opentelemetry-go
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open-telemetry
How to implement Prometheus Gauge Set method in open-telemetry？
Problem Statement
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I'm trying to migrate an project's metric implement from Prometheus to open-telemetry，it heavily use gauge.Set to measure values with different labels group. For example:
It have an gauge metric for conn pool stats, defined as:
conn_pool_stat{type=?}
and type's value could be one of: free、running as so on.
On other hand, another library we used only expose an Store method to the user, which is been called when the library want to set a metric to an concrete value (with different labels group), we implement Store use gauge.Set method. but when we migrate to open-telemetry，we only have two choice:
- Float64UpDownCounter，but it only have an Add method
- Float64ObservableGauge，but it only record value when callback is perform, and the library will call
Storeat any time.
base on this discription，how should implement gauge.Set method in open-telemetry with different label groups？
I have search for previous issue，and found https://github.com/open-telemetry/opentelemetry-go/issues/708#issuecomment-820646727 is and similar requests.
Proposed Solution
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Related to https://github.com/open-telemetry/opentelemetry-specification/issues/2318
The specification have add an sync gauge at https://github.com/open-telemetry/opentelemetry-specification/pull/3540，is there any plan to implement it in go？
The specification have add an sync gauge at https://github.com/open-telemetry/opentelemetry-specification/pull/3540，is there any plan to implement it in go？
When it becomes stable in the specification, yes.
You can (relatively easily) work around this using asynchronous gauges:
func ExampleSynchronousGauge() {
myGauge := NewFloat64Gauge()
_, err := meter.Float64ObservableGauge(
"my.metric.name",
metric.WithUnit("s"),
metric.WithInt64Callback(myGauge.Callback),
)
if err != nil {
panic(err)
}
// use your synchronous gauge!
myGauge.Set(3.14, attribute.NewSet(attribute.String("one", "1")))
myGauge.Set(3.14159, attribute.NewSet(attribute.String("one", "bar")))
// Later, if I want to stop exporting that attribute set:
myGauge.Delete(attribute.NewSet(attribute.String("one", "1")))
}
func NewFloat64Gauge() *Float64Gauge {
return &Float64Gauge{observations: make(map[attribute.Set]float64)}
}
type Float64Gauge struct {
observations map[attribute.Set]float64
}
// Callback implements the callback function for the underlying asynchronous gauge
// it observes the current state of all previous Set() calls.
func (f *Float64Gauge) Callback(ctx context.Context, o metric.Float64Observer) error {
for attrs, val := range f.observations {
o.Observe(val, metric.WithAttributeSet(attrs))
}
return nil
}
func (f *Float64Gauge) Set(val float64, attrs attribute.Set) {
f.observations[attrs] = val
}
func (f *Float64Gauge) Delete(attrs attribute.Set) {
delete(f.observations, attrs)
}
Seems sync gauge already released in specs (https://github.com/open-telemetry/opentelemetry-specification/releases/tag/v1.25.0)
Are there any support plans for golang?
I've worked it around by implementing gauge using the example of OpenTelemetry telemetrygen tool, which submits the Gauge metrics by default: https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/cmd/telemetrygen/internal/metrics/worker.go#L52-L64
Will replace my workaround with the original synchronous Gauge once it's implemented.
