Forum Discussion
Resolver IWhy is there CU usage while no activity running?
Community ChampionSQL queries are counted as background queries and are smoothed for 24 hours. https://learn.microsoft.com/en-us/fabric/enterprise/fabric-operations#data-warehouse
"the cumulative smoothing is about 10 times the cost of the initial activity." Can you describe how you found this number?
"add to that activities coming from nowhere, like a lakehouse not used for the past weeks start consuming CUs for no reason." What kind of transactions are you being billed for? Is it OneLake read transactions? This can be found in the Items (14 days) visual. Is the Lakehouse being queried? E.g. are some Power BI reports using the Lakehouse data, or some other processes using the Lakehouse data?
"I did extensive analysis of these background operations.
they starts as soon as I pause and resume my instance, before conducting any type of activity." What kind of operations are these? Is it SQL queries, dataflow gen2, spark notebook, pipeline, etc.?
"like currently I have 0.625CU consumed by a process terminated yesterday (a pipeline), the dataflow consumed 1800CU, paid yesterday." Background operations are smoothed for 24 hours after they finish. It's normal that operations from yesterday are still showing in the Timepoint page.
"and a consumption during this time greater than the activity itself." Can you describe what you mean by greater than the activity itself? How do you know the consumption of the activity itself? And where do you see that you are smoothed for more consumption than the activity itself?
Resolver II sent a example:
I have 0.625CU consumed for 24h, related to a pipeline which consumed 1800CU.
so this background activity will cost me 54 000CU per 24h for something which cost only 1800CU during its execution and was burndown in seconds.
0.625 * 60 * 60 * 24 = 54 000 CU in total
if the impact on my capacity is 0.625, this activity should consumed my capacity for 48 minutes
0.625 * 60 * 48 = 1800
else I expect, 1800 / (24 * 60 * 60) = 0.0208 CU consumed for 24h
for my lakehouse, yes, I had activities 10 days ago, nothing after that.
it's just an example, I'm seeing activities poping from everywhere.
remember: I'm reaching 200 000 + background activities!!!
just by running few pipelines a day, nothing complicated. and the number of user is pretty low for now (mainly myself and few people running 5 reports in the day)
- frithjof_v
On my trial capacity (I am the only user), I have 75 000 background activities being smoothed at the moment. It doesn't mean any of these background activities are running now. This is the number of background activities which ended during the last 24 hours.
These 75 000 background activities are costing me 10% of my trial capacity.
"I have 0.625CU consumed for 24h, related to a pipeline which consumed 1800CU.
so this background activity will cost me 54 000CU per 24h for something which cost only 1800CU during its execution and was burndown in seconds."
I am guessing the Total CU (s) is 1800CU.
0.625 CU (s) / 30 s * 60 s/min * 60 min/h * 24 h = 1800CU (s).
So I am guessing you will pay in total 1800CU (s).
I think this makes sense.
The Total CU (s) is the cost of the operation. I don't think you will pay 54000CU. I think you will pay 1800CU (s). What makes you think 54000CU is the amount you will pay?
I think these two visuals (red boxes) are the ones which provide the most useful information. Here we can find the actual resource usage, and what day and what hour the usage really happened. Yes, it will be billed over a 24 hour period after the usage actually happened. But these two visuals show when the usage actually happened, which I prefer.