CPU Mismatch between Tagged Web Request and its purepaths
Hi,
Our team noticed recently that when we open Tagged Web Request (lets call it TWR) dashlet, and pick a specific TWR and drilldown to its purepaths, the CPU Sum of TWR may not exactly match the combined CPU Sum of all the purepaths it drilled down to. This is happening for some of the TWR and not all of them.
On the other hand, for each TWR we have, the CPU Sum always exactly matches combined CPU Sum of all its Web Requests, which is good.
Similarly, if we drill down from purepaths (selecting all purepaths) to "methods" dashlet, the combined CPU Sum of all the methods exactly match that of the purepaths. This is also good.
So, it is the mismatch between TWR and Purepaths CPU Sum">CPU Sum which is bothering us. Some of the differences are huge starting from 400 ms going up to 4 sec.
We could not find any specific reason for this.
Can someone please clarify?
Regards,
VM
Vaibhav,
The dashboard I sent you was indeed 6.2. My apologies! I'm pretty sure you can change the version just by editing the XML, but anyway I'll get you a 6.1 version shortly.
There are several master-slave dashboards in the client, including the Load Testing dashboard and the Web Request Performance dashboard. You get to the former from the Start Center, and the latter from the Web Request Performance link in the lower right of the monitoring "home page". The feature is not documented, but it is available for internal use.
The dashboard I sent you won't give you the numbers you want in the REST interface. If you want accurate numbers now, until the bug is fixed, I'd recommend you build your own PurePath business transaction splitting on the tags you want and build a new dashboard from that business transaction.
-- Graeme
Hi Graeme, Is there a defect Id which we could track to its implementation? Thanks.
Hi Graeme,
I created the blank PP business transaction as you said. However, I was not able to open the dashboard after saving it locally. It gives "Unable to open/load 'TWR workaround' from <location>" error. Could be due to DT version mismatch, as I am using 6.1.0.7880 and yours is 6.2.0.1239.
Also, the concept of slave pane in TWR dashboard is new to me. I don't see any such option in my DT client.
On the other hand, if I am able to make this new dashboard work, the problem I will face is to get this slave pane data pulled via REST interface for each and every TWR. Any thoughts?
Regards,
Vaibhav
Vaibhav,
I've built you a work-around dashboard, attached. You'll need to build a blank PurePath business transaction – one with no extra filter, result or splitting measures – called All PPs. Then you can open this dashboard, which is basically a copy of the Tagged Web Requests dashboard with a "slave" pane below it that shows the correct CPU data for whatever you click on in the upper pane.
Attachment: TWR workaround.dashboard.xml
You'll also need to switch the dashboard source.
Let me know if this helps!
-- Graeme
Glenn,
I expect they'll fix the calculation – there's no precedent for displaying the current value anywhere other than the PP tree.
The issue also applies to the ordinary Web Request dashboard, so you got a twofer!
-- Graeme
Thanks Graeme.
Yes, we noticed about WR dashboard also. In fact, it might be how DT consolidates and shows data at TWR level !
So, until this fix is available, we need to add CPU Sum of all Purepaths belonging to a WR/TWR to get a more correct measurement of CPU for that WR/TWR.
Is that correct?
-- Vaibhav
Thanks, Graeme. There's no urgency, now that we understand the issue. What exactly is the fix? Is it just labeling, or the calculation itself?
Glenn,
It's a bug. If you'd like a patch, you'll need to submit a support ticket.
Otherwise, you can wait for the fix to be rolled out in a regular release. If you post here in a week or so, I can probably let you know when.
-- Graeme
Ok, this is interesting. The PurePath contains 3 asynchronous threads, which are included in the Purepath's CPU Sum, but not in the Web Request's (or Tagged Web Request's) CPU Sum. This is great information...it explains the sporadic differences we have been seeing. Maybe the CPU Sum column for the Web Request and Tagged Web Request dashlets should be renamed to CPU Total?
Glenn,
The Tagged Web Request dashboard is taking the CPU sum value from the CPU total of the first thread. You can see what's going on in the PP dashboard:
This is correct – Dynatrace is pretty consistent is using "total" to mean "including children" and "sum" to mean "all threads". You can find the remainder of the PP CPU sum in the other threads lower down in the PP.
The question is, why is the Tagged Web Requests dashboard displaying the value for the first thread?
Could someone from R&D say whether this is a bug or works-as-designed, please?
-- Graeme
Glenn,
Is there any chance you can send us a PurePath so we can take a look at it?
If not, you might consider opening a support ticket.
-- Graeme
