measure GC for different maps

gctest.go

package main
import (
	"strconv"
	"fmt"
	"os"
	"runtime"
	"time"
)
// run this program as:
/*
#!/bin/bash
for t in 1 2; do go run gctest.go $t; done
*/
func timeGC() time.Duration {
	start := time.Now()
	runtime.GC()
	return time.Since(start)
}

func main() {
	const N = 30e6
	if len(os.Args) != 2 {
		fmt.Printf("usage: %s [1 2]\n(number selects the test)\n", os.Args[0])
		return
	}
	switch os.Args[1] {
	case "1":
		// create a big map of strings. since strings contain pointers, we expect this to have more pressure on GC.
		m := make(map[string]string)
		for i := 0; i < N; i++ {
			n := strconv.Itoa(i)
			m[n] = n
		}
		runtime.GC()
		fmt.Printf("With a map of strings, GC took: %s\n", timeGC())
		_ = m["0"]
	case "2":
		// create a map of ints. We want to store strings in the map but unlike in case 1, we will hash the strings to ints (which have no pointer)
		// so we expect less pressure on GC. We are using  strconv.Atoi(str) as a stand-in for a proper hash function
		m := make(map[int]int)
		for i := 0; i < N; i++ {
			str := strconv.Itoa(i)
			// hash string to int
			n,_ := strconv.Atoi(str)
			m[n] = n
		}
		runtime.GC()
		fmt.Printf("With map of strings(that are hashed to ints), GC took:: %s\n", timeGC())
		_ = m[0]
	}
}