It's about aggregation and doing math on the data.
sum(node_cpu_seconds_total) makes sense, because all of the various modes
can be added together.
Say you had labels for memory:
node_memory_bytes{mem_type="MemAvailable"} 1.00470784e+08
node_memory_bytes{mem_type="MemFree"} 5.3211136e+07
node_memory_bytes{mem_type="MemTotal"} 2.68435456e+08
sum(node_memory_bytes) is nonsensical because "MemTotal" + "MemFree" +
"MemAvailable" doesn't add up to anything useful.
But, having them as separate metrics makes queries like
"node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes" work out
Think of metric names and labels as column vs rows in a spreadsheet.
Aggregation operators like sum() avg() min() max() work vertically.
Mathematical operators like + - / * work horizontally.
On Sun, May 17, 2020 at 4:08 AM Daniel Lo Nigro <[email protected]> wrote:
> I've noticed that for some metrics, Prometheus node_exporter will use one
> metric name and separate labels. For example, CPU usage has a "mode" label:
>
> node_cpu_seconds_total{cpu="0",mode="idle"} 320045.23
> node_cpu_seconds_total{cpu="0",mode="steal"} 0
> node_cpu_seconds_total{cpu="0",mode="system"} 3703.1
> node_cpu_seconds_total{cpu="0",mode="user"} 4713.87
>
> Whereas for other metrics, it uses separate metric names. For example,
> memory usage:
>
> node_memory_MemAvailable_bytes 1.00470784e+08
> node_memory_MemFree_bytes 5.3211136e+07
> node_memory_MemTotal_bytes 2.68435456e+08
>
> Both are bounded (there's a fixed number of CPU modes, and a fixed number
> of memory fields) so I'm not sure why the implementation differs between
> the two.
>
> Is this intentional? If so, is there a guideline or best practice as to
> when to do the former vs when to do the latter?
>
> Thanks!
>
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