it will see stale (older) data.

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The application is using a connection pool that caches connections to the primary.

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The read replica is in a different AWS Region.

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The application is reading from the replica before the write is committed on the primary.

Question 7

Which TWO factors should you consider when choosing between Amazon RDS and Amazon DynamoDB for a new application?

Accepted Answer

RDS requires a predefined schema, while DynamoDB is schema-less.. Option A is correct because Amazon RDS is a relational database service that requires you to define a fixed schema (tables, columns, data types) before storing data, whereas DynamoDB is a NoSQL key-value and document store that is schemaless—each item can have different attributes. Option E is correct because DynamoDB excels with unstructured or semi-structured data at massive scale with single-digit millisecond latency, while RDS is designed for structured data requiring complex joins, transactions, and relational integrity. Option B is wrong because DynamoDB can be accessed over the public internet via its HTTPS endpoint (or privately via VPC endpoints), and RDS can also be made publicly accessible or kept private. Option C is wrong because DynamoDB offers built-in multi-AZ replication automatically, and RDS also supports Multi-AZ deployments. Option D is wrong as a distinguishing factor because while both services do support encryption at rest and in transit, it does not help you choose between them for an application.

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DynamoDB can only be accessed from within a VPC, while RDS can be public.

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Only RDS supports Multi-AZ deployments for high availability.

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Both services support encryption at rest and in transit.

Question 8

A company has a compliance requirement to encrypt all RDS snapshots at rest using a customer-managed KMS key. The RDS instance is already encrypted with an AWS-managed key. What is the correct procedure to ensure snapshots use the customer-managed key?

Accepted Answer

Take a snapshot of the RDS instance, copy the snapshot specifying the customer-managed KMS key, and restore from the copied snapshot.. Because an RDS instance's encryption key cannot be changed after creation, the correct procedure is to take a snapshot of the encrypted instance, copy the snapshot while specifying the customer-managed KMS key (snapshot copy allows re-encryption with a different key), and then restore a new instance from that copied snapshot. This yields an RDS instance whose data and subsequent snapshots are encrypted with the customer-managed key, satisfying the compliance requirement.

Answer

Create a new RDS instance with the customer-managed KMS key and migrate data using DMS.

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Change the default KMS key for the AWS account to the customer-managed key.

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Modify the RDS instance to use the customer-managed KMS key directly.

Question 9

A company is deploying a new Amazon RDS for MySQL database. The security team requires that all data at rest be encrypted. What is the simplest way to meet this requirement?

Accepted Answer

Enable encryption at rest when creating the RDS instance using an AWS KMS key. Amazon RDS for MySQL supports encryption at rest using AWS KMS keys, which must be enabled at instance creation time because encryption cannot be added to an existing unencrypted RDS instance. Option C is correct because it describes the simplest and most direct method: enabling encryption at rest during the initial RDS instance creation with an AWS KMS key, which transparently encrypts the underlying storage, automated backups, read replicas, and snapshots.

Answer

Enable encryption using AWS Certificate Manager

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Use client-side encryption in the application

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Enable encryption at rest on the RDS instance after creation

Question 10

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?

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.

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Amazon RDS for PostgreSQL

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Amazon DynamoDB with TTL

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Amazon Redshift

Question 11

A company uses Amazon Redshift for data warehousing. The security team has implemented column-level security using Redshift's column-level access controls. However, during a security audit, it is discovered that a user with SELECT privilege on a table can still see the content of a column that should be restricted. The column is defined with a GRANT statement that only allows SELECT on certain columns to specific users. What is the most likely cause of this issue?

Accepted Answer

The user was previously granted SELECT on the entire table, and the column-level GRANT did not revoke that broader permission.. In Redshift, column-level GRANTs are additive and do not automatically revoke a pre-existing table-wide SELECT privilege. If the user was previously granted SELECT on the entire table, that broader grant still applies, so the user can read the restricted column despite the narrower column-level grant. The fix is to REVOKE the table-level SELECT first, then grant only the specific columns.

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The column is part of a distribution key that bypasses security controls.

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The user is accessing the table via a stored procedure that bypasses column-level security.

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The column-level security is not supported in Redshift; it must be implemented using views.

Question 12

A company runs a global application using Amazon Aurora Global Database. The primary region is us-east-1, and secondary regions are eu-west-1 and ap-southeast-1. The application reports that writes to the primary are taking longer than expected. What is the most likely cause?

Accepted Answer

The primary DB instance is under-provisioned.. Amazon Aurora Global Database uses asynchronous replication from the primary region to secondary regions. Writes to the primary are committed locally and do not wait for replication to complete. Therefore, replication to secondary regions does not introduce synchronous commit latencies. The most likely cause of slower writes to the primary is an under-provisioned primary DB instance that cannot handle the write workload efficiently.

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Multi-AZ failover occurred in the primary region.

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The Global Database replication to secondary regions is causing synchronous commit latencies.

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Read replicas in secondary regions are overloaded.

Question 13

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. They need to minimize downtime. Which TWO actions should they take?

Accepted Answer

Set up AWS DMS with change data capture (CDC) from the source. Option A is correct because AWS Database Migration Service (DMS) with change data capture (CDC) continuously replicates ongoing changes from the on-premises Oracle source to the RDS target after the initial full load, allowing a short cutover window and thus minimizing downtime. Option C is correct because AWS Schema Conversion Tool (SCT) analyzes and converts the source Oracle schema, stored procedures, and other objects to be compatible with the RDS for Oracle target, catching incompatibilities before migration and preventing failed or delayed cutovers. Option B is not relevant because increasing allocated storage addresses capacity/IOPS, not migration downtime. Option D is wrong because Single-AZ reduces availability and does not simplify or improve replication for a minimal-downtime migration. Option E is wrong because disabling Oracle archivelog mode would break CDC/redo-based replication and risk data loss, not speed up a safe migration.

Answer

Increase the allocated storage on the target RDS instance to improve performance

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Deploy the target RDS instance as a Single-AZ to simplify replication

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Disable Oracle archivelog mode to speed up data transfer

Question 14

A company is running Amazon Redshift for data warehousing. The data warehouse is used for complex analytical queries. Recently, query performance has degraded due to data skew. Which steps should be taken to address this issue?

Accepted Answer

Re-evaluate the distribution style of the tables.. Data skew in Amazon Redshift occurs when data is unevenly distributed across slices, causing some nodes to process more data than others and degrading query performance. Re-evaluating the distribution style (e.g., switching from AUTO or EVEN to KEY on a column with high cardinality and even distribution, or using ALL for small dimension tables) redistributes the data evenly, mitigating skew and improving parallel query execution.

Answer

Apply sort keys on the skewed columns.

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Apply compression on the skewed columns.

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Increase the number of nodes in the cluster.

Question 15

A company runs a critical e-commerce application on Amazon Aurora MySQL with a single DB instance. The database has 8 TB of data and uses the default writer endpoint. Recently, the application experienced a 10-minute outage during a primary instance failover. The failover was triggered by an underlying hardware issue. The database specialist needs to minimize downtime during future failovers. The application team is unwilling to modify the application code to handle connection retries. The company has a 99.99% SLA requirement. Which solution should the database specialist implement to meet the SLA with minimal application changes?

Accepted Answer

Create an Amazon RDS Proxy and configure the application to connect to the proxy endpoint. Amazon RDS Proxy sits between the application and the database, pooling and reusing database connections. During a failover, RDS Proxy maintains the client connections and transparently reconnects to the new primary instance, so the application does not experience a connection loss and does not need to implement retry logic. This directly addresses the 10-minute outage by reducing failover downtime to seconds, meeting the 99.99% SLA without application code changes.

Answer

Increase the DB instance class to a larger size to improve performance and reduce failover time

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Enable Multi-AZ deployment with automatic failover

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Create a cross-Region read replica and promote it to primary during failover