Example usage of runtime.ReadMemStats function

readMemStatsExample.go

package main

import (
	"fmt"
	"runtime"
	"strconv"
	"time"
)

func printMemStats(message string, rtm runtime.MemStats){
	fmt.Println("\n===", message, "===")
	fmt.Println("Mallocs: ", rtm.Mallocs)
	fmt.Println("Frees: ", rtm.Frees)
	fmt.Println("LiveObjects: ", rtm.Mallocs - rtm.Frees)
	fmt.Println("PauseTotalNs: ", rtm.PauseTotalNs)
	fmt.Println("NumGC: ", rtm.NumGC)
	fmt.Println("LastGC: ", time.UnixMilli(int64(rtm.LastGC/1_000_000)))
	fmt.Println("HeapObjects: ", rtm.HeapObjects)
	fmt.Println("HeapAlloc: ", rtm.HeapAlloc)
}

func main() {
	var rtm runtime.MemStats
	runtime.ReadMemStats(&rtm)
	printMemStats("Start", rtm)

	a := make([]int64, 0)
	var i int64
	for i = 0 ; i < 10_000_000; i++ {
		a = append(a, i)
	}

	runtime.ReadMemStats(&rtm)
	printMemStats("After 10 million int64 appends", rtm)

	var b []string
	var j int
	for j = 0 ; j < 10_000_000; j++ {
		b = append(b, "hello"+strconv.Itoa(j))
	}

	runtime.ReadMemStats(&rtm)
	printMemStats("After 10 million string appends", rtm)

	runtime.GC()

	runtime.ReadMemStats(&rtm)
	printMemStats("After forced GC", rtm)
}

Output

=== Start ===
Mallocs:  228
Frees:  3
LiveObjects:  225
PauseTotalNs:  0
NumGC:  0
LastGC:  1970-01-01 05:30:00 +0530 IST
HeapObjects:  225
HeapAlloc:  137320

=== After 10 million int64 appends ===
Mallocs:  341
Frees:  104
LiveObjects:  237
PauseTotalNs:  557209
NumGC:  17
LastGC:  2021-11-29 09:36:08.33 +0530 IST
HeapObjects:  237
HeapAlloc:  152735680

=== After 10 million string appends ===
Mallocs:  20000307
Frees:  8709822
LiveObjects:  11290485
PauseTotalNs:  933867
NumGC:  23
LastGC:  2021-11-29 09:36:09.316 +0530 IST
HeapObjects:  11290485
HeapAlloc:  478861336

=== After forced GC ===
Mallocs:  20000321
Frees:  20000076
LiveObjects:  245
PauseTotalNs:  1018576
NumGC:  24
LastGC:  2021-11-29 09:36:09.532 +0530 IST
HeapObjects:  245
HeapAlloc:  136448

thanks