Go map memory

main.go

package main

import (
	"fmt"
	"runtime"

	"golang.org/x/text/language"
	"golang.org/x/text/message"
)

var p = message.NewPrinter(language.English)

func profile(f func() string) {
	var mem runtime.MemStats
	runtime.GC()
	runtime.ReadMemStats(&mem)
	before := mem.Alloc
	title := f()
	runtime.ReadMemStats(&mem)
	after := mem.Alloc
	p.Printf("%s:%d bytes\n", title, after-before)
}

func main() {
	var i, j int32

	numUsers := int32(100000)

	profile(func() string {
		v := map[int32]int32{}
		for i = 0; i < numUsers; i++ {
			v[i] = i
		}
		return fmt.Sprintf("%T", v)
	})

	profile(func() string {
		v := map[uint16]uint16{}
		for i = 0; i < numUsers; i++ {
			v[uint16(i)] = uint16(i)
		}
		return fmt.Sprintf("%T", v)
	})

	numUsers = int32(10000)
	max := int32(5000)

	profile(func() string {
		v := map[int32]map[int32]float32{}

		for i = 0; i < numUsers; i++ {
			v[i] = map[int32]float32{}
			for j = 0; j < max; j++ {
				v[i][j] = 0.0
			}
		}

		return fmt.Sprintf("%T", v)
	})

	profile(func() string {
		v := map[uint16]map[uint16]uint8{}

		for i = 0; i < numUsers; i++ {
			v[uint16(i)] = map[uint16]uint8{}
			for j = 0; j < max; j++ {
				// Quantization
				v[uint16(i)][uint16(j)] = uint8(0.0 * 255)
			}
		}

		return fmt.Sprintf("%T", v)
	})
}

map[int32]int32:3,269,192 bytes
map[uint16]uint16:1,867,928 bytes
map[int32]map[int32]float32:1,125,422,336 bytes
map[uint16]map[uint16]uint8:664,942,024 bytes