example/prometheus: histogram has only +Inf buckets

[jpkrohling]

Description

The Prometheus example is a bit confusing, with three histogram measurements resulting in only two buckets (2x +Inf), each with a value of 1:

# HELP ex_com_two 
# TYPE ex_com_two histogram
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="+Inf"} 1
ex_com_two_sum{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 2
ex_com_two_count{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="+Inf"} 1
ex_com_two_sum{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 2
ex_com_two_count{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 1

Reading the code, I would expect multiple buckets, some of them perhaps empty. Turns out, config.DefaultHistogramBoundaries is an empty list of values:

opentelemetry-go/example/prometheus/main.go

Lines 41 to 50 in f1971b3

	config := prometheus.Config{}
	c := controller.New(
	processor.NewFactory(
	selector.NewWithHistogramDistribution(
	histogram.WithExplicitBoundaries(config.DefaultHistogramBoundaries),
	),
	aggregation.CumulativeTemporalitySelector(),
	processor.WithMemory(true),
	),
	)

Changing the example so that the first param to the factory is selector.NewWithHistogramDistribution() results in the following, which is already closer to my expectation:

# HELP ex_com_two 
# TYPE ex_com_two histogram
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.005"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.01"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.025"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.05"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.1"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.25"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.5"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="1"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="2.5"} 1
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="5"} 1
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="10"} 1
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="+Inf"} 1
ex_com_two_sum{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 2
ex_com_two_count{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.005"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.01"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.025"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.05"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.1"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.25"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="0.5"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="1"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="2.5"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="5"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="10"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="+Inf"} 2
ex_com_two_sum{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 14
ex_com_two_count{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 2

Perhaps the example could show how to specify explicit buckets. For instance, by changing the original example to have the following config:

	config := prometheus.Config{
		DefaultHistogramBoundaries: []float64{1, 2, 5, 10, 20, 50},
	}

This would result in the following buckets:

# HELP ex_com_two 
# TYPE ex_com_two histogram
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="1"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="2"} 0
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="5"} 1
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="10"} 1
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="20"} 1
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="50"} 1
ex_com_two_bucket{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="+Inf"} 1
ex_com_two_sum{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 2
ex_com_two_count{ex_com_lemons="13",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="1"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="2"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="5"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="10"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="20"} 2
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="50"} 2
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0",le="+Inf"} 2
ex_com_two_sum{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 14
ex_com_two_count{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:prometheus",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.2.0"} 2

Environment

• OS: Fedora 35
• Architecture: amd64
• Go Version: 1.17
• opentelemetry-go version: 1ea6ee3 (main as of this writing)

Steps To Reproduce

1. cd example/prometheus
2. go run .
3. open localhost:2222

[NeesonD]

@MrAlias

1. Hi, bro. why func NewWithHistogramDistribution() can set multi histogram.Option params ? I found just the last one set in config.explicitBoundaries.
2. How do I set up a separate bucket for each Histogram.

like this:

metricServerReqDur = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Namespace:   serverNamespace,
		Subsystem:   "requests",
		Name:        "duration_ms",
		Help:        "http server requests duration(ms).",
		ConstLabels: nil,
		Buckets:     []float64{5, 10, 25, 50, 100, 250, 500, 1000},
	}, []string{"path"})