DBS-C01 Practice Exam 67 — 20 Questions

Question 1

A company has an Amazon Aurora MySQL DB cluster with one writer and two readers. The application is experiencing high read latency. CloudWatch shows that the 'AuroraBinlogReplicaLag' metric is high for one of the reader instances. What is the most likely cause?

Accepted Answer

The reader instance is not keeping up with the write workload from the writer. Option A is correct because high binlog replication lag on a reader indicates that the reader is falling behind in applying changes from the writer. Option B is wrong because instance size affects performance but not specifically lag. Option C is wrong because storage is shared across all instances in Aurora. Option D is wrong because parameter groups are shared across the cluster.

Answer

The Aurora cluster storage is experiencing high I/O latency

Answer

The reader instance is undersized and needs to be scaled up

Answer

The DB cluster parameter group is misconfigured

Question 2

A company is experiencing slow query performance on an Amazon RDS for PostgreSQL DB instance. The DB instance is a db.r5.large with 16 GB RAM and 500 GB gp2 storage. Which metric in Amazon CloudWatch would most directly help identify if the performance issue is due to memory pressure?

Accepted Answer

Monitor FreeableMemory to see if available memory is low.. FreeableMemory shows the amount of available RAM. Low FreeableMemory indicates memory pressure, which can cause swapping and slow queries. Option A is wrong because CPUUtilization measures CPU, not memory. Option B is wrong because DatabaseConnections tracks connections, not memory. Option C is wrong because ReadIOPS measures I/O operations, not memory.

Answer

Monitor ReadIOPS to see if there is a high I/O rate due to swapping.

Answer

Monitor DatabaseConnections to check for a high number of connections consuming memory.

Answer

Monitor CPUUtilization to check for high CPU usage.

Question 3

A company is using Amazon DynamoDB with auto scaling enabled. The table has a provisioned read capacity of 10,000 RCU and write capacity of 5,000 WCU. Auto scaling target utilization is 70%. The table experiences a sudden spike in read traffic, reaching 12,000 RCU. The table throttles some requests. Which THREE actions should the company take to prevent future throttling?

Accepted Answer

Implement exponential backoff in the application to retry throttled requests.. Option A is correct because increasing the maximum read capacity prevents throttling. Option B is correct because enabling DynamoDB Accelerator (DAX) reduces read load. Option E is correct because implementing exponential backoff helps handle throttling gracefully. Option C is wrong because decreasing target utilization would cause auto scaling to scale out earlier, but it would not prevent throttling during spikes because auto scaling reacts after the spike. Option D is wrong because write capacity is not the issue.

Answer

Decrease the auto scaling target utilization to 50% to scale out earlier.

Answer

Increase the write capacity to 10,000 WCU.

Question 4

An Amazon DynamoDB table is experiencing throttled write requests. The table uses provisioned capacity with auto-scaling enabled. Which THREE factors could contribute to throttling despite auto-scaling?

Accepted Answer

Auto-scaling maximum capacity is set too low. Options A, B, and D are correct. Auto-scaling cannot handle sudden bursts (A), hot partitions (B), or exceeded max capacity (D). Option C is wrong because eventual consistency doesn't cause throttling. Option E is wrong because GSI consumes write capacity from the table.

Answer

Global secondary index is defined with same partition key

Answer

Use of eventually consistent reads

Question 5

A company is running a MongoDB database on Amazon EC2. The database is experiencing high disk I/O latency. Which AWS service can be used to monitor the disk I/O metrics at the instance level?

Accepted Answer

Amazon CloudWatch. Option C is correct because CloudWatch provides disk I/O metrics for EC2 instances. Option A is wrong because RDS is for managed databases. Option B is wrong because DynamoDB is NoSQL. Option D is wrong because S3 is object storage.

Answer

Amazon RDS

Answer

Amazon DynamoDB

Answer

Amazon S3

Question 6

A company is using Amazon DynamoDB with global tables. The application is experiencing high write latency in one region. Which THREE factors could contribute to this issue? (Choose three.)

Accepted Answer

Replication lag from global tables causing write conflicts.. Option A (network latency), Option C (throttling due to insufficient write capacity), and Option D (replication lag) are correct. Option B is wrong because auto scaling doesn't increase latency; it adds capacity. Option E is wrong because read capacity affects reads, not writes.

Answer

Insufficient read capacity units provisioned for the table.

Answer

The table's auto scaling configuration is set to increase write capacity too aggressively.

Question 7

A company uses Amazon Aurora MySQL for its e-commerce platform. The DB cluster has one writer and two readers. Recently, the application started showing occasional deadlock errors during order processing. The error logs show: 'Transaction (Process ID 123) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.' The application retries three times before failing. The development team wants to reduce the likelihood of deadlocks. Which three actions should the team take? (Choose three.)

Accepted Answer

Shorten the duration of transactions by committing frequently.. Options A, C, and D are correct. Option A: Reducing transaction duration minimizes the window for lock conflicts. Option C: Accessing tables in a consistent order avoids cycle dependencies. Option D: Using READ COMMITTED reduces shared locks for reads. Option B is incorrect because increasing retries does not prevent deadlocks; it only delays failure. Option E is incorrect because lowering isolation level to READ UNCOMMITTED can cause dirty reads and is not recommended for e-commerce.

Answer

Switch to READ UNCOMMITTED isolation level to reduce locking.

Answer

Increase the number of retry attempts to 10.

Question 8

A startup 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 frequently queries the top 10 scores for a given game. Recently, users have reported that the leaderboard is showing stale data. The DBA checks the CloudWatch metrics and sees no throttling. The table has auto scaling enabled. The application uses eventual consistent reads. The DBA suspects that the issue is related to write conflicts. What should the DBA do to ensure the leaderboard shows the most recent data?

Accepted Answer

Modify the application to use strongly consistent reads for leaderboard queries.. Option B is correct because using strongly consistent reads ensures the latest data is read. Option A is wrong because increasing WCU does not affect consistency. Option C is wrong because DAX caches data and may serve stale data. Option D is wrong because DynamoDB Streams are for change data capture, not consistency.

Answer

Enable DynamoDB Streams and process updates in near-real-time.

Answer

Enable DynamoDB Accelerator (DAX) for caching.

Answer

Increase the write capacity units to reduce write throttling.

Question 9

A company uses Amazon DynamoDB Global Tables for a multi-region application. The table is configured with on-demand capacity. The application writes data in the us-east-1 region and reads from us-west-2. Users in us-west-2 report that data written in us-east-1 is not appearing in us-west-2 within the expected replication latency of under 5 seconds. Instead, replication sometimes takes up to 30 seconds. Which two factors could be causing this increased replication latency? (Choose two.)

Accepted Answer

High network latency or packet loss between us-east-1 and us-west-2.. Options B and C are correct. Option B: Network latency between regions directly affects replication time. Option C: Large write volumes can cause backpressure on the replication stream. Option A is incorrect because on-demand capacity does not throttle writes; it scales automatically. Option D is incorrect because Global Tables replicate all data to all regions; us-west-2 must receive all writes. Option E is incorrect because read capacity on a replica does not affect replication; replication uses write capacity in the replica region.

Answer

The application is reading from the us-west-2 table before replication completes.

Answer

The read capacity in us-west-2 is insufficient, causing read throttling.

Answer

The on-demand capacity mode is causing write throttling in us-east-1.

Question 10

A developer reports that an application is unable to connect to an Amazon RDS for Oracle database. The security group for the database allows inbound traffic on port 1521 from the application's security group. The database is publicly accessible. What should be checked next?

Accepted Answer

Verify that the DB subnet group includes a public subnet with an internet gateway.. Option A is correct because even if the security group allows traffic, the DB subnet group must be in a public subnet with an internet gateway. Option B is wrong because the issue is connectivity, not backups. Option C is wrong because CloudWatch Logs may not show connection attempts. Option D is wrong because parameter groups don't control network access.

Answer

Check the DB parameter group for the 'remote_listener' parameter.

Answer

Check the automated backup retention period.

Answer

Review the CloudWatch Logs for error logs.

Question 11

A developer notices that an Amazon ElastiCache for Redis cluster is experiencing high latency. The cluster uses a single node. Which CloudWatch metric should be reviewed first to determine if the issue is due to memory pressure?

Accepted Answer

DatabaseMemoryUsagePercentage. Option A is correct because the DatabaseMemoryUsagePercentage metric indicates the percentage of the node's memory used, which can cause latency if high. Option B is wrong because CPUUtilization indicates CPU load, not memory. Option C is wrong because NetworkBytesIn measures incoming network traffic. Option D is wrong because ReplicationLag only applies to clusters with replicas.

Answer

NetworkBytesIn

Answer

ReplicationLag

Answer

CPUUtilization

Question 12

A company's Amazon RDS for PostgreSQL instance is running out of storage. The DB instance has auto-scaling enabled, but the storage did not increase. What is the most likely cause?

Accepted Answer

The storage usage has not reached the maximum allocated storage.. Option C is correct because auto-scaling only triggers when storage usage reaches the maximum allocated storage and there is at least 10% free space remaining. Option A is wrong because Maximum Storage Duration is the maximum time the instance can run on provisioned storage before scaling. Option B is wrong because there is no minimum storage size for scaling. Option D is wrong because storage auto-scaling does not require modification to the DB instance class.

Answer

The DB instance class does not support storage auto-scaling.

Answer

The DB instance is smaller than the minimum storage size for auto-scaling.

Answer

The DB instance has exceeded the Maximum Storage Duration setting.

Question 13

A database administrator notices that an Amazon RDS for Oracle instance has a high number of connections, causing performance degradation. Which tool can be used to identify the active sessions and their queries?

Accepted Answer

Performance Insights. Option D is correct because Performance Insights provides a dashboard to monitor active sessions and the queries they are running. Option A is wrong because AWS CloudTrail logs API calls, not database sessions. Option B is wrong because RDS Enhanced Monitoring provides OS metrics, not database session details. Option C is wrong because Amazon Inspector is a security assessment tool.

Answer

Amazon Inspector

Answer

RDS Enhanced Monitoring

Answer

AWS CloudTrail

Question 14

A company uses Amazon RDS for SQL Server with Multi-AZ deployment. During a failover test, the application experienced a longer downtime than expected. Which monitoring metric should be reviewed to understand the failover duration?

Accepted Answer

FailoverTime. Option B is correct because the FailoverTime metric in CloudWatch measures the time taken for a Multi-AZ failover. Option A is wrong because DatabaseConnections measures the number of connections, not failover time. Option C is wrong because ReplicaLag is for read replicas, not Multi-AZ. Option D is wrong because WriteLatency measures write latency, not failover duration.

Answer

WriteLatency

Answer

DatabaseConnections

Answer

ReplicaLag

Question 15

Which TWO CloudWatch metrics should be monitored to detect storage performance issues for an Amazon RDS for MySQL instance? (Choose two.)

Accepted Answer

WriteIOPS. Option A and Option C are correct. ReadIOPS and WriteIOPS measure the input/output operations per second, which can indicate storage performance issues. Option B (DatabaseConnections) is about connections, not storage performance. Option D (CPUUtilization) is about CPU usage. Option E (NetworkReceiveThroughput) is about network throughput.

Answer

NetworkReceiveThroughput

Answer

DatabaseConnections

Answer

CPUUtilization

Question 16

A company is using Amazon RDS for MySQL with Multi-AZ deployment. The database experiences a sudden increase in latency and the application reports timeouts. CloudWatch shows elevated 'ReadLatency' and 'WriteLatency' metrics, while 'CPUUtilization' and 'DatabaseConnections' remain normal. Which is the MOST likely cause?

Accepted Answer

A large transaction is being processed. Option B is correct because a large transaction can cause increased latency without high CPU or connection count, as it may be waiting on disk I/O or replication. Option A is wrong because Multi-AZ failover is automatic and would show a spike then recovery. Option C is wrong because insufficient storage I/O would show in 'BurstBalance' or 'WriteIOPS' metrics, not just latency. Option D is wrong because normal CPU and connections rule out a runaway query in terms of CPU, though a query could be I/O-bound. However, a large transaction is a common cause of such symptoms.

Answer

A runaway query is consuming CPU resources

Answer

A Multi-AZ failover occurred

Answer

The database has insufficient provisioned IOPS

Question 17

A developer reports that an Amazon RDS for PostgreSQL database instance's storage is full and the instance is in 'storage-full' state. The team wants to resolve this without downtime. Which action should be taken?

Accepted Answer

Modify the DB instance to increase allocated storage. Option A is correct because modifying the allocated storage for an RDS instance is a dynamic operation that can increase storage without downtime. Option B is wrong because deleting old snapshots does not free up storage on the instance. Option C is wrong because creating a read replica requires the source to have available storage. Option D is wrong because rebooting does not free storage.

Answer

Create a read replica and promote it

Answer

Delete old automated snapshots

Answer

Reboot the DB instance

Question 18

A company uses Amazon DynamoDB Global Tables with strong consistent reads. They notice that a write to us-east-1 is not visible in eu-west-1 after several seconds. Which configuration setting is MOST likely causing this behavior?

Accepted Answer

DynamoDB Streams is not enabled on the table. Option A is correct because Global Tables use last writer wins (LWW) conflict resolution by default; if the application writes to both regions simultaneously, the latest write from the region with the highest timestamp wins, but replication is typically sub-second. However, if the 'ReplicationGroup' is misconfigured, replication can be delayed. But the question mentions strong consistency reads, which are not supported for Global Tables (they support eventual consistency only). Actually, strong consistency reads are not available for Global Tables; using them would cause an error. However, the scenario says they notice a delay, which is expected for eventual consistency. Option A is wrong: strong consistency reads are not supported for Global Tables. Option B is correct: strong consistency reads are not supported, but the scenario says they are using them; this would cause an error, not delay. Option C: DynamoDB Streams must be enabled for Global Tables; if disabled, writes would not replicate at all. Option D: Auto Scaling does not affect replication. Given the options, the most likely cause is that DynamoDB Streams is not enabled on the table, which would prevent replication entirely. But the question says 'not visible after several seconds', which suggests eventual consistency delay. Actually, the correct answer is that Global Tables only support eventual consistency, so strong consistency reads are not possible; but the question says they are using them, which might be a misconfiguration. However, typical exam: strong consistency reads on Global Tables are not supported; using them would cause an error, not a delay. So Option B is plausible: they might have requested strong consistency reads on a global table, which would fail. But the scenario says they notice a delay, not an error. I think the intended answer is that Global Tables rely on DynamoDB Streams; if streams are disabled, writes won't replicate. So Option C. Let me re-evaluate: DynamoDB Streams must be enabled for the table to be used in Global Tables. If streams are disabled, writes will not be replicated. That matches the symptom: writes to us-east-1 are not visible in eu-west-1. Option A: LWW is default, but it doesn't cause delay. Option B: Strong consistency reads are not supported for Global Tables, but the scenario says they are using them; it's unclear if that causes delay or error. Option D: Auto Scaling does not affect replication. So Option C is most likely.

Answer

Auto Scaling is configured for write capacity

Answer

Last writer wins (LWW) conflict resolution is disabled

Answer

Strongly consistent reads are used on a global table

Question 19

A company is using Amazon RDS for MySQL with Multi-AZ deployment. The application team reports that write latency has increased significantly over the past hour. CloudWatch shows elevated 'ReadLatency' and 'WriteLatency' metrics. The DB instance is a db.r5.large with 500 GB General Purpose SSD (gp2) storage. Which action is most likely to resolve the issue?

Accepted Answer

Increase the allocated storage size to 1,000 GB. Option C is correct because elevated latency combined with gp2 storage suggests that the I/O credits are exhausted, causing throughput to drop to baseline. Increasing storage size increases baseline IOPS. Option A is wrong because Multi-AZ is already enabled. Option B is wrong because increasing instance size improves compute but does not address storage I/O limits. Option D is wrong because read replicas help read scaling but do not reduce write latency.

Answer

Enable Multi-AZ deployment

Answer

Create a read replica to offload read traffic

Answer

Scale up the DB instance class to db.r5.xlarge

Question 20

A company is troubleshooting an Amazon DynamoDB table that is experiencing high latency. The table uses on-demand capacity. Which TWO steps should be taken to diagnose the issue?

Accepted Answer

Examine CloudWatch metrics for throttling and latency patterns. Option A is correct because CloudWatch metrics can show throttling, latency, and utilization. Option D is correct because DynamoDB Accelerator (DAX) can reduce latency if the issue is high read volume. Option B is wrong because increasing capacity is not needed for on-demand. Option C is wrong because partitions are managed automatically. Option E is wrong because disabling TTL is unrelated.

Answer

Increase the provisioned read capacity

Answer

Disable TTL to reduce write overhead

Answer

Split the table into multiple partitions manually