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entry.go
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entry.go
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package bitcask
import (
"encoding/binary"
"hash/crc32"
"os"
"path/filepath"
)
const (
// UnCommitted represents the tx unCommitted status
UnCommitted uint16 = 0
// Committed represents the tx committed status
Committed uint16 = 1
// Persistent represents the data persistent flag
Persistent uint32 = 0
// ScanNoLimit represents the data scan no limit flag
ScanNoLimit int = -1
)
var (
// DataEntryHeaderSize returns the entry header size
// 数据头的定长部分
DataEntryHeaderSize uint32 = 42
// BucketMetaHeaderSize BucketMeta header size
BucketMetaHeaderSize uint32 = 12
// BucketMetaSuffix B +树索引后缀。
BucketMetaSuffix = ".meta"
)
type (
// Entry 数据item
Entry struct {
Key []byte
Value []byte
Meta *MetaData
crc uint32
position uint64
}
// Hint represents the index of the key
Hint struct {
Key []byte
FileID int64
Meta *MetaData
DataPos uint64
}
// MetaData represents the meta information of the data item.
//表示数据项的元信息。
MetaData struct {
KeySize uint32
ValueSize uint32
Timestamp uint64
TTL uint32
Flag uint16 // delete / set
Bucket []byte
BucketSize uint32
TxID uint64 //committedTxId
Status uint16 // committed / uncommitted
Ds uint16 // data structure
}
// Record 记录 hint 和 entry
Record struct {
H *Hint
E *Entry
}
// BucketMeta represents the bucket's meta-information.
BucketMeta struct {
startSize uint32
endSize uint32
start []byte
end []byte
crc uint32
}
)
// Encode returns the slice after the BucketMeta be encoded.
func (bm *BucketMeta) Encode() []byte {
buf := make([]byte, bm.Size())
binary.LittleEndian.PutUint32(buf[4:8], bm.startSize)
binary.LittleEndian.PutUint32(buf[8:12], bm.endSize)
startBuf := buf[BucketMetaHeaderSize:(BucketMetaHeaderSize + bm.startSize)]
copy(startBuf, bm.start)
endBuf := buf[BucketMetaHeaderSize+bm.startSize : (BucketMetaHeaderSize + bm.startSize + bm.endSize)]
copy(endBuf, bm.end)
c32 := crc32.ChecksumIEEE(buf[4:])
binary.LittleEndian.PutUint32(buf[0:4], c32)
return buf
}
// GetCrc returns the crc at given buf slice.
func (bm *BucketMeta) GetCrc(buf []byte) uint32 {
crc := crc32.ChecksumIEEE(buf[4:])
crc = crc32.Update(crc, crc32.IEEETable, bm.start)
crc = crc32.Update(crc, crc32.IEEETable, bm.end)
return crc
}
// Size returns the size of the BucketMeta.
func (bm *BucketMeta) Size() int64 {
return int64(BucketMetaHeaderSize + bm.startSize + bm.endSize)
}
/*Entry*/
//IsZero 检查 entry 是否为0
//这里是否能有一个字段判断即可
func (e *Entry) IsZero() bool {
if e.crc == 0 && e.Meta.KeySize == 0 && e.Meta.ValueSize == 0 && e.Meta.Timestamp == 0 {
return true
}
return false
}
//GetCrc returns the crc at given buf slice.
//返回给定buf片的CRC。
func (e *Entry) GetCrc(buf []byte) uint32 {
crc := crc32.ChecksumIEEE(buf[4:])
crc = crc32.Update(crc, crc32.IEEETable, e.Meta.Bucket)
crc = crc32.Update(crc, crc32.IEEETable, e.Key)
crc = crc32.Update(crc, crc32.IEEETable, e.Value)
return crc
}
//Size entry 的数据大小
func (e *Entry) Size() int64 {
return int64(uint32(DataEntryHeaderSize) + e.Meta.KeySize + e.Meta.ValueSize + e.Meta.BucketSize)
}
// Encode returns the slice after the entry be encoded.
//
// the entry stored format:
// |----------------------------------------------------------------------------------------------------------------|
// | crc | timestamp | ksz | valueSize | flag | TTL |bucketSize| status | ds | txId | bucket | key | value |
// |----------------------------------------------------------------------------------------------------------------|
// | uint32| uint64 |uint32 | uint32 | uint16 | uint32| uint32 | uint16 | uint16 |uint64 |[]byte|[]byte | []byte |
// |----------------------------------------------------------------------------------------------------------------|
//
func (e *Entry) Encode() []byte {
keySize := e.Meta.KeySize
valueSize := e.Meta.ValueSize
bucketSize := e.Meta.BucketSize
//set DataItemHeader buf
buf := make([]byte, e.Size())
buf = e.setEntryHeaderBuf(buf)
//set bucket\key\value
copy(buf[DataEntryHeaderSize:(bucketSize+DataEntryHeaderSize)], e.Meta.Bucket)
copy(buf[(DataEntryHeaderSize+bucketSize):(DataEntryHeaderSize+bucketSize+keySize)], e.Key)
copy(buf[(DataEntryHeaderSize+bucketSize+keySize):(DataEntryHeaderSize+bucketSize+keySize+valueSize)], e.Value)
c32 := crc32.ChecksumIEEE(buf[4:])
binary.LittleEndian.PutUint32(buf[0:4], c32)
return buf
}
// setEntryHeaderBuf sets the entry header buff.
func (e *Entry) setEntryHeaderBuf(buf []byte) []byte {
binary.LittleEndian.PutUint64(buf[4:12], e.Meta.Timestamp)
binary.LittleEndian.PutUint32(buf[12:16], e.Meta.KeySize)
binary.LittleEndian.PutUint32(buf[16:20], e.Meta.ValueSize)
binary.LittleEndian.PutUint16(buf[20:22], e.Meta.Flag)
binary.LittleEndian.PutUint32(buf[22:26], e.Meta.TTL)
binary.LittleEndian.PutUint32(buf[26:30], e.Meta.BucketSize)
binary.LittleEndian.PutUint16(buf[30:32], e.Meta.Status)
binary.LittleEndian.PutUint16(buf[32:34], e.Meta.Ds)
binary.LittleEndian.PutUint64(buf[34:42], e.Meta.TxID)
return buf
}
// MetaDataDecode 根据buffer 构建 metadata 元数据结构
// 定长部分会进行crc校验
// crc, timestamp,key_size,value_size,flag,ttl,bucket_size,status,data_structure,tx_id
func MetaDataDecode(buf []byte) *MetaData {
return &MetaData{
Timestamp: binary.LittleEndian.Uint64(buf[4:12]),
KeySize: binary.LittleEndian.Uint32(buf[12:16]),
ValueSize: binary.LittleEndian.Uint32(buf[16:20]),
Flag: binary.LittleEndian.Uint16(buf[20:22]),
TTL: binary.LittleEndian.Uint32(buf[22:26]),
BucketSize: binary.LittleEndian.Uint32(buf[26:30]),
Status: binary.LittleEndian.Uint16(buf[30:32]),
Ds: binary.LittleEndian.Uint16(buf[32:34]),
TxID: binary.LittleEndian.Uint64(buf[34:42]),
}
}
/*BucketMeta*/
// ReadBucketMetaFromPath bucketMeta 解码
func ReadBucketMetaFromPath(path string) (bucketMeta *BucketMeta, err error) {
//open File
fd, err := os.OpenFile(filepath.Clean(path), os.O_CREATE|os.O_RDWR, 0644)
if err != nil {
return
}
defer fd.Close()
var off int64
//读取数据 BucketMeta
headerBuff := make([]byte, BucketMetaHeaderSize)
_, err = fd.ReadAt(headerBuff, off)
if err != nil {
return
}
// 将header 解码为 crc ,startSize,endSize
startSize := binary.LittleEndian.Uint32(headerBuff[4:8])
endSize := binary.LittleEndian.Uint32(headerBuff[8:12])
bucketMeta = &BucketMeta{
startSize: startSize,
endSize: endSize,
crc: binary.LittleEndian.Uint32(headerBuff[0:4]),
}
//读取变长部分
//1.读取 start
off += int64(BucketMetaHeaderSize) // 跳过已经读取的 header 部分
startBuf := make([]byte, startSize)
if _, err = fd.ReadAt(startBuf, off); err != nil {
return nil, err
}
bucketMeta.start = startBuf
// 2.读取 end
off += int64(startSize) // 跳过已经读取的 start 部分
endBuf := make([]byte, endSize)
if _, err = fd.ReadAt(endBuf, off); err != nil {
return nil, err
}
bucketMeta.end = endBuf
//crc32 校验
if bucketMeta.GetCrc(headerBuff) != bucketMeta.crc {
return nil, ErrCrc
}
return
}
// UpdateRecord updates the record.
func (r *Record) UpdateRecord(h *Hint, e *Entry) error {
r.E = e
r.H = h
return nil
}
// IsExpired returns the record if expired or not.
func (r *Record) IsExpired() bool {
return IsExpired(r.H.Meta.TTL, r.H.Meta.Timestamp)
}