Experiments with pagecache-centric logging and recovery in Go.

crash_recover.go

package main

// crash_recover.go experiments with recovering from a file that suddenly
// crashed (files are written without sync or close.)

import (
	"encoding/binary"
	"fmt"
	"math/rand"
	"os"
	"runtime"
	"time"
)

// Goal: append `recovery.log` with consecutive integers.
func main() {

	runtime.GOMAXPROCS(4)
	rand.Seed(time.Now().UnixNano())

	file, err := os.OpenFile("recovery.log", os.O_RDWR|os.O_CREATE, 0666)
	if nil != err {
		panic(err)
	}

	n := read(file) // last number in file was n
	write(file, n)  // continue writing from n

}

// read reads from the given file and reports the last entry in the file.
func read(file *os.File) uint32 {

	if _, err := file.Seek(-4, os.SEEK_END); nil != err {
		fmt.Println("File was empty.")
		return 0
	}

	var n uint32
	if err := binary.Read(file, binary.LittleEndian, &n); nil != err {
		panic(err)
	}

	fmt.Println("Last entry was \t\t\t\t", n)
	return n

}

// write appends to the given file and exits with probability 0.0001.
func write(file *os.File, n uint32) {

	file.Seek(0, os.SEEK_END)
	for {

		err := binary.Write(file, binary.LittleEndian, n)
		if nil != err {
			panic(err)
		}

		if rand.Float32() < 0.0001 {
			fmt.Println("Last number written was \t\t", n)
			os.Exit(0)
		}

		n++

	}

}