DBS-C01 Practice Exam 2 — 20 Questions

Question 1

A company runs a data warehouse on Amazon Redshift. The workload has frequent DELETE and UPDATE operations on a large fact table. Over time, query performance degrades. Which maintenance operation should be scheduled regularly to optimize performance?

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

Accepted Answer

Run VACUUM and ANALYZE commands regularly. B is correct because frequent DELETE and UPDATE operations in Redshift create ghost rows and cause table bloat, degrading query performance. Running VACUUM reclaims space and re-sorts rows, while ANALYZE updates table statistics for the query optimizer; together they restore performance without requiring a full table rebuild.

Answer

Run VACUUM FULL during maintenance windows

Answer

Alter the table to use a different DISTKEY

Answer

Drop and recreate the table periodically

Question 2

Which TWO of the following are benefits of using Amazon RDS Proxy? (Choose TWO.)

Accepted Answer

Reduces the number of database connections by pooling them.. Amazon RDS Proxy acts as a connection broker between your application and the database, maintaining a pool of established connections. When the application opens a new connection, RDS Proxy reuses an idle connection from the pool, which reduces the total number of database connections and prevents the database from being overwhelmed. This pooling mechanism directly addresses the issue of connection exhaustion, especially in serverless or highly concurrent environments.

Answer

Automatically encrypts all traffic between the application and the database.

Answer

Provides built-in read/write splitting for read replicas.

Answer

Reduces storage costs by compressing data in transit.

Question 3

A company is running an Amazon RDS for MySQL Multi-AZ DB instance. The primary instance in us-east-1a experiences an unexpected failure. After the automatic failover, the application team reports that write latency has increased significantly. The new primary instance is in us-east-1b. The DB instance class and storage configuration are identical. What is the MOST likely cause of the increased write latency?

Accepted Answer

The application is connecting to the DB instance in a different Availability Zone, increasing network latency.. After failover, the new primary DB instance resides in us-east-1b, while the application likely continues to connect to the original endpoint or is still running in us-east-1a. This cross-AZ network hop introduces additional latency for write operations, as the application must send data over the network between Availability Zones. The DB instance class and storage are identical, so performance differences are not due to hardware changes.

Answer

The DB instance class in us-east-1b is a different size than the original.

Answer

The Multi-AZ configuration uses asynchronous replication, causing higher latency.

Answer

The new primary is in the same Availability Zone as the application, but the standby is in a different AZ, causing synchronous replication overhead.

Question 4

A company's Amazon Aurora MySQL DB cluster is experiencing a failover event. Which THREE metrics in CloudWatch should be examined to understand the cause of the failover?

Accepted Answer

ACUUtilization. (ACUUtilization) is correct because high ACU utilization can indicate resource exhaustion (CPU/memory pressure) that may trigger a failover in Aurora. Option D (DatabaseConnections) is correct because a sudden spike or drop in connections could signal issues like connection exhaustion or application failures that lead to failover. Option E (FailoverCount) is correct because this metric directly tracks the number of failover events; examining the timestamp of the last increment helps correlate with the incident. Option B (ReadLatency) is wrong because while high read latency can be a symptom, it is not a direct cause of failover; Aurora uses different mechanisms for read scaling. Option C (BinLogDiskUsage) is wrong because it relates to binary log storage for replication, not a direct trigger for failover.

Answer

ReadLatency

Answer

BinLogDiskUsage

Question 5

A company is using Amazon RDS for MySQL with automated backups enabled. The security team requires that all backups be encrypted at rest. Which configuration ensures that new automated backups are encrypted?

Accepted Answer

Create a new encrypted DB instance and migrate the data. Automated backups will inherit encryption.. Encryption at rest must be enabled at creation time on an RDS instance. When you enable encryption at rest on a new DB instance, all automated backups, snapshots, and replicas inherit that encryption automatically. Option B is incorrect because you cannot enable encryption at rest on an existing RDS instance after creation; you must create a new encrypted instance and migrate. Option C is incorrect because automated backups are stored in an S3 bucket managed by RDS, but you cannot directly encrypt the bucket or backups separately; encryption is tied to the DB instance. Option D is incorrect because it incorrectly suggests both enabling encryption on the instance and a separate DBSnapshot option; encryption on the instance already covers backups, and there is no separate DBSnapshot option for enabling encryption.

Answer

Modify the DB instance to enable encryption at rest after creation.

Answer

Use AWS KMS to encrypt the S3 bucket where automated backups are stored.

Answer

Enable encryption at rest on the DB instance and also enable encryption on automated backups using the DBSnapshot option.

Question 6

A media company is migrating a 5 TB MongoDB database to Amazon DocumentDB. The migration must have minimal downtime. The source MongoDB uses sharding across 10 shards. Which migration strategy is MOST appropriate?

Accepted Answer

Use AWS DMS with MongoDB as source and DocumentDB as target, enabling CDC. AWS DMS with CDC (Change Data Capture) is the most appropriate strategy because it supports ongoing replication from a sharded MongoDB source to Amazon DocumentDB, enabling near-zero downtime migration. DMS can handle the 5 TB dataset and 10 shards by using the MongoDB oplog to capture changes after the initial full load, ensuring minimal interruption to the media company's operations.

Answer

Use native MongoDB replication to sync to DocumentDB

Answer

Export data to S3 and use AWS Glue to load into DocumentDB

Answer

Use mongoexport to export data and mongoimport to import into DocumentDB

Question 7

A company uses Amazon Redshift for data warehousing. They run a query that joins a large fact table (10 billion rows) with a small dimension table (1 million rows). The query is slow. The distribution style of the fact table is AUTO, and the dimension table has DISTSTYLE ALL. The join key is user_id. What is the MOST likely reason for the poor performance?

Accepted Answer

The fact table's distribution key is not user_id, causing redistribution. When the fact table uses DISTSTYLE AUTO, Redshift may choose a distribution key that is not user_id. When the fact table is distributed on a different key, joining on user_id requires Redshift to redistribute the fact table rows across nodes to match the dimension table's distribution, causing significant network traffic and slower performance. The dimension table with DISTSTYLE ALL is already replicated to all nodes, so the bottleneck is the fact table's distribution mismatch.

Answer

The dimension table does not have a sort key on user_id

Answer

The dimension table uses DISTSTYLE ALL, which is inefficient for joins

Answer

The fact table should have column compression disabled for the join key

Question 8

A company is building a real-time leaderboard for an online game using Amazon DynamoDB. The leaderboard must update scores within seconds and support queries for top 100 players. Which TWO design patterns should be used? (Choose TWO.)

Accepted Answer

Use DynamoDB Streams to trigger a Lambda function that updates a separate leaderboard table.. DynamoDB Streams can capture score updates in near real-time and trigger a Lambda function to maintain a separate leaderboard table optimized for top-100 queries. This decouples the write-heavy game table from the read-heavy leaderboard, ensuring low-latency updates without contention.

Answer

Create a global secondary index on the score attribute for efficient range queries.

Answer

Store the leaderboard in Amazon ElastiCache for Redis for low-latency reads.

Answer

Set the sort key to the score attribute for natural ordering.

Question 9

Refer to the exhibit. A DBA sees the above log entries for an Amazon Aurora MySQL cluster. What is the most likely cause?

Accepted Answer

There is underlying storage corruption. The logs show page corruption and checksum errors, which are classic symptoms of underlying storage corruption in Aurora MySQL. Storage corruption can occur due to hardware failures or software bugs, and Aurora's distributed storage layer can sometimes experience such issues that manifest as corrupted pages. Option B is incorrect because reader lag would show replication delay metrics and possibly 'seconds behind master' warnings, not corruption-related errors. Option C is incorrect because connection exhaustion would generate errors like 'too many connections' or timeouts, not page corruption. Option D is incorrect because a failed backup restore would typically result in errors during the restore process, not ongoing page corruption after the instance is running.

Answer

The reader instance is lagging behind the writer

Answer

The DB instance has run out of connections

Answer

A recent backup restore operation failed

Question 10

A company is using Amazon RDS for MySQL and has enabled Enhanced Monitoring. The database administrator wants to identify the top contributors to disk I/O. Which THREE metrics from Enhanced Monitoring should they examine?

Accepted Answer

DirtyBufferFlushRate. (DirtyBufferFlushRate) is correct because it indicates the rate at which dirty (modified) buffers are flushed from memory to disk, directly contributing to disk writes and I/O. Option D (WriteOps) is correct as it measures the number of write operations performed on disk, a direct contributor to disk I/O. Option E (PhysicalReads) is correct because it represents read operations that actually hit the disk (i.e., cache misses), contributing to disk I/O. Options B (NetworkThroughput) and C (LogicalReads) are incorrect: NetworkThroughput relates to network traffic, not disk I/O; LogicalReads are reads satisfied from the buffer pool (memory), not disk.

Answer

NetworkThroughput

Answer

LogicalReads

Question 11

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. What is the fastest way to restore the deleted table without affecting other tables?

Accepted Answer

Perform a point-in-time restore of the DB instance to a time just before the deletion, then export the table.. Point-in-time recovery (PITR) allows you to restore the entire DB instance to any second within the automated backup retention period (7 days). By restoring to a time just before the deletion, you can then extract the deleted table using mysqldump or SELECT INTO OUTFILE, and import it back into the original instance. This is the fastest method because it leverages existing automated backups without requiring a manual snapshot or waiting for a full restore of a large instance.

Answer

Use the RDS Query Editor to run a flashback query that retrieves the deleted data.

Answer

Restore the DB instance from the latest manual snapshot and extract the table.

Answer

Restore the table from the automated backup using the AWS Management Console table-level restore feature.

Question 12

A company is running a production Amazon DynamoDB table and notices that read requests are being throttled. The table has on-demand capacity mode enabled. Which action should the database specialist take to troubleshoot the throttling?

Accepted Answer

Check the CloudWatch metric 'ThrottledRequests' for the table and review 'SystemErrors' to identify hot partitions.. With on-demand capacity, throttling often results from hot partitions. The CloudWatch metric 'ThrottledRequests' helps detect throttling, and reviewing 'SystemErrors' can indicate partition-level errors, aiding in identifying hot partitions. Option B is incorrect because auto scaling is only supported for provisioned capacity mode, not on-demand. Option C is incorrect because enabling DAX can reduce read load but does not address the root cause of throttling due to hot partitions; it is not a troubleshooting step. Option D is incorrect because switching to provisioned capacity and increasing RCUs is a remediation action, not a troubleshooting action.

Answer

Enable auto scaling on the table to automatically adjust capacity.

Answer

Enable DynamoDB Accelerator (DAX) to reduce read load on the table.

Answer

Switch the table to provisioned capacity mode and increase the read capacity units.

Question 13

The application uses the IAM role to access the 'orders' DynamoDB table. What is the intended effect of this policy?

Accepted Answer

The role can only access items where the partition key matches the principal's identifier. The policy uses a condition key like `dynamodb:LeadingKeys` with a value referencing the principal's identifier (e.g., `${aws:userid}`). This restricts access to only those items in the 'orders' table whose partition key matches the IAM role's unique identifier, enforcing row-level security. The intended effect is fine-grained access control, not full table access or time-based restrictions.

Answer

The role can perform any DynamoDB action on the 'orders' table

Answer

The role can access all items in the table but only during specific times

Answer

The role is denied access to the 'orders' table

Question 14

A database team is migrating an on-premises Oracle database to Amazon Aurora PostgreSQL. The team needs to ensure minimal downtime and data consistency. Which approach should be used?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication using change data capture (CDC). AWS DMS with ongoing replication using change data capture (CDC) is the correct approach because it enables a live migration with minimal downtime. DMS can perform a full load of the Oracle database and then continuously replicate ongoing changes from Oracle to Aurora PostgreSQL, ensuring data consistency at the point of cutover. This method avoids the need for a long maintenance window and supports heterogeneous migrations with automatic schema conversion.

Answer

Use the PostgreSQL foreign data wrapper (FDW) to link the Oracle database

Answer

Use AWS Server Migration Service (SMS) to replicate the database

Answer

Use pg_dump and pg_restore to migrate the data during a maintenance window

Question 15

A company is using Amazon ElastiCache for Redis to cache database query results. The application team reports that cache hit ratio has dropped significantly. What is the first step to investigate?

Accepted Answer

Check the CacheHitRate and Evictions metrics in CloudWatch. When the cache hit ratio drops significantly, the first step is to investigate whether the cache is evicting keys due to memory pressure or if the working set no longer fits. CloudWatch metrics such as `CacheHitRate` and `Evictions` provide immediate visibility into these conditions without requiring direct Redis access. This aligns with the AWS Well-Architected Framework's principle of observability before making configuration changes.

Answer

Run the Redis INFO command to see memory usage

Answer

Review the ElastiCache event logs for node failures

Answer

Check the Redis AOF persistence logs

Question 16

A company is migrating a PostgreSQL database to Amazon RDS for PostgreSQL. They want to automate the deployment of the RDS instance using infrastructure as code. Which AWS service should they use?

Accepted Answer

AWS CloudFormation.. AWS CloudFormation is the correct service for automating the deployment of an RDS for PostgreSQL instance using infrastructure as code. It allows you to define the entire RDS instance configuration—including DB instance class, storage, backup retention, and security groups—in a declarative JSON or YAML template, which can be version-controlled and reused for consistent, repeatable deployments.

Answer

Amazon EC2 Auto Scaling.

Answer

AWS Management Console.

Answer

AWS Command Line Interface (CLI).

Question 17

A company is migrating a 2 TB Oracle database to Amazon Aurora PostgreSQL. The migration must have minimal downtime and support ongoing replication. Which AWS service should be used?

Accepted Answer

AWS Database Migration Service (AWS DMS). AWS Database Migration Service (AWS DMS) is the correct choice because it supports ongoing replication (change data capture, CDC) from an Oracle source to an Amazon Aurora PostgreSQL target, enabling a migration with minimal downtime. DMS can handle a 2 TB database by using a large replication instance and tuning task settings, and it continuously replicates changes until the cutover is complete.

Answer

AWS DataSync

Answer

Amazon S3 Glacier

Answer

AWS Schema Conversion Tool (AWS SCT)

Question 18

A company is migrating an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. They need to minimize downtime and ensure data consistency. Which TWO methods can be used together to achieve this?

Accepted Answer

Use AWS DMS with full load and CDC. AWS DMS with full load and Change Data Capture (CDC) enables a zero-downtime migration by first copying the existing data (full load) and then continuously replicating ongoing changes from the on-premises PostgreSQL source to the Amazon RDS for PostgreSQL target. This ensures data consistency because CDC captures transactions in near real-time using the PostgreSQL logical replication slot mechanism, allowing the target to stay synchronized until the cutover.

Answer

Take a file system snapshot and copy to Amazon EBS

Answer

Use pg_dump and pg_restore

Answer

Export data to Amazon S3 and import using COPY

Question 19

A company is migrating a 2 TB Oracle database from on-premises to Amazon RDS for Oracle. The database has a 4-hour maintenance window and the migration must have minimal downtime. Which AWS service should be used for the migration?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication from the source database.. AWS DMS with ongoing replication (change data capture) is the correct choice because it allows you to perform a full load of the 2 TB Oracle database and then continuously replicate incremental changes from the source to the target RDS instance. This minimizes downtime by enabling a cutover window of minutes rather than hours, which is critical given the 4-hour maintenance window constraint.

Answer

Use AWS Schema Conversion Tool (SCT) to convert the schema and then perform a full data load.

Answer

Create an RDS Cross-Region Read Replica and promote it to a standalone instance.

Answer

Take a full backup of the on-premises database, upload it to S3, and restore it to RDS.

Question 20

Which THREE factors should be considered when choosing between a homogeneous migration and a heterogeneous migration to Amazon RDS? (Select THREE.)

Accepted Answer

Performance requirements of the target database.. A homogeneous migration (e.g., MySQL to RDS MySQL) typically requires minimal schema changes, preserves performance characteristics, and maintains existing licensing costs. A heterogeneous migration (e.g., Oracle to RDS PostgreSQL) requires schema conversion (validating schema compatibility), may require re-architecting to meet performance requirements due to different query optimizers, and can change licensing costs (e.g., eliminating Oracle licenses). Therefore, factors B, D, and E directly influence the choice between homogeneous and heterogeneous migrations.

Answer

Network latency between source and target.

Answer

Amount of application code changes needed.