"2 items dropped from union(s)" after updating to v10.2

[maxemillion]

Hello,

I am using Grafana to display performance data from a few IBM i systems (formerly known as AS/400).
The data itself comes from Prometheus.

One of the things I display is the current load of active jobs in the system in %.
You can only have so much processes in the system before it shuts down.

I calculate this by using the following formula:

(Current Active Jobs * 100) / Maximum Possible Jobs

The actuall Math expression I use is this:

($CURJOBS * 100) / $MAXJOBS

I had Grafana v10.1.5 and updated to version Grafana v10.2.3.

After updating, I suddenly get the following error message for this calculation:

I have found this StackOverflow post, but don’t quite understand it.

I also don’t understand the error message itself, because the panel still gets displayed correctly:

This error seems to get thrown as soon as I use more than one variable.
This does not throw an error:

$CURJOBS + 100

This does throw an error:

$CURJOBS + $MAXJOBS

Both get displayed correctly.

Please help me solve this.

[jangaraj]

It is just warning (probably that warning was not implemented in older Grafana version). I guess your timestamps are not aligned, so it warns you:

Addition of queries via Expression option not working

What’s looks like a simple math (A+B) is not so simple. Start simple math: 10 (result from query A) + 10 (result from query B) = 20 (expected result from math expression $A+$B) Actually, result from query is timeseries (see query config Format as: Time series) - there is list of values and each value represent some value in time, so it can be: 10 (result from query A at 2024-01-01 00:00:00) + 10 (result from query B at 2024-01-01 00:00:00) = 20 (expected result from math expression $A+…

[maxemillion]

Hey, thanks for your input!

The thing is that I can’t seem to turn the warning off, nor do I have any idea how to resolve it.
The exclamation-mark-sign gets plastered all over my dashboard, which looks bad.

The calculation works and displays correct data - I have no use for this warning, it’s not even clear what it’s supposed to mean.

Googling the error message yields very few results from topics I made and one other guy on stackoverflow, nothing besides that.

I’m baffled almost noone else has this problem. I’ve rolled back to v10.1.5 and the problem is gone, aside some more super weird side effects like drop-down-menus not loading correctly.

I guess 10.2.3 is just a bad release not much people have yet.

[jangaraj]

Here is the source: SSE: Warn on dropped items in Union in Math Operation by kylebrandt · Pull Request #72682 · grafana/grafana · GitHub

Unions in SSE operations currently drop items when doing a binary operation (e.g. $A + $B) from either A or B when there isn’t a label “match” between them.

This is confusing, so to aid in this, we warn and display the count of items that where dropped, and which items they were.

IMHO you can have that math on the PromQL level, so you don’t need need to use expression.