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page.go
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page.go
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package mydb
import (
"bytes"
"encoding/binary"
"fmt"
)
const recordsDefaultBegin = 64
const (
pageTypeBranch = 0 // 枝干
pageTypeLeaf = 1 // 叶子
pageTypeRecycle = 2 // 被回收
)
const (
byte2 = 2
byte8 = 8
)
const (
flag8Parent = 0 // 页父节点位置
flag8Pre = 8 // 页前置节点位置
flag8Next = 16 // 页后置节点位置
flag2Type = 32 // 页类型
flag2RecordBegin = 34 // 记录空间开始位置
flag2RecycleBegin = 36 // 回收空间开始位置
flag2FreeBegin = 38 // 空闲空间开始位置
flag2DirBegin = 40 // 目录空间开始位置
)
type page struct {
offset uint64
buf []byte
size uint16
minDirBegin uint16
}
func newPage(buf []byte, offset uint64, pageType uint16) *page {
p := &page{
offset: offset,
buf: buf,
size: uint16(len(buf)),
}
p.minDirBegin = (p.size - recordsDefaultBegin) / 2 / 8
p._setIndexByFlag2(flag2Type, pageType)
if p.size == 0 {
panic("size == 0")
}
return p
}
func (p *page) display() {
all := p.all()
for i := range all {
all[i].display()
fmt.Println()
}
}
func (p *page) pageType() uint16 {
return p._indexByFlag2(flag2Type)
}
func (p *page) setPageType(pageType uint16) {
p._setIndexByFlag2(flag2Type, pageType)
}
func (p *page) offsetBuf() []byte {
buf := make([]byte, byte8)
binary.BigEndian.PutUint64(buf, p.offset)
return buf
}
func (p *page) parent() uint64 {
return p._indexByFlag8(flag8Parent)
}
func (p *page) setParent(index uint64) {
p._setIndexByFlag8(flag8Parent, index)
}
func (p *page) pre() uint64 {
return p._indexByFlag8(flag8Pre)
}
func (p *page) setPre(index uint64) {
p._setIndexByFlag8(flag8Pre, index)
}
func (p *page) next() uint64 {
return p._indexByFlag8(flag8Next)
}
func (p *page) setNext(index uint64) {
p._setIndexByFlag8(flag8Next, index)
}
func (p *page) get(key []byte) ([]byte, bool) {
_, r := p.find(key)
if r == nil || !bytes.Equal(r.Key, key) {
return nil, false
}
return r.Value, true
}
// set 设置
// isNew 是否是新纪录
// isEnoughSpace 是否空间足够
func (p *page) set(key, value []byte) (isNew bool, isEnoughSpace bool) {
isEnoughSpace = true
dir, current := p.find(key)
// record存在且原地址空间符合，直接更新
isNew = current == nil || !bytes.Equal(current.Key, key)
if !isNew {
new := *current
new.Value = value
if new.needSpaceLen() <= current.spaceLen {
p._setRecord(&new)
isEnoughSpace = true
return
}
p._deleteRecord(*current)
p._dirDelete(*dir, *current)
// 这里可能删除目录，或者目录产生移位，还可能目录合并，需要重新获取
dir = p._dirFind(key)
}
// 原地址空间不符合或者记录不存在，需要添加
// 找到添加pre位置
preOffset := uint16(0)
if current != nil {
if isNew {
preOffset = current.offset
} else {
preOffset = current.pre
}
}
new := &record{Key: key, Value: value}
offset, spaceLen, ok := p._getSpace(new.needSpaceLen())
if !ok {
// 这里存在更新的时候，空间不足的情况
isEnoughSpace = false
return
}
new.offset = offset
new.spaceLen = spaceLen
if preOffset == 0 {
recordBegin := p._indexByFlag2(flag2RecordBegin)
p._setIndexByFlag2(flag2RecordBegin, new.offset)
new.pre = 0
new.next = recordBegin
p._setRecord(new)
if recordBegin != 0 {
next := p._record(recordBegin)
next.pre = new.offset
p._setRecord(next)
}
} else {
pre := p._record(preOffset)
preNext := pre.next
pre.next = new.offset
p._setRecord(pre)
new.pre = pre.offset
new.next = preNext
p._setRecord(new)
if preNext != 0 {
next := p._record(preNext)
next.pre = new.offset
p._setRecord(next)
}
}
p._dirAdd(dir, new)
return
}
func (p *page) delete(key []byte) bool {
d, r := p.find(key)
if r == nil || !bytes.Equal(r.Key, key) {
return false
}
p._deleteRecord(*r)
p._dirDelete(*d, *r)
return true
}
func (p *page) min() []byte {
beginIndex := p._indexByFlag2(flag2RecordBegin)
if beginIndex == 0 {
return []byte("")
}
record := p._record(beginIndex)
return record.Key
}
func (p *page) updateMinKey(key []byte) bool {
min := p.min()
value, _ := p.get(min)
p.delete(min)
_, isEnoughSpace := p.set(key, value)
return isEnoughSpace
}
func (p *page) isNil() bool {
return p._indexByFlag2(flag2RecordBegin) == 0
}
// splitFront 溢出前面record
func (p *page) splitFront(key, value []byte) []*record {
all := p.all()
all, _ = appendToSortedRecords(all, &record{Key: key, Value: value})
p._reset()
var useSpace uint16 = 0
overflow := make([]*record, 0, 10)
recordMaxSize := p._recordMaxSize()
for i := range all {
// i != len(all) 这里要保证，p不是一个空页
if useSpace < recordMaxSize && i != len(all)-1 {
overflow = append(overflow, all[i])
useSpace += all[i].needSpaceLen()
} else {
p.set(all[i].Key, all[i].Value)
}
}
return overflow
}
// splitBehind 分裂节点，溢出后面record
// first return 溢出的记录
// second return 新插入的记录位置是否在前置节点
func (p *page) splitBehind(key, value []byte) ([]*record, bool) {
all := p.all()
all, _ = appendToSortedRecords(all, &record{Key: key, Value: value})
p._reset()
var useSpace uint16 = 0
overflow := make([]*record, 0, 10)
recordMaxSize := p._recordMaxSize()
for i := range all {
if useSpace < recordMaxSize {
p.set(all[i].Key, all[i].Value)
useSpace += all[i].needSpaceLen()
} else {
overflow = append(overflow, all[i])
}
}
isFront := true
if len(overflow) > 0 && bytes.Compare(key, overflow[0].Key) >= 0 {
isFront = false
}
return overflow, isFront
}
func (p *page) query(min, max []byte) []*record {
records := make([]*record, 0, 10)
_, r := p.find(min)
if r == nil {
recordBegin := p._indexByFlag2(flag2RecordBegin)
if recordBegin == 0 {
return nil
}
r = p._record(recordBegin)
}
for {
if r.match(min, max) {
records = append(records, r)
}
if r.next == 0 {
break
}
r = p._record(r.next)
}
return records
}
// find 查找key所在的directory以及record，record.key =< key
// 页为空或或者key小于所有元素 dir == nil record == nil
// 中间 dir != nil record != nil
// 大于所有元素 dir == last_dir record == last record
func (p *page) find(key []byte) (*dir, *record) {
dir := p._dirFind(key)
if dir == nil {
return nil, nil
}
offset := dir.recordOffset
r := p._record(offset)
for {
if r.next == 0 {
return dir, r
}
next := p._record(r.next)
if bytes.Compare(next.Key, key) > 0 {
return dir, r
}
r = next
}
}
func (p *page) all() []*record {
offset := p._indexByFlag2(flag2RecordBegin)
if offset == 0 {
return nil
}
list := make([]*record, 0, 10)
for {
record := p._record(offset)
list = append(list, record)
offset = record.next
if offset == 0 {
break
}
}
return list
}
func (p *page) count() int {
offset := p._indexByFlag2(flag2RecordBegin)
if offset == 0 {
return 0
}
var num = 0
for {
record := p._record(offset)
num++
offset = record.next
if offset == 0 {
break
}
}
return num
}
func (p *page) _indexByFlag2(flag int) uint16 {
return binary.BigEndian.Uint16(p.buf[flag : flag+byte2])
}
func (p *page) _setIndexByFlag2(flag int, value uint16) {
binary.BigEndian.PutUint16(p.buf[flag:flag+byte2], value)
}
func (p *page) _indexByFlag8(flag int) uint64 {
return binary.BigEndian.Uint64(p.buf[flag : flag+byte8])
}
func (p *page) _setIndexByFlag8(flag int, value uint64) {
binary.BigEndian.PutUint64(p.buf[flag:flag+byte8], value)
}
func (p *page) _recordMaxSize() uint16 {
return recordMaxSize(p.size)
}
func (p *page) _reset() {
p._setIndexByFlag2(flag2RecordBegin, 0)
p._setIndexByFlag2(flag2RecycleBegin, 0)
p._setIndexByFlag2(flag2FreeBegin, 0)
p._setIndexByFlag2(flag2DirBegin, 0)
}
// _recycle 回收record空间
func (p *page) _recycle(record *record) {
recycleBegin := p._indexByFlag2(flag2RecycleBegin)
record.next = recycleBegin
p._setRecord(record)
p._setIndexByFlag2(flag2RecycleBegin, record.offset)
}
func (p *page) _setSpace(offset, spaceLen, nextIndex uint16) (uint16, uint16) {
binary.BigEndian.PutUint16(p.buf[offset:], spaceLen)
binary.BigEndian.PutUint16(p.buf[offset+2:], nextIndex)
return offset, offset + spaceLen
}
func (p *page) _getSpace(needSpaceLen uint16) (spaceOffset uint16, spaceLen uint16, ok bool) {
// 从回收空间获取
if spaceOffset, spaceLen, ok = p._getRecycleSpace(needSpaceLen); ok {
return
}
// 熊空闲空间获取
if spaceOffset, spaceLen, ok = p._getFreeSpace(needSpaceLen); ok {
return
}
ok = false
return
}
func (p *page) _getRecycleSpace(needSpaceLen uint16) (spaceOffset uint16, spaceLen uint16, ok bool) {
recycleBegin := p._indexByFlag2(flag2RecycleBegin)
if recycleBegin == 0 {
return 0, 0, false
}
var (
preOffset uint16 = 0
nextIndex uint16 = 0
)
spaceOffset = recycleBegin
for {
// 读取spaceLen
spaceLen = binary.BigEndian.Uint16(p.buf[spaceOffset:])
// 读取nextIndex
nextIndex = binary.BigEndian.Uint16(p.buf[spaceOffset+4:])
if spaceLen >= needSpaceLen {
break
}
if nextIndex == 0 {
return 0, 0, false
}
preOffset = spaceOffset
spaceOffset = nextIndex
}
// 是第一个空闲空间
if preOffset == 0 {
p._setIndexByFlag2(flag2RecycleBegin, nextIndex)
ok = true
return
}
binary.BigEndian.PutUint16(p.buf[preOffset+4:], nextIndex)
ok = true
return
}
func (p *page) _getFreeSpace(needSpaceLen uint16) (spaceOffset uint16, spaceLen uint16, ok bool) {
freeBegin := p._indexByFlag2(flag2FreeBegin)
if freeBegin == 0 {
freeBegin = recordsDefaultBegin
}
dirBegin := p._indexByFlag2(flag2DirBegin)
if dirBegin == 0 {
dirBegin = p.size
}
// 剩余空闲空间检查
if dirBegin-freeBegin < needSpaceLen {
ok = false
return
}
p._setIndexByFlag2(flag2FreeBegin, freeBegin+needSpaceLen)
return freeBegin, needSpaceLen, true
}
// _setRecord 在指定偏移量上设置记录
func (p *page) _setRecord(record *record) {
offset := record.offset
// 设置spaceLen
binary.BigEndian.PutUint16(p.buf[offset:], record.spaceLen)
// 设置pre
offset += 2
binary.BigEndian.PutUint16(p.buf[offset:], record.pre)
// 设置next
offset += 2
binary.BigEndian.PutUint16(p.buf[offset:], record.next)
// 设置keyLen
offset += 2
binary.BigEndian.PutUint16(p.buf[offset:], uint16(len(record.Key)))
// 设置valueLen
offset += 2
binary.BigEndian.PutUint16(p.buf[offset:], uint16(len(record.Value)))
// 设置key
offset += 2
copy(p.buf[offset:], record.Key)
// 设置value
offset += uint16(len(record.Key))
copy(p.buf[offset:], record.Value)
}
// _record 在指定偏移位置
func (p *page) _record(offset uint16) *record {
var record record
record.offset = offset
// 读取spaceLen
record.spaceLen = binary.BigEndian.Uint16(p.buf[offset:])
// 读取pre
offset += 2
record.pre = binary.BigEndian.Uint16(p.buf[offset:])
// 读取next
offset += 2
record.next = binary.BigEndian.Uint16(p.buf[offset:])
// 读取keyLen
offset += 2
keyLen := binary.BigEndian.Uint16(p.buf[offset:])
// 读取valueLen
offset += 2
valueLen := binary.BigEndian.Uint16(p.buf[offset:])
// 读取key
offset += 2
record.Key = make([]byte, keyLen)
copy(record.Key, p.buf[offset:offset+keyLen])
// 读取value
offset += keyLen
record.Value = make([]byte, valueLen)
copy(record.Value, p.buf[offset:offset+valueLen])
record.pageOffset = p.offset
return &record
}
func (p *page) _deleteRecord(r record) {
if r.pre != 0 {
pre := p._record(r.pre)
pre.next = r.next
p._setRecord(pre)
} else {
p._setIndexByFlag2(flag2RecordBegin, r.next)
}
if r.next != 0 {
next := p._record(r.next)
next.pre = r.pre
p._setRecord(next)
}
p._recycle(&r)
}