How to get the total number of provisioned read capacity units of a table in a month?

I'm trying to get the total number of provisioned of read capacity units of a DynamoDB table to calculate the cost of that table in a month, using CloudWatch metrics. This table has been switched from Provisioned to On-Demand, all of its metric statistics has been reset, so I don't know how many RCU has been used when it was in Provisioned mode. I'm also not allowed to manage tags used for calculating cost, so Cost Explorer is pretty much a "no go".

The target utilization of both RCU and WCU for all tables in the region is 50%.

My cli command is something like below:

aws cloudwatch get-metric-statistics \
    --namespace "AWS/DynamoDB" \
    --metric-name "ProvisionedReadCapacityUnits" \
    --dimensions Name=TableName,Value=my_table \
    --start-time 2024-04-01T00:00:00Z \
    --end-time 2024-04-30T23:59:59Z \
    --period 3600 --statistics Sum \
    --query "Datapoints[:].Sum"

// Result:
// [
//     120.0,
//     120.0,
//     125.0,
//     100.0,
//     ...
// ]

However, after getting the command result and adding them all up, the total number I got for this one table was way higher (almost 10 times) than the number of PRCU used for all tables in the region in that month, which is written in the billing report.

How can I get the precise total number of used capacity units of one table in one month, that matches the billing report?

If not, how can I get the cost of one specific table back in that time ?

Solution

Provisioned capacity should not use period SUM as you're adding up capacity that's provisioned. For example if I had 10 RCU provisioned and I looked at it for a 1 hour time frame with a period of 5 minutes, that would equate to 12*10=60 RCU, but I didn't use 60, I never went over 10.

Sun is not a valid statistic which is defined in the docs

Valid Statistics:

Minimum – The lowest setting for provisioned read capacity. If you use UpdateTable to increase read capacity, this metric shows the lowest value of provisioned ReadCapacityUnits during this time period.

Maximum – The highest setting for provisioned read capacity. If you use UpdateTable to decrease read capacity, this metric shows the highest value of provisioned ReadCapacityUnits during this time period.

Average – The average provisioned read capacity. The ProvisionedReadCapacityUnits metric is published at five-minute intervals. Therefore, if you rapidly adjust the provisioned read capacity units, this statistic might not reflect the true average