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db.go
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db.go
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package bitcask_go
import (
"errors"
"io"
"os"
"sync"
)
/**
*@Author icepan
*@Date 11/17/21 19:00
*@Describe
**/
const LogFileName = "bitcask.db"
var (
KeyIsNotExist = errors.New("key is not exist")
)
type DB struct {
cache sync.Map
dbFile *DBFile
dirPath string
}
func Open(dirPath string) (*DB, error) {
dbFile, err := newDBFile(dirPath + "/" + LogFileName)
if err != nil {
return nil, err
}
db := &DB{
cache: sync.Map{},
dbFile: dbFile,
dirPath: dirPath,
}
if err = db.load(); err != nil {
return nil, err
}
return db, nil
}
func (db *DB) load() error {
var offset int64
for {
e, err := db.dbFile.Read(offset)
if err != nil {
if err != io.EOF {
return err
}
return nil
}
db.cache.Store(string(e.Key), offset)
offset += e.Size()
}
}
func (db *DB) Get(key string) (val string, err error) {
mapData, ok := db.cache.Load(key)
if !ok {
return "", KeyIsNotExist
}
offset := mapData.(int64)
e, err := db.dbFile.Read(offset)
if err != nil {
return "", err
}
return string(e.Val), nil
}
func (db *DB) Del(key string) error {
if _, ok := db.cache.Load(key); !ok {
return KeyIsNotExist
}
e := NewEntry([]byte(key), nil, DEL)
if err := db.dbFile.Write(e); err != nil {
return err
}
db.cache.Delete(key)
return nil
}
func (db *DB) Add(key string, val string) error {
offset := db.dbFile.Offset
e := NewEntry([]byte(key), []byte(val), ADD)
if err := db.dbFile.Write(e); err != nil {
return err
}
db.cache.Store(key, offset)
return nil
}
func (db *DB) Merge() error {
var offset int64
var newEntries []*Entry
for {
e, err := db.dbFile.Read(offset)
if err != nil {
if err != io.EOF {
return err
}
break
}
dataMap, ok := db.cache.Load(string(e.Key))
if !ok {
offset += e.Size()
continue
}
//内存中索引和文件里一样则表示数据是可以持久化的
newOffset := dataMap.(int64)
if newOffset == offset {
newEntries = append(newEntries, e)
}
offset += e.Size()
}
if err := os.Truncate(db.dirPath+"/"+LogFileName, 0); err != nil {
return err
}
db.dbFile.Offset = 0
offset = 0
for _, entry := range newEntries {
if err := db.dbFile.Write(entry); err != nil {
return err
}
db.cache.Store(string(entry.Key), offset)
offset += entry.Size()
}
return nil
}