Golang memory allocation and GC -- array + join is much better than string + string + string ...

1. alloc.go

package main

import (
	"fmt"
	"runtime"
)

func main() {
	m := 1
	s := ""
	for i := 0; i < 100001; i++ {
		s += "."
		if i%m == 0 {
			m = m * 10
			ms := runtime.MemStats{}
			runtime.ReadMemStats(&ms)
			fmt.Printf("i = %8d, TotalAlloc = %10d, HeapObjects = %8d\n",
				i, ms.TotalAlloc, ms.HeapObjects)
		}
	}
}

2. go run alloc.go

i =        0, TotalAlloc =      37816, HeapObjects =      108
i =       10, TotalAlloc =      39024, HeapObjects =      122
i =      100, TotalAlloc =      44816, HeapObjects =      214
i =     1000, TotalAlloc =     570368, HeapObjects =     1116
i =    10000, TotalAlloc =   53220720, HeapObjects =      942
i =   100000, TotalAlloc = 5309720936, HeapObjects =      146

3. GOGC=off go run alloc.go

i =        0, TotalAlloc =      37816, HeapObjects =      108
i =       10, TotalAlloc =      39024, HeapObjects =      122
i =      100, TotalAlloc =      44816, HeapObjects =      214
i =     1000, TotalAlloc =     570368, HeapObjects =     1116
i =    10000, TotalAlloc =   53213216, HeapObjects =    10118
i =   100000, TotalAlloc = 5309706304, HeapObjects =   100120

4. alloc-array.go

package main

import (
	"fmt"
	"runtime"
	"strings"
)

func main() {
	m := 1
	var s []string
	for i := 0; i < 100001; i++ {
		s = append(s, ".")
		if i%m == 0 {
			m = m * 10
			ms := runtime.MemStats{}
			runtime.ReadMemStats(&ms)
			fmt.Printf("i = %8d, TotalAlloc = %10d, HeapObjects = %8d\n",
				i, ms.TotalAlloc, ms.HeapObjects)
		}
	}
	_ = strings.Join(s, "")
}

5. go run alloc-array.go

i =        0, TotalAlloc =      49688, HeapObjects =      122
i =       10, TotalAlloc =      51344, HeapObjects =      135
i =      100, TotalAlloc =      54960, HeapObjects =      140
i =     1000, TotalAlloc =      83664, HeapObjects =      145
i =    10000, TotalAlloc =     876912, HeapObjects =      156
i =   100000, TotalAlloc =    9300256, HeapObjects =      125

6. GOGC=off go run alloc-array.go

i =        0, TotalAlloc =      49480, HeapObjects =      121
i =       10, TotalAlloc =      51072, HeapObjects =      133
i =      100, TotalAlloc =      54688, HeapObjects =      138
i =     1000, TotalAlloc =      83392, HeapObjects =      143
i =    10000, TotalAlloc =     876640, HeapObjects =      154
i =   100000, TotalAlloc =    9298048, HeapObjects =      166