Calculating rate of change in Log Analytics

[Peter Hall]

If I have a counter that increases over time and I want to display how much that counter is changing every minute, how would I do that.  In PromQL I would use the rate function but is there a simple equivalent KQL?

For example, 14:10:00 the total value since we collected data was 182077, at 14:11 it was 182083 and at 14:12 it was 182084.  I would like to render a graph showing 0 at 14:10, 6 at 14:11 and 1 at 14:12. 

Sounds simple but I can't see a way to do it.  Any help would be appreciated.

Regards

Pete

[#2]

@Peter Hall 

Have you looked at bin? https://docs.microsoft.com/en-us/azure/kusto/query/binfunction

Event
| where TimeGenerated > ago(1h)
| summarize count(EventID) by bin(TimeGenerated, 1m)

This shows the count of EventIDs in the Events table every min in the past hour?

Go to Log Analytics and Run Query

Adding as this as the last line will give you the graph, rather than a table.

| render barchart

[#3]

@CliveWatson Thanks for the reply.  I have looked at that.  It's not the number of new entries per minute I am trying to ascertain, but the change in the sum of all previous entries per minute, if that makes sense.  

ie in the above query, you'll see system mode cpu usage for computer aks-agentpool-31816283-2 goes from 264552.21 to 264560.83 in the minute, so i want the difference between those 2 on an on-going basis.  In fact, I actually want it for all modes but one step at a time.

[#4]

@Peter Hall 

How about?

Event
| where TimeGenerated > ago(1h)
| summarize count() by bin(TimeGenerated, 1m)
| sort by TimeGenerated asc 
| extend accumulated =row_cumsum(count_)

Go to Log Analytics and Run Query

TimeGenerated	count_	accumulated
2019-09-12T14:46:00Z	343	343
2019-09-12T14:47:00Z	57	400
2019-09-12T14:48:00Z	49	449
2019-09-12T14:49:00Z	488	937
2019-09-12T14:50:00Z	321	1258
2019-09-12T14:51:00Z	354	1612
2019-09-12T14:52:00Z	378	1990
2019-09-12T14:53:00Z	482	2472
2019-09-12T14:54:00Z	344	2816
2019-09-12T14:55:00Z	501	3317

[#5 · Accepted solution]

@CliveWatson you are a scholar and a gent.  That would appear to do the trick.  I'll adapt as necessary but thank you

[#6]

You can also use the next or prev functions to get the rate
https://docs.microsoft.com/en-us/azure/kusto/query/prevfunction

[#7]

@Ketan GhelaniThanks very much for the reply.  I'll take a look at that as well

[#8]

@Peter Hall Did you find out prometheus "rate" equivalent function in kusto

[#9]

@santhoshparepu For anyone still looking for a Prometheus equivalent to rate of change the link below defines a Kusto User Defined Function to calculate rate of change from a Prometheus style counter which can only go up, unless reset. series_rate_fl() - Azure Data Explorer | Microsoft Docs