I was recently working with a customer and one of the questions they had is we are going to be running an ingestion process. We want to know how much Fabric Capacity this will be consuming.

The challenge with this question is that in Fabric a background capacity gets smoothed over 24 hours.

For example, when looking at the Capacity Metrics App I can see my overall usage, but HOW MUCH CAPACITY IS IT CONSUMING?

How do Background Capacity Units get calculated

Here is an example below how it works:

  • I run for example a notebook and the notebook consume 24 Capacity Units.
  • The notebook then finishes.
  • What then happens is that with Microsoft Fabric it will then allocate 1 Capacity Unit to Background utilization for the next 24 hours.
  • The way the calculation works is that it takes the amount of Capacity Units at the end of the process and divides it equally over the next 24 hours (This is known as smoothing).
  • EG: 24 Capacity Units / 24 hours = 1 Capacity Unit per hour

How did I calculate the Background utilization percentage

In my working example I am looking to understand how much of my capacity the Kusto Event House is consuming.

As shown above it uses about 353,000 Capacity Units per day.

To calculate the percentage usage, I did the following:

  • The first thing is what is the size of my Capacity.
    • In my example this is an F64
  • Next, I need to calculate how many Capacity Units that is per day
    • To calculate this, I take the size of my capacity which is an F64, which means 64 capacity Units and multiply it by the number of seconds in day which is 86400
    • 64 * 86,400 = 5,529,600
  • To calculate the amount of Capacity Units I get per hour is then 5,529,600 / 24 Hours
    • 5,529,600 / 24 = 230,400
  • I then need to calculate how many Capacity Units my Kusto event would consume in the next 24 hours.
    • 353,000 / 24 = 14,708
  • Finally, I can then calculate how much of my F64 Capacity will be consuming this process.
    • 14,708 / 230,400 = 6.38%

The overall calculation is the following below

(353,000 / 24 ) / ((64 * 86,400) / 24)

Summary

I hope you have found this useful. If you want an easy way to do this you can use my Excel file, in which you can put in your Fabric Capacity Size and the Total CUs Used

Any comments or suggestions is most welcome 😊