# Metrics类型

Prometheus定义了4中不同的指标类型(metric type)：Counter（计数器）、Gauge（仪表盘）、Histogram（直方图）、Summary（摘要）。

在NodeExporter返回的样本数据中，其注释中也包含了该样本的类型。例如：

```
# HELP node_cpu_seconds_total Seconds the cpus spent in each mode.
# TYPE node_cpu_seconds_total counter
node_cpu_seconds_total{cpu="0",mode="idle"} 927490.95
node_cpu_seconds_total{cpu="0",mode="iowait"} 27.74
...
```

上面的就是counter类型的指标。

## Counter：只增不减的计数器

Counter类型的指标数据，只增不减（除非系统发生重置）。常见的有`node_cpu_seconds_total{cpu="x",mode="idle"}`，它表示的意思是序号为`x`的cpu从开机到当前的这段时间内，cpu处于空闲（`idle`）状态的时间总和。

## Gauge：可增可减的仪表盘

Gauge类型的指标数据，可增可减，比如内存剩余量`node_memory_MemAvailable`

## to be continued


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