DBS-C01 Practice Exam 68 — 20 Questions

Question 1

A company uses Amazon DynamoDB with a table that has a partition key of 'user_id' (string) and sort key of 'timestamp' (number). The application queries for recent items for a specific user using the query API with KeyConditionExpression. The query returns items in descending order. Occasionally, the query returns items that are not the most recent. What is the most likely cause?

Accepted Answer

The query is using eventually consistent reads, which may not reflect the latest writes.. DynamoDB stores items with the same partition key in sorted order by sort key. Queries return items in order by default. Option C is correct because if the application uses eventually consistent reads, the data might be stale. Option A is wrong because GSIs don't affect base table queries. Option B is wrong because the query returns items in order, but eventually consistent reads may not reflect latest writes. Option D is wrong because pagination is not the cause.

Answer

The query is not using the ScanIndexForward parameter set to false.

Answer

The query results are paginated and the application is not iterating through all pages.

Answer

The query is using a global secondary index (GSI) that has a different sort key.

Question 2

A company is running an Amazon Aurora MySQL database cluster. The database specialist notices that the write latency is high during peak hours. The cluster consists of one writer and two reader instances. Which action should the specialist take to reduce write latency?

Accepted Answer

Increase the instance class of the writer instance to a larger size.. Option C is correct because increasing the instance class of the writer can improve performance. Option A is wrong because read replicas do not help with write latency. Option B is wrong because Auto Scaling does not apply to Aurora instance classes automatically. Option D is wrong because Multi-AZ is already inherent in Aurora.

Answer

Enable Auto Scaling on the cluster to automatically adjust capacity.

Answer

Enable Multi-AZ deployment for the cluster.

Answer

Add more reader instances to distribute the read load.

Question 3

A company is using Amazon Redshift for data warehousing. The VACUUM operation is taking longer than expected, and the database administrator wants to identify the tables that require the most vacuuming effort. Which system table should be queried to find the percentage of deleted rows per table?

Accepted Answer

SVV_TABLE_INFO. Option A is correct because SVV_TABLE_INFO contains the unsorted and tombstone information needed. Option B is wrong because STL_QUERY contains query logs. Option C is wrong because STV_TBL_PERM contains permanent table information but not vacuum metrics. Option D is wrong because PG_TABLE_DEF contains table definitions.

Answer

STL_QUERY

Answer

STV_TBL_PERM

Answer

PG_TABLE_DEF

Question 4

Refer to the exhibit. A developer is trying to query the ProductCatalog table using the 'Id' attribute. The query returns no results even though the developer knows data was inserted. What is the MOST likely cause?

Accepted Answer

The table contains no items. Option D is correct because the table has no items (ItemCount: 0). Option A is wrong because the table is active. Option B is wrong because provisioned throughput is not exceeded (ItemCount is 0). Option C is wrong because the attribute definition exists.

Answer

The provisioned throughput is exceeded

Answer

The attribute definition is missing the 'Id' attribute

Answer

The table is not in ACTIVE status

Question 5

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 6

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 7

A company's Amazon Redshift cluster is experiencing slow query performance. Which THREE diagnostic steps should be taken to identify the bottleneck?

Accepted Answer

Query SVL_QUERY_REPORT to see step-level performance. Option A is correct because STL_QUERY provides query execution details. Option C is correct because SVL_QUERY_REPORT shows step-level execution. Option E is correct because STL_WLM_QUERY shows WLM queue waits. Option B is wrong because STV_BLOCKLIST shows disk allocation, not performance. Option D is wrong because STL_LOAD_ERRORS is for load errors.

Answer

Query STL_LOAD_ERRORS to check for data load errors

Answer

Query STV_BLOCKLIST to check disk allocation

Question 8

A company is troubleshooting an Amazon RDS for MySQL DB instance that is experiencing high CPU utilization. The DB instance is a db.t3.medium. Which TWO actions should the database administrator take to investigate the cause?

Accepted Answer

Enable Performance Insights to identify the top SQL queries consuming CPU.. Option A is correct because enabling Performance Insights helps identify top SQL queries. Option B is correct because reviewing slow query logs helps identify inefficient queries. Option C is wrong because increasing instance size is a fix, not investigation. Option D is wrong because disabling Multi-AZ reduces availability, not CPU. Option E is wrong because modifying parameter groups without analysis is not investigative.

Answer

Disable Multi-AZ to reduce overhead.

Answer

Modify the DB parameter group to increase the query cache size.

Answer

Increase the DB instance class to a larger size.

Question 9

A company is using Amazon DynamoDB with global tables. The application team reports that data written in one region is not immediately available in another region. The database specialist needs to monitor the replication lag. Which CloudWatch metric should be used?

Accepted Answer

Monitor the 'ReplicationLatency' metric in the replica region.. Option B is correct because 'ReplicationLatency' measures the time taken for updates to propagate. Option A is wrong because 'ThrottledRequests' is for throttling. Option C is wrong because 'PendingReplicationCount' shows number of pending items, not time. Option D is wrong because 'ConsumedWriteCapacityUnits' is for capacity.

Answer

Monitor the 'ConsumedWriteCapacityUnits' metric in both regions.

Answer

Monitor the 'PendingReplicationCount' metric in the source region.

Answer

Monitor the 'ThrottledRequests' metric in the source region.

Question 10

A developer is troubleshooting an issue where an application using Amazon DynamoDB is receiving occasional 'ThrottlingException' errors. The application uses eventually consistent reads. What is the MOST likely cause of this error?

Accepted Answer

The read capacity units are set too low for the current traffic pattern. Option B is correct because ThrottlingException occurs when the request rate exceeds the provisioned throughput capacity. Option A is wrong because eventually consistent reads consume half the read capacity units, so they are less likely to cause throttling. Option C is wrong because network issues would cause timeout errors, not throttling. Option D is wrong because incorrect table name would cause ResourceNotFoundException.

Answer

The application is using an incorrect table name

Answer

The application is using eventually consistent reads instead of strongly consistent reads

Answer

There is a network connectivity issue between the application and DynamoDB

Question 11

A company is running a production Amazon RDS for MySQL DB instance. The application team reports intermittent connection timeouts. The DBA notices that the DB instance's CPU utilization spikes to 100% during these times. Which metric should be monitored to determine if the issue is due to a specific query?

Accepted Answer

Queries (engine-specific counter). Option D is correct because the RDS for MySQL engine-specific counter 'Queries' reflects the number of queries executed. Option A is wrong because DatabaseConnections shows connections, not query performance. Option B is wrong because ReadIOPS measures disk I/O, not query volume. Option C is wrong because NetworkThroughput measures network traffic.

Answer

DatabaseConnections

Answer

NetworkThroughput

Answer

ReadIOPS

Question 12

Which THREE steps should be taken to troubleshoot high replica lag in an Amazon Aurora MySQL DB cluster? (Choose THREE.)

Accepted Answer

Review network latency between the writer and replica. Options B, D, and E are correct. Checking the replica's load (B), examining replication threads (D), and reviewing network latency (E) are common troubleshooting steps. Option A (increasing instance size) is a solution, not a troubleshooting step. Option C (disabling binary logging) would break replication.

Answer

Increase the instance size of the replica

Answer

Disable binary logging on the writer

Question 13

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. Option B is correct because VACUUM reclaims space from deleted rows without adding cost. Option A is wrong because adding nodes increases cost. Option C is wrong because increasing slice count is not possible without changing node type. Option D is wrong because compression reduces storage but may not immediately free space.

Answer

Increase the number of slices per node

Answer

Add more nodes to the cluster

Answer

Enable compression on all tables

Question 14

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 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

Question 16

A developer reports that an application is unable to connect to an Amazon RDS for MySQL DB instance. The security group for the DB instance allows inbound traffic on port 3306 from the application server's security group. The DB instance is in a VPC with both public and private subnets. The application server is in a private subnet. What is the most likely cause of the connection failure?

Accepted Answer

The security group for the DB instance does not allow inbound traffic from the application server's security group.. If the DB instance is in a public subnet and the application server is in a private subnet, they are in different subnets within the same VPC, so they can communicate via private IPs if routing is correct. However, the most common issue is that the security group rule is not correctly associated or the DB instance is in a public subnet with a public DNS name that resolves to a public IP, but the private subnet cannot reach the internet. But the question implies the DB instance is in a public subnet; private subnet instances can reach public subnet instances via the VPC router. However, often the misconfiguration is that the DB instance's security group does not allow traffic from the application server's security group. Option D is correct because the security group rule might be missing or incorrect. Option A is wrong because NACLs are stateless and typically allow all outbound. Option B is wrong because the DB instance is in a public subnet, but the application server is in a private subnet, they can communicate within the VPC. Option C is wrong because the DB subnet group is for Multi-AZ, not single instance.

Answer

The DB instance is in a public subnet and the application server is in a private subnet, so they cannot communicate.

Answer

The network ACL for the private subnet is blocking outbound traffic to the DB instance.

Answer

The DB instance is not part of a DB subnet group that includes the private subnet.

Question 17

A database administrator is monitoring an Amazon RDS for PostgreSQL DB instance. The administrator notices that the DB instance is using more memory than expected. Which TWO metrics in Amazon CloudWatch can help diagnose memory usage?

Accepted Answer

FreeableMemory. Option A is correct because FreeableMemory shows available memory. Option D is correct because SwapUsage indicates swapping, which occurs when memory is low. Option B is wrong because ReadIOPS is I/O metric. Option C is wrong because DatabaseConnections shows connections, not memory. Option E is wrong because NetworkReceiveThroughput is network metric.

Answer

NetworkReceiveThroughput

Answer

ReadIOPS

Answer

DatabaseConnections

Question 18

A database specialist is monitoring an Amazon RDS for MySQL instance and notices that the 'CPUUtilization' metric is consistently above 90%. Which TWO actions should the specialist take to investigate the issue? (Select TWO.)

Accepted Answer

Use Performance Insights to identify the queries that are consuming the most CPU.. Option A is correct because Performance Insights can identify high-load queries. Option B is correct because Enhanced Monitoring provides OS-level metrics like CPU, memory, and disk I/O. Option C is wrong because increasing instance class is a solution, not an investigation step. Option D is wrong because enabling Multi-AZ does not help investigate CPU usage. Option E is wrong because disabling query cache is not a diagnostic action.

Answer

Disable the MySQL query cache to free up CPU.

Answer

Increase the instance class to provide more CPU resources.

Answer

Enable Multi-AZ to distribute the load to a standby instance.

Question 19

A company is using Amazon Aurora MySQL. The database performance has degraded, and the DBA wants to identify the queries that are waiting for locks. Which system table should be queried to find information about locking conflicts?

Accepted Answer

information_schema.INNODB_LOCKS. Option C is correct because INNODB_LOCKS shows current locks and InnoDB lock conflicts. Option A is wrong because PERFORMANCE_SCHEMA provides performance data but not specifically locks. Option B is wrong because INFORMATION_SCHEMA.PROCESSLIST shows current processes but not lock details. Option D is wrong because INFORMATION_SCHEMA.TABLES shows table metadata.

Answer

information_schema.TABLES

Answer

information_schema.PROCESSLIST

Answer

performance_schema.events_waits_current

Question 20

A developer notices that an Amazon RDS for PostgreSQL DB instance is running low on free storage space. The instance has 100 GB of allocated storage. What is the recommended first step to troubleshoot this issue?

Accepted Answer

Check for unused indexes or table bloat using pg_repack or similar tools. Option B is correct because checking for unused indexes or bloat is a typical starting point for storage issues. Option A is wrong because modifying storage is a solution, not a troubleshooting step. Option C is wrong because deleting logs may not recover much space. Option D is wrong because enabling auto scaling is a preventive measure, not a troubleshooting step.

Answer

Enable storage auto scaling

Answer

Modify the DB instance to increase allocated storage

Answer

Delete the oldest transaction logs