Having metrics with different label compositions seems *fine to me*. In the 
end a metric is nothing more than a set of time series with the same value 
for the label `__name__`. So there is no difference for the storage engine. 

I would just ensure that your data stays aggregatable. What do I mean by 
this? Let's take the following example:

```
 subsystem_message_total{name="foo", direction="in"}=100
 subsystem_message_total{name="foo", direction="out"}=100
 subsystem_message_total{name="bar"}=100
```

The query `sum(subsystem_message_total)` returns `300` which is correct. 
But if it looks like this:

```
 subsystem_message_total{name="foo", direction="in"}=100
 subsystem_message_total{name="foo", direction="out"}=100
 subsystem_message_total{name="foo"}=200  
 subsystem_message_total{name="bar"}=100
```

The query  `sum(subsystem_message_total)` will return `500`. So to work 
around this you would have to always remember to only include series with 
xor without a `direction` label.
John Dexter schrieb am Montag, 26. Oktober 2020 um 15:36:55 UTC+1:

> I have a use-case where we monitor multiple, very different systems 
> through a variety of protocols but one common thing is each sends updates 
> to our server and most allow us to send messages to them too.
>
> This seems a perfect example of labels... 
> subsystem_message_total[subsystem-name,direction] for instance.
>
> But one of our systems has 2 components, the others don't. I'm unsure what 
> happens if this subsystem uses a 3rd label [component] and the others do 
> not. Is this bad practice? Will it cause problems in storing/querying data?
> Subsystems could each have their own metric name instead of using labels, 
> but that sounds pretty ugly too.
>
> What is the best approach here?
>
> Thanks. 
>

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