DBS-C01 Monitoring and Troubleshooting Practice Test 13 — 15 Questions

Question 1

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 2

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 3

A database administrator notices that an Amazon RDS for Oracle DB instance's CPU utilization is consistently above 90% during peak hours. The application is read-heavy. Which action can reduce CPU load?

Accepted Answer

Create a read replica and direct read traffic to it. Option B is correct because creating a read replica offloads read traffic from the primary instance, reducing CPU usage. Option A is wrong because increasing instance size may help but is more costly; also, read replica is a better practice for read-heavy workloads. Option C is wrong because disabling Multi-AZ reduces availability, not CPU. Option D is wrong because enabling Performance Insights adds overhead, not reduces CPU.

Answer

Disable Multi-AZ to free up resources

Answer

Increase the allocated storage

Answer

Enable Performance Insights to optimize queries

Question 4

A company uses Amazon Redshift for data warehousing. They run a daily ETL job that loads data into the cluster. Recently, the job started failing with 'Disk Full' errors. The cluster has 5 RA3 nodes. Which step should be taken to resolve the issue?

Accepted Answer

Resize the cluster to a larger node type or add more nodes. Option A is correct because RA3 nodes use managed storage; resizing the cluster to a different node type or adding more nodes can increase storage capacity. Option B is wrong because VACUUM reorganizes data but does not free space if the disk is full; it may even require temporary space. Option C is wrong because Analytics is not a feature that affects storage. Option D is wrong because disabling concurrency scaling does not free disk space.

Answer

Disable concurrency scaling to free up resources

Answer

Run a VACUUM command to reclaim space from deleted rows

Answer

Enable Redshift Spectrum to offload queries to S3

Question 5

An application uses Amazon ElastiCache for Redis as a session store. Users report that sessions are being lost intermittently. The ElastiCache cluster has replication enabled with one replica. CloudWatch metrics show 'Evictions' spiking during peak hours. What is the MOST likely cause?

Accepted Answer

The cache's memory is full and the eviction policy is removing keys. Option A is correct because evictions occur when memory is full and the cache evicts keys based on the eviction policy. This would cause session loss. Option B is wrong because replication lag would cause stale data, not loss. Option C is wrong because snapshotting may cause latency but not evictions. Option D is wrong because encryption in transit does not affect memory.

Answer

Replication lag between primary and replica is causing read failures

Answer

Encryption in transit is enabled and causes decryption errors

Answer

The cluster is performing automatic snapshots that block writes

Question 6

A company uses Amazon DynamoDB and notices that some queries are taking longer than expected. The table has a partition key only. The 'ConsumedReadCapacityUnits' is below the provisioned throughput. What is the most likely cause of the slow queries?

Accepted Answer

The partition key is not distributed evenly, causing hot partitions. Option C is correct because if the partition key is not chosen well, data can be skewed, causing hot partitions. Even if total consumed capacity is below provisioned, a single partition may receive more requests than its share of capacity, causing throttling on that partition. Option A is wrong because global tables do not cause slow queries on the source table. Option B is wrong because DynamoDB Streams do not affect read latency. Option D is wrong because DAX is a caching layer that speeds up reads, not slows them.

Answer

DAX is misconfigured and slowing down reads

Answer

Global tables replication is causing delays

Answer

DynamoDB Streams is enabled and consuming read capacity

Question 7

A database administrator is troubleshooting an Amazon RDS for SQL Server instance that is experiencing high 'ReadIOPS' and 'ReadLatency'. The instance uses General Purpose SSD (gp2) storage. The 'BurstBalance' metric is 0%. What should the administrator do to improve performance?

Accepted Answer

Increase the allocated storage or switch to Provisioned IOPS. Option D is correct because when BurstBalance is 0%, the gp2 volume has exhausted its burst credits and is operating at baseline IOPS. To improve performance, you can increase the volume size (which increases baseline IOPS) or switch to Provisioned IOPS (io1/io2). Option A is wrong because enabling Multi-AZ does not increase I/O performance. Option B is wrong because disabling backups reduces CPU but not IOPS. Option C is wrong because creating a read replica does not improve write performance.

Answer

Enable Multi-AZ to distribute the load

Answer

Create a read replica to offload read traffic

Answer

Disable automatic backups to reduce I/O

Question 8

A company runs a critical application on Amazon RDS for PostgreSQL. The application team reports that the database occasionally becomes unresponsive for a few seconds. CloudWatch metrics show 'CPUSurplusCreditsCharged' and 'CPUSurplusCredits' are not 0. The instance is a db.t3.medium. What is the likely cause and how should it be fixed?

Accepted Answer

The instance is out of CPU credits and is being throttled; switch to a larger or non-burstable instance. Option A is correct because t3 instances are burstable and use CPU credits. When credits are exhausted, they can use surplus credits, which incur charges. If the workload is consistently high, the instance may run out of credits and become throttled, causing unresponsiveness. The fix is to switch to a T3 unlimited mode (but that incurs charges) or use a non-burstable instance (e.g., m5). Option B is wrong because modifying Multi-AZ does not affect CPU credits. Option C is wrong because enabling Enhanced Monitoring does not fix credit exhaustion. Option D is wrong because storage optimization does not affect CPU credits.

Answer

Enable Enhanced Monitoring to diagnose the issue

Answer

Increase the allocated storage to improve I/O

Answer

The instance is experiencing a failover; enable Multi-AZ

Question 9

A company is troubleshooting an Amazon DynamoDB table that is throttling write requests. The table has a partition key ('userId') and a sort key ('timestamp'). The 'WriteCapacityUnits' is set to 1000. CloudWatch shows 'ThrottledWriteRequests' but the 'ConsumedWriteCapacityUnits' is only 500. Which TWO actions could resolve the throttling?

Accepted Answer

Add a random suffix to the partition key to distribute writes more evenly. Option A is correct because a hot partition can throttle even if overall capacity is underutilized; adjusting the partition key design can distribute writes. Option D is correct because using DynamoDB Accelerator (DAX) can offload read traffic but does not affect writes; actually DAX is for reads. Option B is correct because increasing write capacity ensures enough capacity for peaks. Option C is wrong because removing the sort key changes the table structure and may not help with partition hotness. Option E is wrong because Global Tables replicate writes and may increase throttling. So correct answers: B and E? Let's re-evaluate: The issue is write throttling despite consumed capacity below provisioned. This indicates a hot partition. Option A: Adding a random suffix to partition key helps distribute writes across partitions. Option B: Increasing write capacity may help if the hot partition is still within limits, but if a single partition is throttled due to its own limit, increasing total capacity may increase the partition limit. Actually, DynamoDB's partition capacity is 1000 WCU per partition; if a single partition receives more than 1000 WCU, it throttles. Increasing total WCU may increase the partition count, distributing the load. Option C: Removing the sort key does not affect partition distribution. Option D: DAX is a read cache, not for writes. Option E: Global Tables add more write replication and could increase throttling. So likely correct: A and B. Option A is a design change to avoid hot partition. Option B increases total capacity, which may increase partitions. So answer: A, B.

Answer

Enable DynamoDB Accelerator (DAX) to cache writes

Answer

Enable Global Tables to replicate writes across regions

Answer

Remove the sort key and use only a partition key

Question 10

A database administrator is monitoring an Amazon RDS for MySQL instance and sees the following CloudWatch metrics: 'DiskQueueDepth' is consistently at 10, 'WriteLatency' is 20 ms, 'FreeStorageSpace' is less than 10% of total. The instance uses gp2 storage. Which THREE actions should be taken to improve performance?

Accepted Answer

Switch to Provisioned IOPS (io1 or io2) for consistent performance. Option A is correct because low free space can cause performance degradation on gp2; increasing storage increases baseline IOPS. Option B is correct because high 'DiskQueueDepth' indicates I/O bottleneck; switching to Provisioned IOPS provides consistent I/O. Option C is correct because enabling Multi-AZ does not improve I/O performance, it adds overhead. Option D is wrong because Performance Insights is a monitoring tool, not a fix. Option E is correct because deleting old data frees up space and can improve performance. So correct: A, B, E.

Answer

Enable Multi-AZ to increase I/O capacity

Answer

Enable Performance Insights to identify slow queries

Question 11

A company uses Amazon Redshift and notices that queries are taking longer than usual. CloudWatch metrics show 'CPUUtilization' is high and 'DiskSpace' is low. Which TWO actions can help improve query performance?

Accepted Answer

Add more nodes to the cluster. Option A is correct because adding nodes distributes workload and increases CPU and I/O resources. Option B is wrong because VACUUM reorganizes data but does not free space if the disk is full; it may require space. Option C is correct because optimizing sort keys reduces the amount of data scanned, speeding up queries. Option D is wrong because disabling concurrency scaling reduces performance. Option E is wrong because Multi-AZ is not available for Redshift. So correct: A, C.

Answer

Disable concurrency scaling to free resources

Answer

Enable Multi-AZ to distribute load

Answer

Run VACUUM to reclaim space

Question 12

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 13

A DevOps engineer notices that an Amazon RDS for PostgreSQL instance has been in 'storage-full' state for the past 30 minutes. The instance has 500 GB of General Purpose SSD (gp2) storage, and the free storage space is 0 bytes. The database is critical and cannot tolerate downtime. What is the MOST efficient way to resolve this issue while minimizing downtime?

Accepted Answer

Modify the DB instance to increase allocated storage to 1,000 GB. Option B is correct because modifying storage to 1,000 GB does not require downtime and automatically adds more space. Option A is wrong because deleting logs may not free enough space and requires manual intervention. Option C is wrong because taking a snapshot and restoring to a larger instance causes downtime. Option D is wrong because enabling storage auto-scaling does not immediately solve the current full state.

Answer

Take a snapshot of the DB instance and restore it to a new instance with larger storage

Answer

Enable storage auto-scaling on the DB instance

Answer

Delete unnecessary data, such as old logs or temporary tables

Question 14

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 15

An application running on Amazon EC2 is unable to connect to an Amazon RDS for SQL Server DB instance. The security group for the RDS instance allows inbound traffic from the security group of the EC2 instance on port 1433. The network ACLs allow all traffic. What is a likely cause of the connectivity issue?

Accepted Answer

The RDS instance is in a private subnet and does not have a public IP address. Option C is correct because RDS instances are not accessible from the internet by default; they must be launched in a public subnet with a public IP. Option A is wrong because security groups are properly configured. Option B is wrong because network ACLs allow all traffic. Option D is wrong because port 1433 is the default SQL Server port.

Answer

The network ACL is blocking the traffic

Answer

The security group inbound rule is incorrectly configured

Answer

The database port is not 1433