DBS-C01 Practice Test 9 — 10 Questions

Question 1

A company is using Amazon RDS for MySQL with a cross-Region read replica to support disaster recovery. The primary DB instance is in us-west-2, and the read replica is in us-east-1. The read replica is used for reporting and also serves as a failover target. The operations team notices that the read replica lag is consistently above 10 seconds during peak hours. What should the team do to reduce replica lag?

Accepted Answer

Increase the DB instance class of the read replica.. Increasing the DB instance class of the read replica provides more CPU and memory resources, which allows the replica to apply changes from the binary log more quickly. Cross-Region replication lag is often caused by the replica being unable to keep up with the write rate on the primary, so scaling up the replica directly addresses the bottleneck in applying binlog events.

Answer

Enable Multi-AZ on the primary DB instance.

Answer

Increase the backup retention period for the primary DB instance.

Answer

Disable binary logging (binlog) on the primary DB instance.

Question 2

A company is using an Amazon Aurora MySQL DB cluster. The company wants to implement a backup strategy that supports point-in-time recovery (PITR) with a recovery time objective (RTO) of 15 minutes and a recovery point objective (RPO) of 5 minutes. Which TWO actions should the company take?

Accepted Answer

Configure automated backups with a retention period of at least 5 minutes beyond the current time.. Option A is correct because Aurora automated backups are continuous and incremental, and the retention period must be set to at least 1 day (not 5 minutes) to enable point-in-time recovery (PITR). However, the key insight is that automated backups are always enabled by default with a 1-day retention, and PITR can restore to any point within that retention window, supporting an RPO of 5 minutes as Aurora's backup process captures changes every 5 minutes. Option E is correct because Aurora Backtrack allows you to 'rewind' the cluster to a specific point in time without restoring from a backup, achieving an RTO of 15 minutes or less by directly moving the cluster to a previous state, provided Backtrack is enabled with a backtrack window of at least 5 minutes.

Answer

Create manual snapshots every 5 minutes.

Answer

Enable cross-Region replication for the cluster.

Answer

Enable parallel query for the cluster.

Question 3

A company is using Amazon ElastiCache for Redis to cache frequently accessed data from an RDS MySQL database. The cache hit ratio is currently 85%. The operations team notices that during traffic spikes, the cache eviction rate increases significantly, and the database CPU utilization spikes. The cache cluster uses a single r6g.large node. Which THREE actions should the team take to improve performance? (Choose three.)

Accepted Answer

Add more shards to the cluster to increase total memory.. Option A is correct because adding more shards to the cluster increases the total available memory, which reduces the frequency of evictions during traffic spikes. With more memory, the cache can store more data without forcing out existing entries, thereby maintaining a higher cache hit ratio and reducing the load on the RDS MySQL database.

Answer

Reduce the time-to-live (TTL) for cached items to free up memory faster.

Answer

Configure the cache to use lazy loading only for write-through operations.

Question 4

A database engineer is troubleshooting slow query performance on an Amazon RDS for PostgreSQL instance. The instance is db.r5.large with 500 GB of General Purpose SSD (gp2) storage. CloudWatch metrics show high Read Latency and high Read IOPS, but low CPU utilization. Which TWO actions should the engineer take to improve performance?

Accepted Answer

Create a read replica and offload read queries to it.. A is correct because creating a read replica offloads read queries from the primary instance, reducing the read IOPS and read latency on the primary. This directly addresses the high Read Latency and high Read IOPS metrics without requiring a larger instance class or storage change, especially since CPU utilization is low, indicating the bottleneck is I/O, not compute.

Answer

Increase the DB instance class to a larger size, such as db.r5.2xlarge.

Answer

Enable Multi-AZ to use the standby for read traffic.

Answer

Optimize queries by adding appropriate indexes.

Question 5

A database administrator runs the above AWS CLI command to troubleshoot replication issues. The DB instance 'mydb' is a read replica of 'my-source-db'. The administrator notices that the replica lag is increasing. Which of the following is the MOST likely cause?

Accepted Answer

The read replica is in a different AWS Region than the source.. Option D is correct because when a read replica is in a different AWS Region than the source, the replication traffic must traverse the public internet or a VPN connection, introducing network latency and potential bandwidth constraints. This cross-region lag is a common cause of increasing replica lag, as the asynchronous MySQL replication relies on a single I/O thread to download the binary log events from the source, and any network delay directly impacts the replica's ability to keep up.

Answer

The source DB instance is running a different MySQL version.

Answer

The read replica has Multi-AZ disabled.

Answer

The read replica is using a smaller instance class than the source.

Question 6

A company runs an Amazon Aurora MySQL database cluster with a primary instance and two Aurora Replicas. The application is experiencing occasional deadlocks on the primary instance during peak hours. The deadlocks cause transaction rollbacks that impact customer experience. Which design change should the company implement to minimize deadlocks?

Accepted Answer

Enable Aurora Auto Scaling for read replicas and offload read-only queries to replicas.. Option A is correct because offloading read-only queries to Aurora Replicas reduces the volume of read-write contention on the primary instance. Deadlocks often arise when concurrent transactions compete for the same resources; by directing read traffic to replicas, the primary handles fewer overlapping transactions, lowering the probability of lock conflicts. Aurora Replicas share the same underlying storage volume and serve read traffic without blocking writes on the primary, making this a targeted solution for deadlock reduction.

Answer

Set the transaction isolation level to READ UNCOMMITTED to avoid locks.

Answer

Configure Multi-AZ deployment to automatically failover during deadlocks.

Answer

Increase the DB instance class size to handle more concurrent transactions.

Question 7

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 application performs a query to retrieve the top 10 scores for a given game_id. The query uses ScanIndexForward: false and Limit: 10. Recently, the query response time has increased. The table's read capacity is 1000 RCU, and the average item size is 1 KB. Which is the most likely cause of the increased latency?

Accepted Answer

A hot partition on the game_id key is causing throttling for that specific partition.. The increased latency is most likely due to a hot partition on the 'game_id' key. When a specific game_id receives a disproportionate amount of write or read traffic, that single partition can exceed its throughput limits (1/1000th of provisioned RCU per partition), causing throttling and retries that degrade query response time. Even though the query uses ScanIndexForward: false and Limit: 10, the request is still constrained by the partition's capacity, and throttling at the partition level leads to increased latency.

Answer

The table lacks a global secondary index on game_id, causing a full table scan.

Answer

The query is using strongly consistent reads instead of eventually consistent reads.

Answer

The provisioned read capacity is too low for the query pattern.

Question 8

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.. Option D is correct because 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 9

An organization is using Amazon DynamoDB with on-demand capacity. They notice that the 'ThrottledRequests' metric is non-zero during a specific hour each day. The table stores session data and has a partition key of 'user_id'. The workload is uniform. What is the most likely cause of throttling?

Accepted Answer

The partition key is not evenly distributed.. Option D is correct because the 'ThrottledRequests' metric indicates that requests are being throttled due to partition-level capacity limits. Even with on-demand capacity, DynamoDB imposes a per-partition throughput limit (typically 1,000 WCU or 3,000 RCU per partition). If the partition key 'user_id' is not evenly distributed, a single partition can become a hot key, exceeding its limit and causing throttling despite the table having on-demand capacity.

Answer

The table has on-demand capacity and cannot throttle.

Answer

The account-level read/write capacity limit is exceeded.

Answer

A global secondary index is consuming write capacity.

Question 10

A company is using Amazon RDS for MySQL and notices that the Read IOPS metric is consistently high during business hours. The application is read-heavy. Which configuration change would most likely reduce Read IOPS?

Accepted Answer

Create one or more read replicas and redirect read traffic to them.. Creating read replicas offloads read queries from the primary DB instance to replica instances, directly reducing the number of read I/O operations on the primary. Since the application is read-heavy and Read IOPS is high during business hours, distributing read traffic to replicas alleviates the I/O bottleneck on the primary instance without requiring a larger instance or storage changes.

Answer

Add a Multi-AZ standby instance.

Answer

Increase the DB instance size to a larger instance type.

Answer

Enable storage Auto Scaling on the RDS instance.