How RCU's are calculated in DynamoDB Rightsizing Recommendations

Products

• CloudHealth

Issue/Introduction

Under Rightsizing > DynamoDB, we can see the RCUs and following article gives details on the calculation of RCUs in Rightsizing.

Resolution

The default Average Efficiency Target (ET) is based on 50%-75% target usage of provisioned RCU and WCU. The platform gives recommendation such that the actual usage should be of only 50-75% of provisioned. If full usage of provisioned capacity is desired, a custom Efficiency Target can be created with target usage as 99-100%.

RCU is a metric calculated per second, but our CloudWatch collection is per hour. The platform receives the metrics from CloudWatch per hour and then divide it by 3600 to get per second value. This is then used to get average and max values of metric usage, which then is used to give RCU and WCU recommendation based on target usage.

For example, if there are 30,000 million Read request in a given month, divide it to get per second value which is 30,000 million / (30*24*60*60) = which comes around 11k RCU (per second value). Furthermore, these recommendation are then given based on current month usage metrics and the Average RCU.