DBS-C01 Monitoring and Troubleshooting Practice Test 10 — 15 Questions

Question 1

A company is running an Amazon Aurora MySQL-Compatible DB cluster. The application is experiencing increased latency during peak hours. The DB cluster's CPU utilization is at 40%, but the ReadReplicaLag metric is high. Which of the following is the most likely cause?

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

Accepted Answer

The writer instance is experiencing I/O bottlenecks, causing slow replication. In Aurora MySQL, high ReadReplicaLag with low CPU utilization on the writer typically indicates that the writer is experiencing I/O bottlenecks or is busy with writes that delay binlog propagation to replicas. Aurora replicas apply changes from the writer's log stream, so if the writer is slow to flush or generate log records, replicas fall behind. This manifests as increased read latency on replicas.

Answer

The read replica is receiving too many write requests

Answer

The DB cluster parameter group is misconfigured

Answer

The binary log retention period is too long

Question 2

A database administrator is troubleshooting a slow-running query on an Amazon RDS for MySQL DB instance. Which CloudWatch metric should be monitored to determine if the query is experiencing storage I/O bottlenecks?

Accepted Answer

ReadLatency and WriteLatency. ReadLatency and WriteLatency indicate I/O performance. Option B is wrong because CPUUtilization measures processor usage. Option C is wrong because NetworkThroughput measures network traffic. Option D is wrong because DatabaseConnections measures connections.

Answer

CPUUtilization

Answer

NetworkThroughput

Answer

DatabaseConnections

Question 3

A company uses Amazon RDS for MySQL with Multi-AZ deployment. The database experiences intermittent write latency spikes. CloudWatch shows elevated 'WriteLatency' and 'WriteIOPS' but normal 'CPUUtilization'. Which is the MOST likely cause?

Accepted Answer

The instance is exceeding the provisioned IOPS burst balance. Elevated WriteLatency and WriteIOPS with normal CPUUtilization points to a storage-layer bottleneck, not compute. RDS gp2/gp3 volumes have a burst balance (IOPS credits); when the baseline is exceeded for sustained periods, the volume throttles and write latency spikes. Multi-AZ synchronous replication is normal behavior and does not cause intermittent spikes with normal CPU.

Answer

A parameter group change was applied without rebooting

Answer

A read replica is being used for write operations

Answer

Multi-AZ replication is causing synchronous writes to the standby

Question 4

A DevOps engineer notices that an Amazon DynamoDB table's read capacity is frequently throttled during peak hours. The table has read-once, read-many workload. Which action is MOST cost-effective to reduce throttling?

Accepted Answer

Enable DynamoDB Accelerator (DAX). DynamoDB Accelerator (DAX) caches frequently read items, reducing the number of read requests to the table. For a read-once, read-many workload, this significantly lowers read capacity consumption, thus reducing throttling cost-effectively. Option A is incorrect: Enabling auto-scaling for read capacity would help reduce throttling by automatically adjusting capacity, but it does not reduce the number of reads; it increases capacity when needed, which can be more expensive than using DAX. Option C is incorrect: Switching to On-Demand capacity mode eliminates throttling by paying per request, but for a predictable, high-read workload, this is typically more expensive than provisioned capacity with DAX. Option D is incorrect: Increasing the provisioned read capacity units would reduce throttling, but it increases cost because you pay for higher capacity even during off-peak hours. DAX is more cost-effective as it reduces the required capacity.

Answer

Enable auto-scaling for read capacity

Answer

Switch to On-Demand capacity mode

Answer

Increase the provisioned read capacity units

Question 5

A database specialist is troubleshooting an Amazon Aurora MySQL cluster. The writer instance's CPU is at 90% and there are frequent 'Lock wait timeout exceeded' errors. The application uses many short-lived connections. What should the specialist do FIRST to reduce lock contention?

Accepted Answer

Enable RDS Proxy to pool database connections. Enabling RDS Proxy (C) pools and shares database connections, reducing the overhead of establishing new connections and alleviating lock contention caused by many short-lived connections. RDS Proxy maintains a pool of persistent connections to the database, allowing the application to reuse them, which reduces the number of concurrent sessions and thus lock waits. This directly addresses the root cause of the contention.

Answer

Add additional read replicas to distribute read traffic

Answer

Increase the instance size to handle more concurrent transactions

Answer

Reduce the maximum number of connections in the application

Question 6

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The migration uses AWS DMS. After the migration, the database has a 30-minute recovery point objective (RPO). Which Amazon RDS feature should be configured to meet a 5-minute RPO?

Accepted Answer

Enable automated backups with a retention period of 7 days. The correct option is C: enable automated backups with a retention period of 7 days. For Amazon RDS for Oracle, automated backups enable point-in-time recovery (PITR) by continuously archiving transaction logs to S3, allowing you to restore to any second within the retention window (up to 35 days), which supports an RPO of about 5 minutes. Multi-AZ (A) provides high availability through synchronous standby replication for failover, not a 5-minute RPO for point-in-time recovery. Manual snapshots every 5 minutes (B) are not automatic, incur overhead, and cannot achieve continuous PITR. A cross-region read replica (D) is for read scaling and disaster recovery, not for meeting a 5-minute RPO on the primary database.

Answer

Enable Multi-AZ deployment

Answer

Take manual snapshots every 5 minutes

Answer

Create a read replica in another region

Question 7

A developer reports that an Amazon ElastiCache for Redis cluster's memory usage is consistently above 90%. The application uses Redis for caching and session storage. Which configuration change would MOST effectively reduce memory pressure?

Accepted Answer

Enable eviction with volatile-LRU policy. Enabling an eviction policy such as volatile-LRU lets Redis reclaim memory by evicting keys that have a TTL set when maxmemory is reached, which directly reduces memory pressure without changing the node size. Since the workload mixes caching and session storage, volatile-LRU targets only expirable keys, preserving persistent session data that lacks a TTL.

Answer

Scale up to a larger node type

Answer

Enable AOF persistence to free memory

Answer

Disable replication to reduce memory overhead

Question 8

A database specialist is monitoring an Amazon DynamoDB global table with two replicas in separate regions. The specialist notices that the 'ReplicatedWriteConflictCount' metric is increasing. What is the MOST likely cause?

Accepted Answer

The same item is being written concurrently in multiple regions. Concurrent writes to the same item in different regions cause conflicts. Option A is wrong because provisioned throughput affects throttling, not conflicts. Option B is wrong because network latency does not cause conflicts. Option C is wrong because eventual consistency does not cause conflicts.

Answer

Insufficient write capacity in one of the regions

Answer

High network latency between the regions

Answer

The application is using strongly consistent reads

Question 9

A company uses Amazon RDS for PostgreSQL with logical replication to a downstream system. The replication slot grows unbounded and causes storage full issues. Which action resolves this without data loss?

Accepted Answer

Monitor the replication slot and advance it using pg_replication_slot_advance. A growing replication slot on RDS for PostgreSQL indicates the downstream consumer is not confirming WAL positions, so PostgreSQL retains WAL segments indefinitely. The correct remediation without data loss is to monitor the slot and use pg_replication_slot_advance to move the confirmed_flush_lsn forward past already-consumed WAL, releasing storage. This preserves the slot and avoids breaking replication while reclaiming space.

Answer

Disable logical replication and use DMS instead

Answer

Increase the allocated storage size of the RDS instance

Answer

Delete the replication slot and recreate it

Question 10

A company uses Amazon Redshift for data warehousing. A nightly ETL job fails with 'Disk full' error on some nodes. The cluster has 8 dc2.large nodes. Which action will MOST efficiently resolve the issue without increasing costs?

Accepted Answer

Run a VACUUM command to reclaim space. Running VACUUM reclaims disk space by sorting and re-sorting rows, removing deleted rows, and recovering space from unsorted or deleted data — directly addressing the 'Disk full' error without adding nodes or cost. It is the most efficient no-cost remediation for space reclamation on an existing Redshift cluster.

Answer

Increase the number of slices per node

Answer

Add more nodes to the cluster

Answer

Enable compression on all tables

Question 11

A company uses Amazon RDS for PostgreSQL with Multi-AZ. The primary instance fails and a failover occurs. After failover, the application reports elevated write latency. Which TWO are possible causes?

Accepted Answer

The buffer pool is not warm on the new primary. After a Multi-AZ failover, the new primary instance starts with a cold buffer pool (no cached data blocks). PostgreSQL relies on shared buffers to cache frequently accessed data; without a warm cache, every read request must fetch data from disk, which increases I/O and write latency because writes often require reading the affected pages first. This is a known behavior in RDS for PostgreSQL after failover, and it resolves as the buffer pool warms up over time.

Answer

A read replica is now promoting to primary

Answer

The new primary has a smaller instance size

Answer

Automated backups are running on the new primary

Question 12

A database administrator notices that an Amazon RDS for MySQL instance's storage is filling up unexpectedly. The administrator has enabled automated backups and retains them for 7 days. Which of the following actions would help reduce storage consumption without losing the ability to perform point-in-time recovery?

Accepted Answer

Reduce the backup retention period to 1 day. Reducing the backup retention period reduces the amount of storage consumed by automated backup data, while still allowing point-in-time recovery for the duration of the retention period. Option A is incorrect because changing the instance class does not affect storage consumption. Option C is incorrect because deleting manual snapshots does not reduce the automated backup storage that is likely causing the unexpected filling, and manual snapshots are not necessary for point-in-time recovery. Option D is incorrect because disabling automated backups eliminates point-in-time recovery capability.

Answer

Modify the DB instance to a smaller instance class

Answer

Delete manual DB snapshots

Answer

Disable automated backups

Question 13

A company is using Amazon Redshift for data warehousing. The operations team notices that queries are running slower than usual. Which Amazon Redshift system view should be used to identify the queries that are consuming the most resources?

Accepted Answer

STL_QUERY. STL_QUERY (option B) is the correct system view because it stores detailed information about query execution, including resource consumption. This allows the operations team to identify which queries are consuming the most resources. The other options are incorrect: SVV_VACUUM_PROGRESS (option A) shows the progress of vacuum operations, not query performance. PG_TABLE_DEF (option C) shows table definitions. STV_TBL_PERM (option D) shows table permissions, not query resource usage.

Answer

SVV_VACUUM_PROGRESS

Answer

PG_TABLE_DEF

Answer

STV_TBL_PERM

Question 14

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. The most effective action. Using 'Limited LOB mode' in AWS DMS reduces the overhead of replicating large objects by only transferring metadata until the LOB is accessed, and increasing the max LOB size ensures that LOBs fit within a single transaction, preventing fragmentation. Option A is incorrect because disabling Multi-AZ does not directly affect DMS replication performance; Multi-AZ provides high availability but does not impact replication throughput. Option B, increasing the Aurora instance size, may help if the instance is CPU or memory constrained, but the primary bottleneck in replication is often the handling of large objects, making DMS task configuration more targeted. Option C is incorrect because using a smaller instance would worsen performance, not improve it.

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 15

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. AWS Lambda can be configured with a DynamoDB Streams trigger to automatically invoke a Lambda function for each stream record. This is the native, serverless way to process stream records in real time without managing polling infrastructure.

Answer

Amazon Kinesis Data Firehose

Answer

Amazon Simple Queue Service (SQS)

Answer

AWS Step Functions