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file_manager.go
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package mydb
import (
"encoding/binary"
"fmt"
"log"
"os"
"syscall"
)
type fileManager struct {
pageSize uint64
pageSizeInt int
pageSizeInt64 int64
file *os.File
fd int
}
const (
rootBegin = 0
frontBegin = 8
recycleBegin = 16
)
func newFileManager(name string, pageSize uint64) (*fileManager, error) {
file, err := os.OpenFile(name, syscall.O_RDWR|os.O_CREATE, 0666)
if err != nil {
return nil, err
}
fm := &fileManager{
pageSize: pageSize,
pageSizeInt: int(pageSize),
pageSizeInt64: int64(pageSize),
file: file,
fd: int(file.Fd()),
}
if fm.fileSize() == 0 {
err = syscall.Ftruncate(fm.fd, fm.pageSizeInt64)
if err != nil {
return nil, err
}
page := fm.allocatePage(pageTypeLeaf)
fm.setRoot(page.offset)
fm.setFront(page.offset)
}
return fm, nil
}
func (f *fileManager) fileSize() int64 {
info, err := f.file.Stat()
if err != nil {
panic(err)
}
return info.Size()
}
func (f *fileManager) rootPage() *page {
buf, err := syscall.Mmap(f.fd, 0, f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
index := binary.BigEndian.Uint64(buf[rootBegin:])
return f.page(index)
}
func (f *fileManager) frontPage() *page {
buf, err := syscall.Mmap(f.fd, 0, f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
return f.page(binary.BigEndian.Uint64(buf[frontBegin:]))
}
func (f *fileManager) setRoot(root uint64) {
buf, err := syscall.Mmap(f.fd, 0, f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
binary.BigEndian.PutUint64(buf[rootBegin:], root)
}
func (f *fileManager) setFront(front uint64) {
buf, err := syscall.Mmap(f.fd, 0, f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
binary.BigEndian.PutUint64(buf[frontBegin:], front)
}
// page 获取page
func (f *fileManager) page(offset uint64) *page {
buf, err := syscall.Mmap(f.fd, int64(offset), f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
log.Println(err, offset)
panic(err)
}
return &page{offset: offset, buf: buf, size: uint16(len(buf))}
}
// allocatePage 分配页空间，首先会尝试从回收空间分配，再申请新的磁盘空间
func (f *fileManager) allocatePage(pageType uint16) *page {
// 从回收空间获取
buf, err := syscall.Mmap(f.fd, 0, f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
recycleOffset := binary.BigEndian.Uint64(buf[recycleBegin:])
if recycleOffset != 0 {
buf, err := syscall.Mmap(f.fd, int64(recycleOffset), f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
page := newPage(buf, recycleOffset, pageType)
binary.BigEndian.PutUint64(buf[recycleBegin:], page.next())
return page
}
// 申请磁盘空间
fileSize := f.fileSize()
err = syscall.Ftruncate(f.fd, fileSize+f.pageSizeInt64)
if err != nil {
panic(err)
}
buf, err = syscall.Mmap(f.fd, fileSize, f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
return newPage(buf, uint64(fileSize), pageType)
}
// recycle 回收空间
func (f *fileManager) recycle(page *page) {
page._reset()
page.setPageType(pageTypeRecycle)
buf, err := syscall.Mmap(f.fd, 0, f.pageSizeInt, syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
panic(err)
}
page.setNext(binary.BigEndian.Uint64(buf[recycleBegin:]))
binary.BigEndian.PutUint64(buf[recycleBegin:], page.offset)
}
type statisticsResult struct {
fileSize uint64
pageSize uint64
totalPageNum uint64
branchPageNum int
leafPageNum int
recyclePageNum int
depth int
recordNum int
}
func (s *statisticsResult) String() string {
return fmt.Sprintf("fileSize:%dB, totalPageNum:%d, branchPageNum:%d, leafPageNum:%d, recyclePageNum:%d, depth:%d, recordNum:%d",
s.fileSize, s.fileSize/s.pageSize, s.branchPageNum, s.leafPageNum, s.recyclePageNum, s.depth, s.recordNum)
}
// statistics page统计
func (f *fileManager) statisticsPage() *statisticsResult {
var result statisticsResult
result.pageSize = f.pageSize
info, err := f.file.Stat()
if err != nil {
panic(err)
}
result.fileSize = uint64(info.Size())
result.totalPageNum = result.fileSize / f.pageSize
// 统计枝干页和叶子页数量
offset := f.pageSize
for offset < result.fileSize {
page := f.page(offset)
switch page.pageType() {
case pageTypeBranch:
result.branchPageNum++
case pageTypeLeaf:
result.leafPageNum++
result.recordNum += page.count()
case pageTypeRecycle:
result.recyclePageNum++
}
offset += f.pageSize
}
// 统计b+树的深度
result.depth = 1
page := f.frontPage()
for {
parent := page.parent()
if parent == 0 {
break
}
result.depth++
page = f.page(parent)
}
return &result
}