1j8q.md

tags
performance memory go

lang.go.pkg.runtime

Measure memory statistics at runtime

Synopsis

import (
    "runtime"
)

func main() {
  var m runtime.MemStats

  runtime.ReadMemStats(&m)
}

Overview

You can use the runtime package to read memory statistics of your go applications

The package provides the MemStats structs that can be populated with all the memory statistics

The .Alloc attritbute represents the number of bytes currently allocated for heap objects in a go program

• This means it's the memroy currently in used by our program
• You coudl use this stats to for example:
  • Locate a memory leak
  • Find out a large allocation, in the case that there is a suddenly spike in the allocated bytes

The .TotalAlloc attribute describes the acumulate total number of bytes allocated for heap objects since the program started running

• This means this value only ever increases
• We can use this to see how memory intensive is our program throughout it's lifetime

The .Sys attribute represents the total number of bytes of memory obtained from the operating system

• This inlcudes all heap and non heap memory used
  • Like it includes memory reserved but not necessarily used
• This basically represents all the memory that the runtime has obtained from the operating system
• This can be seen as the total foot print of our program in the system's memory

The .NumGC attribute represents the number of completed garbage collection cycles since the program started

• This field is increased whenever the go runtime cleans up memory that is no longer being used
• Frecuent garbage collections might indicate high memory preasure
  • Also GC is a stop the world action that can slow down your program's operations

Cookbook

Get all the memory statistics of your program at a given point

You can use the ReadMemStats function to read all the memory statistics of your programm at a given point in time and write them to the MemStats struct for inspecting them

The attributes of the MemStats struct are all uint64 types that represent sizes in bytes if you want to get another representation like megabytes then you will need to do that conversion your self

import (
    "runtime"
)

func printMemStats() {
  var stats runtime.MemStats

  runtime.ReadMemStats(&m)

  fmt.Printf("Alloc = %v MB\n", bytesToMegabytes(stats.Alloc))
}

func bytesToMegabytes(bytes uint64) uint64 {
  kilobytes :=  bytes / 1000
  megabytes := kilobytes / 1000

  return megabytes
}

func main() {
  fmt.Println("Mem stats before:")
  printMemStats()

  mySlice := make([]int, 1_000_000)
  for index, value := range mySlice {
    mySlice[index] = value
  }

  fmt.Println("Mem stats after:")
  printMemStats()
}