DBS-C01 Workload-Specific Database Design Practice Question
Exhibit
Refer to the exhibit.
CloudFormation snippet:
"OrdersTable": {
"Type": "AWS::DynamoDB::Table",
"Properties": {
"TableName": "Orders",
"AttributeDefinitions": [
{"AttributeName": "OrderID", "AttributeType": "S"},
{"AttributeName": "CustomerID", "AttributeType": "S"}
],
"KeySchema": [
{"AttributeName": "OrderID", "KeyType": "HASH"}
],
"GlobalSecondaryIndexes": [
{
"IndexName": "CustomerIndex",
"KeySchema": [
{"AttributeName": "CustomerID", "KeyType": "HASH"}
],
"Projection": {
"ProjectionType": "ALL"
},
"ProvisionedThroughput": {
"ReadCapacityUnits": 5,
"WriteCapacityUnits": 5
}
}
],
"ProvisionedThroughput": {
"ReadCapacityUnits": 5,
"WriteCapacityUnits": 5
}
}
}A developer is designing a DynamoDB table for an order management system using the above CloudFormation template. The application needs to query orders by CustomerID. The current design has a GSI on CustomerID. However, the developer notices that the GSI has low write throughput and often throttles. What is the most cost-effective way to improve write throughput on the GSI?
⚠ Common exam trap
The trap here is that candidates mistakenly believe that increasing the base table's write capacity will automatically increase the GSI's write throughput, but DynamoDB treats GSI capacity as a separate resource that must be provisioned independently.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the WriteCapacityUnits of the GSI from 5 to a higher value.
The GSI's write throughput is independent of the base table's write capacity. Increasing the GSI's WriteCapacityUnits directly addresses the throttling on the GSI without affecting the base table's cost or performance. This is the most cost-effective approach because it only scales the specific resource that is throttling, rather than over-provisioning the entire table or adding unnecessary infrastructure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the ProjectionType of the GSI to KEYS_ONLY.
Why it's wrong here
Projection type does not affect write throughput.
- ✗
Use Amazon SQS to buffer writes to the table.
Why it's wrong here
SQS does not affect DynamoDB write capacity.
- ✗
Increase the WriteCapacityUnits of the table.
Why it's wrong here
Table capacity does not affect GSI capacity.
- ✓
Increase the WriteCapacityUnits of the GSI from 5 to a higher value.
Why this is correct
GSI has its own provisioned throughput; increasing it alleviates throttling.
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