DBS-C01 Monitoring and Troubleshooting Practice Test 19 — 15 Questions

Question 1

A company is running a MongoDB-compatible Amazon DocumentDB cluster. The application team reports that write operations are failing intermittently with a `WriteConcernError` indicating that the write concern could not be satisfied. The cluster has one primary and two replicas. What is the MOST likely cause of this issue?

Accepted Answer

One of the replicas is down or experiencing high replication lag. Option D is correct because if the write concern is set to 'majority' and a replica is down or lagging, the write cannot be acknowledged. Option A is wrong because the primary is not overloaded; the issue is write concern. Option B is wrong because read preference does not affect writes. Option C is wrong because the number of replicas is sufficient for majority if all are healthy.

Answer

The cluster does not have enough replica instances to satisfy the write concern

Answer

The application is using an incorrect read preference

Answer

The primary instance is overloaded with read requests

Question 2

A company is migrating an on-premises Oracle database to Amazon Aurora PostgreSQL. The migration uses AWS Database Migration Service (DMS) with ongoing replication. The team notices that the target Aurora database is falling behind the source during peak hours. Which of the following actions would MOST effectively improve the replication performance?

Accepted Answer

Configure the DMS task to use 'Limited LOB mode' and increase the max LOB size. Option B is correct because increasing the DMS task's max LOB size or setting LOB mode to 'Limited' can reduce overhead when replicating large objects. Option A is wrong because increasing Aurora instance size may help but DMS task configuration is more direct. Option C is wrong because disabling Multi-AZ does not affect DMS performance. Option D is wrong because using a smaller Aurora instance would worsen performance.

Answer

Disable Multi-AZ on the target Aurora cluster

Answer

Increase the Amazon Aurora instance size

Answer

Use a smaller Aurora instance to reduce write latency

Question 3

A company is using Amazon ElastiCache for Redis as a caching layer. The application is experiencing higher latency than expected. The team suspects that cache evictions are occurring due to memory pressure. Which ElastiCache metric should be monitored to confirm this?

Accepted Answer

Evictions. Option D is correct because `Evictions` metric shows the number of evicted keys due to memory limit. Option A is wrong because `CacheHits` shows successful reads. Option B is wrong because `CurrConnections` shows current connections. Option C is wrong because `ReplicationLag` shows replication delay, not evictions.

Answer

CurrConnections

Answer

ReplicationLag

Answer

CacheHits

Question 4

A company is using Amazon DynamoDB and has enabled DynamoDB Streams. The application needs to process stream records in real-time. Which AWS service can be used to invoke a Lambda function automatically for each stream record?

Accepted Answer

AWS Lambda. Option B is correct because Lambda can be triggered directly from DynamoDB Streams. Option A is wrong because Kinesis Data Firehose is for loading streaming data into destinations, not for triggering Lambda. Option C is wrong because SQS is for message queuing, not directly from DynamoDB Streams. Option D is wrong because Step Functions coordinates workflows, but does not directly trigger from DynamoDB Streams without Lambda.

Answer

Amazon Kinesis Data Firehose

Answer

Amazon Simple Queue Service (SQS)

Answer

AWS Step Functions

Question 5

A company is running an Amazon RDS for SQL Server instance with Multi-AZ deployment. The database is used by a critical application. During a recent failover test, the application experienced a 2-minute downtime. The application's connection string uses the DB instance endpoint, not the cluster endpoint. Which change would minimize downtime during future failovers?

Accepted Answer

Modify the application to use the cluster endpoint instead of the instance endpoint. Option D is correct because using the cluster endpoint (CNAME) automatically redirects to the current primary, reducing downtime. Option A is wrong because enabling Multi-AZ is already done. Option B is wrong because increasing instance size does not reduce failover time. Option C is wrong because read replicas are for read scaling, not failover.

Answer

Increase the DB instance class size

Answer

Create a read replica in a different Availability Zone

Answer

Enable Multi-AZ on the DB instance

Question 6

A company is using Amazon RDS for MySQL and needs to monitor for slow queries. Which TWO AWS services can be used to capture and analyze slow query logs? (Choose TWO.)

Accepted Answer

Amazon RDS Performance Insights. Options A and C are correct because CloudWatch Logs can be used to stream RDS logs, and Performance Insights can help identify slow queries. Option B is wrong because CloudTrail records API calls, not database logs. Option D is wrong because S3 is a storage service, not a monitoring service. Option E is wrong because Config records configuration changes.

Answer

Amazon S3

Answer

AWS Config

Answer

AWS CloudTrail

Question 7

A company is using Amazon DynamoDB with auto scaling enabled. Despite auto scaling, the application is still experiencing throttling during traffic spikes. Which THREE actions should the company take to resolve this issue? (Choose THREE.)

Accepted Answer

Implement exponential backoff in the application code. Options A, D, and E are correct. Enabling DynamoDB Accelerator (DAX) reduces read load. Implementing exponential backoff helps retry gracefully. Using DynamoDB global tables can distribute write load. Option B is wrong because disabling auto scaling would not help. Option C is wrong because switching to on-demand capacity might help but is not always cost-effective and does not address hot keys.

Answer

Switch to on-demand capacity mode

Answer

Disable auto scaling and set fixed capacity

Question 8

A company is using Amazon Redshift and notices that queries are running slowly. Which TWO system views should be used to identify the cause of the slow queries? (Choose TWO.)

Accepted Answer

STL_QUERY. Options A and C are correct. STL_QUERY contains query execution details. SVV_QUERY_STATE shows currently running queries. Option B is wrong because STV_TBL_PERM shows permissions. Option D is wrong because PG_TABLE_DEF shows table definitions. Option E is wrong because STL_LOAD_COMMITS shows load commit information.

Answer

STV_TBL_PERM

Answer

PG_TABLE_DEF

Answer

STL_LOAD_COMMITS

Question 9

A company runs an e-commerce platform on AWS using a multi-tier architecture. The application tier consists of Auto Scaling groups of EC2 instances behind an Application Load Balancer. The database tier uses Amazon RDS for MySQL with Multi-AZ deployment. Recently, the operations team noticed that during flash sales, the application becomes unresponsive and users receive 503 errors. The team checks CloudWatch metrics and sees that the RDS instance's CPU utilization spikes to 100%, and the `DatabaseConnections` metric also spikes to the maximum allowed value of 500. The application uses connection pooling with a maximum of 200 connections, but the metric shows 500 connections. The team suspects that the connection pooling configuration is not being honored. The application code is written in Python and uses SQLAlchemy with a connection pool size of 10 per application instance. There are 20 application instances in the Auto Scaling group during peak times. The team wants to resolve the issue without increasing the database instance size. What should the team do?

Accepted Answer

Set the `max_connections` parameter in the RDS parameter group to 200 and configure the application to handle connection errors with retry logic. Option B is correct because setting a maximum number of connections in the RDS parameter group enforces a hard limit, preventing the database from accepting more connections than the application can handle, which will cause connection errors that the application can handle gracefully. Option A is wrong because increasing the connection pool size per instance would increase the total connections, worsening the problem. Option C is wrong because reducing the number of application instances may reduce load but is not a scalable solution and doesn't address the root cause of connection limit. Option D is wrong because switching to Aurora may help but is a larger change and does not fix the connection management issue directly.

Answer

Reduce the Auto Scaling group's desired capacity to 10 instances during flash sales

Answer

Migrate the database to Amazon Aurora MySQL with Auto Scaling enabled

Answer

Increase the SQLAlchemy pool size to 25 per instance to reduce connection contention

Question 10

A database administrator notices that the CPU utilization on an Amazon RDS for PostgreSQL instance is consistently above 90% during peak hours. Which CloudWatch metric should be checked first to identify the cause of the high CPU usage?

Accepted Answer

DatabaseConnections. Option A is correct because DatabaseConnections can indicate high concurrent sessions causing CPU spikes. Option B is wrong because ReadIOPS may not directly cause CPU. Option C is wrong because SwapUsage is memory-related. Option D is wrong because NetworkThroughput is network-related.

Answer

NetworkThroughput

Answer

SwapUsage

Answer

ReadIOPS

Question 11

A company is running a production Amazon Aurora MySQL database. The database performance has degraded over the past week. The DBA suspects an increase in lock waits. Which tool should be used to identify queries experiencing lock waits?

Accepted Answer

Amazon RDS Performance Insights. Option B is correct because Performance Insights shows wait events and SQL queries. Option A is wrong because CloudWatch Logs doesn't show lock waits directly. Option C is wrong because Enhanced Monitoring shows OS metrics. Option D is wrong because AWS Trusted Advisor is for best practices.

Answer

Amazon CloudWatch Logs

Answer

Amazon RDS Enhanced Monitoring

Answer

AWS Trusted Advisor

Question 12

A company is using Amazon DynamoDB with auto scaling. The application is experiencing increased read latency. The monitoring shows that the ReadThrottleEvents metric is high. Which action should the company take to reduce read throttling?

Accepted Answer

Implement DynamoDB Accelerator (DAX) for caching.. Option C is correct because DynamoDB Accelerator (DAX) reduces read latency and throttling by caching. Option A is wrong because increasing write capacity doesn't help reads. Option B is wrong because enabling Streams may add overhead. Option D is wrong because switching to on-demand may increase cost but not necessarily fix throttling if workload is bursty.

Answer

Switch the table to on-demand capacity mode.

Answer

Enable DynamoDB Streams on the table.

Answer

Increase the write capacity units.

Question 13

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 14

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 15

A company is experiencing slow query performance on an Amazon RDS for MySQL database. The DBA wants to identify the most time-consuming queries. Which TWO actions should the DBA take? (Choose two.)

Accepted Answer

Use Amazon RDS Performance Insights.. Amazon RDS Performance Insights (Option D) provides a database performance tuning and monitoring feature that visualizes database load and identifies the most time-consuming queries by breaking down wait events, SQL statements, and hosts. It directly helps the DBA pinpoint the specific queries causing performance degradation without additional configuration or overhead.

Answer

Enable the audit log.

Answer

Enable the general log and review it.

Answer

Use Amazon RDS Enhanced Monitoring.