How to create and use histograms and percentiles with expvar in Go?

To create and use histograms and percentiles with expvar in Go, follow these steps:

Import the necessary packages:
import ( "expvar" "math/rand" "time" "github.com/codahale/hdrhistogram" )
Initialize and register a histogram variable:
// Create a histogram with predefined values histogram := hdrhistogram.New(1, 1e9, 3) expvar.Publish("my_histogram", histogram)
Measure and record values in the histogram:
// Record a random value in the histogram value := rand.Intn(100) histogram.RecordValue(int64(value))
Calculate and display percentiles:
// Calculate and display percentiles count := float64(histogram.TotalCount()) perc90 := histogram.ValueAtQuantile(90.0) perc99 := histogram.ValueAtQuantile(99.0) println("Total Count: ", count) println("90th Percentile: ", perc90) println("99th Percentile: ", perc99)
Note: The hdrhistogram library provides methods like ValueAtQuantile() to calculate percentiles.

Now you can run your Go program and observe the recorded histogram and percentiles in your expvar metrics.

Remember to import the net/http package and use http.Handle to serve the expvar metrics over HTTP so you can view them. For example:

import (
    "net/http"
    _ "net/http/pprof"
)

func main() {
    // ...your code...

    // Serve expvar metrics over HTTP
    http.Handle("/debug/vars", expvar.Handler())
    go http.ListenAndServe(":8080", nil)

    // ...your code...
}

You can then access the expvar metrics by visiting http://localhost:8080/debug/vars in your web browser or making a GET request programmatically.