Prometheus counters: How to get current value with golang client? - go

Question

I am using counters to count the number of requests. Is there any way to get current value of a prometheus counter?
My aim is to reuse existing counter without allocating another variable.
Golang prometheus client version is 1.1.0.

Answer 1

It's easy, have a function to fetch Prometheus counter value
import (
"github.com/prometheus/client_golang/prometheus"
dto "github.com/prometheus/client_model/go"
"github.com/prometheus/common/log"
)
func GetCounterValue(metric *prometheus.CounterVec) float64 {
var m = &dto.Metric{}
if err := metric.WithLabelValues("label1", "label2").Write(m); err != nil {
log.Error(err)
return 0
}
return m.Counter.GetValue()
}

Answer 2

Currently there is no way to get the value of a counter in the official Golang implementation.
You can also avoid double counting by incrementing your own counter and use an CounterFunc to collect it.
Note: use integral type and atomic to avoid concurrent access issues
// declare the counter as unsigned int
var requestsCounter uint64 = 0
// register counter in Prometheus collector
prometheus.MustRegister(prometheus.NewCounterFunc(
prometheus.CounterOpts{
Name: "requests_total",
Help: "Counts number of requests",
},
func() float64 {
return float64(atomic.LoadUint64(&requestsCounter))
}))
// somewhere in your code
atomic.AddUint64(&requestsCounter, 1)

Answer 3

It is possible to read the value of a counter (or any metric) in the official Golang implementation. I'm not sure when it was added.
This works for me for a simple metric with no vector:
func getMetricValue(col prometheus.Collector) float64 {
c := make(chan prometheus.Metric, 1) // 1 for metric with no vector
col.Collect(c) // collect current metric value into the channel
m := dto.Metric{}
_ = (<-c).Write(&m) // read metric value from the channel
return *m.Counter.Value
}
Update: here's a more general version that works with vectors and on histograms...
// GetMetricValue returns the sum of the Counter metrics associated with the Collector
// e.g. the metric for a non-vector, or the sum of the metrics for vector labels.
// If the metric is a Histogram then number of samples is used.
func GetMetricValue(col prometheus.Collector) float64 {
var total float64
collect(col, func(m dto.Metric) {
if h := m.GetHistogram(); h != nil {
total += float64(h.GetSampleCount())
} else {
total += m.GetCounter().GetValue()
}
})
return total
}
// collect calls the function for each metric associated with the Collector
func collect(col prometheus.Collector, do func(dto.Metric)) {
c := make(chan prometheus.Metric)
go func(c chan prometheus.Metric) {
col.Collect(c)
close(c)
}(c)
for x := range c { // eg range across distinct label vector values
m := dto.Metric{}
_ = x.Write(&m)
do(m)
}
}

Answer 4

While it is possible to obtain counter values in github.com/prometheus/client_golang as pointed at this answer, this looks too complicated. This can be greatly simplified by using an alternative library for exporing Prometheus metrics - github.com/VictoriaMetrics/metrics:
import (
"github.com/VictoriaMetrics/metrics"
)
var requestsTotal = metrics.NewCounter(`http_requests_total`)
//...
func getRequestsTotal() uint64 {
return requestsTotal.Get()
}
E.g. just call Get() function on the needed counter.