How to use memory mapping to improve file reading and writing speed in Golang?

Use syscall.Mmap to implement memory mapping in Go, mapping files directly to memory to improve read and write speeds. This function returns a byte slice representing the mapped area, allowing read and write access, and sharing modifications with the file. Using syscall.Munmap to unmap can improve read and write performance. As shown in practical cases, memory mapping is much faster than traditional reading methods.

How to use memory mapping in Golang to improve file reading and writing speed

Introduction

Memory mapping is a file access technology that allows programs to map files directly to memory, thus avoiding the performance overhead caused by traditional read and write operations. In Golang, we can use the syscall.Mmap function to implement memory mapping.

Code

The following is a sample code on how to use memory mapping to read and write files in Golang:

package main

import (
    "os"
    "syscall"
    "unsafe"
)

func main() {
    // 打开文件
    f, err := os.Open("/tmp/test.txt")
    if err != nil {
        panic(err)
    }
    defer f.Close()

    // 获取文件大小
    fi, err := f.Stat()
    if err != nil {
        panic(err)
    }

    // 创建映射区域
    b, err := syscall.Mmap(int(f.Fd()), 0, int(fi.Size()), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
    if err != nil {
        panic(err)
    }

    // 数据操作
    s := []byte(string(b))
    // 您可以对 s 进行读写操作，修改将同步到文件

    // 取消映射
    err = syscall.Munmap(b)
    if err != nil {
        panic(err)
    }
}

Note:

• syscall.Mmap The function will return a byte slice representing the mapped area.
• syscall.PROT_READ and syscall.PROT_WRITE allow read and write access respectively.
• syscall.MAP_SHARED Specifies that the mapped area is shared with the file, so modifications to the mapped area will be reflected in the file.
• Be sure to use syscall.Munmap to unmap after using the mapped area.

Practical case

Let’s create a large file and use memory mapping to quickly read and write data:

package main

import (
    "fmt"
    "os"
    "syscall"
    "time"
)

func main() {
    const fileSize = 100 * 1024 * 1024 // 100MB
    const loopCount = 100

    // 创建大文件
    f, err := os.Create("/tmp/test.txt")
    if err != nil {
        panic(err)
    }
    _, err = f.Write(make([]byte, fileSize))
    if err != nil {
        panic(err)
    }
    f.Close()

    // 使用内存映射和传统方法比较读写时间
    compareTime("mmap", func() {
        for i := 0; i < loopCount; i++ {
            b := memoryMap("/tmp/test.txt")
            count := int(fileSize / 1024)
            for j := 0; j < count; j++ {
                _ = string(b[j*1024 : (j+1)*1024])
            }
            syscall.Munmap(b)
        }
    })

    compareTime("read", func() {
        for i := 0; i < loopCount; i++ {
            b, err := os.ReadFile("/tmp/test.txt")
            if err != nil {
                panic(err)
            }
            count := int(fileSize / 1024)
            for j := 0; j < count; j++ {
                _ = string(b[j*1024 : (j+1)*1024])
            }
        }
    })
}

// 使用 syscall.Mmap 获取文件映射区域
func memoryMap(file string) []byte {
    f, err := os.Open(file)
    if err != nil {
        panic(err)
    }
    defer f.Close()

    fi, err := f.Stat()
    if err != nil {
        panic(err)
    }

    b, err := syscall.Mmap(int(f.Fd()), 0, int(fi.Size()), syscall.PROT_READ, syscall.MAP_SHARED)
    if err != nil {
        panic(err)
    }
    return b
}

// 比较函数执行时间
func compareTime(name string, f func()) {
    start := time.Now()
    f()
    elapsed := time.Since(start)
    
    fmt.Printf("%s: %v\n", name, elapsed)
}

Run With the above code, you will see that the memory mapping method is significantly faster than the traditional reading method.

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