DynamoDB: ReturnConsumedCapacity does not return RCU or WCUs

Question

When writing to DynamoDB or reading from DynamoDB you can specify: ReturnConsumedCapacity.

When you do this the API does return total CapacityUnits, but I am not able to get it to return ReadCapacityUnits or WriteCapacityUnits. The documentation indicates we should indeed get data on RCUs and WCUs: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_ConsumedCapacity.html

This is true whether or not you set ReturnConsumedCapacity to TOTAL or INDEXES.

This is also true if you are simply doing a read query too.

Is there anyway to get RCUs and WCUs returned?

Here is a sample query:

aws.exe dynamodb query \
    --table-name tableName \
    --index-name GSI1 \
    --key-condition-expression "GSI1PK = :pk" \
    --expression-attribute-value '{":pk": {"S": "blah"}}' \
    --return-consumed-capacity TOTAL

which returns something like this:

    "ConsumedCapacity": {
        "TableName": "tableName",
        "CapacityUnits": 128.5
    }

If I change the request from TOTAL to INDEXES I get:

    "ConsumedCapacity": {
        "TableName": "oaas-performance-table-dev",
        "CapacityUnits": 128.5,
        "Table": {
            "CapacityUnits": 128.5
        }
    }
}

pretty much the same in other words. No RCU or WCU.

Any idea how to get this additional data?

Answer 1

This is the intended behavior, per the Query docs:

TOTAL - The response includes only the aggregate ConsumedCapacity for the operation.

A query can only consume read capacity, so CapacityUnits is effectively the same thing as ReadCapacityUnits, and WriteCapacityUnits is always 0.