Comparison of memory footprint of map[int]bool vs. map[int]struct{}

set_implementations.go

package main

import (
	"fmt"
	"math/rand"
	"runtime"
)

func main() {
	BoolImplMemoryFootprint()
	EmptyStructImplMemoryFootprint()
}

type setbool map[int]bool

func BoolImplMemoryFootprint() {
	fmt.Println()
	fmt.Println("set as map[int]bool")

	M := 20_000
	K := 300

	Sink = nil
	showMem()
	rng := rand.New(rand.NewSource(42))
	a := make([]setbool, K)

	for i := range a {
		m := make(setbool, M)
		for k := 0; k <= M; k++ {
			if rng.Intn(2) == 1 {
				m[k] = true
			}
		}
		a[i] = m
	}
	showMem()
	Sink = a
}

type setstruct map[int]struct{}

func EmptyStructImplMemoryFootprint() {
	fmt.Println()
	fmt.Println("set as map[int]struct{}")

	M := 20_000
	K := 300

	Sink = nil
	showMem()
	rng := rand.New(rand.NewSource(42))
	a := make([]setstruct, K)

	for i := range a {
		m := make(setstruct, M)
		for k := 0; k <= M; k++ {
			if rng.Intn(2) == 1 {
				m[k] = struct{}{}
			}
		}
		a[i] = m
	}
	showMem()
	Sink = a
}

func showMem() {
	runtime.GC()
	var memstat runtime.MemStats
	runtime.ReadMemStats(&memstat)
	fmt.Println("HeapAlloc is", memstat.HeapAlloc, "bytes")
}

var Sink any

Output on my workstation ():

% go run ./set_implementations.go

set as map[int]bool
HeapAlloc is 141792 bytes
HeapAlloc is 115691680 bytes

set as map[int]struct{}
HeapAlloc is 142184 bytes
HeapAlloc is 105865088 bytes

In this examples, bool values use 9% more memory.