Calculating rate of change in Log Analytics

Peter Hall
New Contributor

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.




6 Replies

@Peter Hall 


Have you looked at bin?

| 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




@Clive Watson 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.

@Peter Hall 


How about?

| 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



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

You can also use the next or prev functions to get the rate

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

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