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slab.go
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slab.go
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package gomap
import (
"encoding/binary"
"fmt"
"log"
"os"
"github.com/edsrzf/mmap-go"
"github.com/go-errors/errors"
"golang.org/x/sys/unix"
)
func (h *Hashmap) writeSlab(buf []byte) {
_, err := h.realSlabFILE.Write(buf) // Write the buffer to the file
if err != nil {
panic(err)
}
}
// ReadBytes reads N bytes from a given offset in the file
func (h *Hashmap) ReadBytes(offset SlabOffset, n int64) ([]byte, error) {
bytes := make([]byte, n)
_, err := h.realSlabFILE.ReadAt(bytes, int64(offset))
if err != nil {
return nil, err
}
return bytes, nil
}
func (h *Hashmap) addSlab(item Item) Key {
offset := *h.slabOffset
key := item.Key
val := item.Value
keylen := len(key)
vallen := len(val)
actualTotalLength := 16 + keylen + vallen
if cap(h.slabData) < actualTotalLength {
h.slabData = make([]byte, 0, actualTotalLength)
} else {
h.slabData = h.slabData[:0]
} // Write key length
h.slabData = append(h.slabData, encodeuint64(uint64(keylen))...)
h.slabData = append(h.slabData, encodeuint64(uint64(vallen))...)
h.slabData = append(h.slabData, key...)
h.slabData = append(h.slabData, val...)
h.writeSlab(h.slabData)
*h.slabOffset += SlabOffset(actualTotalLength)
ret := Key{slabOffset: offset, hash: hash(key)} // todo only actually compute hash() once
return ret
}
func (h *Hashmap) addManySlabs(items []Item) []Key {
slabOffsets := make([]Key, len(items))
if cap(h.slabData) < len(items)*2048 {
h.slabData = make([]byte, 0, len(items)*2048)
} else {
h.slabData = h.slabData[:0]
}
offset := *h.slabOffset
for i, item := range items {
keyBytes := item.Key
valueBytes := item.Value
totalLength := len(keyBytes) + len(valueBytes) + 16 // 10 is the maximum length of LEB128 encoded uint64
slabOffsets[i] = Key{slabOffset: offset, hash: hash(keyBytes)} // todo only actually compute hash() once
// Write key length
h.slabData = append(h.slabData, encodeuint64(uint64(len(keyBytes)))...)
h.slabData = append(h.slabData, encodeuint64(uint64(len(valueBytes)))...)
h.slabData = append(h.slabData, keyBytes...)
h.slabData = append(h.slabData, valueBytes...)
offset += SlabOffset(totalLength)
}
h.writeSlab(h.slabData)
*h.slabOffset += SlabOffset(len(h.slabData))
return slabOffsets
}
func (h *Hashmap) unmarshalItemFromSlab(slabValues Key) Item {
var ret Item
headerBytes, err := h.ReadBytes(slabValues.slabOffset, int64(16))
if err != nil {
fmt.Println("slabValues", slabValues)
panic(err)
}
keyLength, _ := decodeuint64(headerBytes[0:8])
valueLength, _ := decodeuint64(headerBytes[8:16])
valuesBytes, err := h.ReadBytes(slabValues.slabOffset+16, int64(keyLength+valueLength))
if err != nil {
panic(err)
}
ret.Key = valuesBytes[0:keyLength]
ret.Value = valuesBytes[keyLength:]
return ret
}
func decodeuint64(input []byte) (uint64, int) {
return binary.LittleEndian.Uint64(input), 8
}
func encodeuint64(input uint64) []byte {
ret := make([]byte, 8)
binary.LittleEndian.PutUint64(ret, input)
return ret
}
func encodeLEB128(slab []byte, input uint64) int {
var i int
for input >= 0x80 {
slab[i] = byte(input&0x7F | 0x80)
input >>= 7
i++
}
slab[i] = byte(input)
return i + 1
}
func decodeLEB128(input []byte) (uint64, int) {
var result uint64
var shift uint
var length int
for {
b := input[length]
length++
result |= (uint64(b&0x7F) << shift)
if b&0x80 == 0 {
break
}
shift += 7
}
return result, length
}
func (h *Hashmap) openMmapSlab(slabSize int64) (mmap.MMap, *os.File, error) {
var f *os.File
var err error
err = os.MkdirAll(h.Folder, 0755)
if err != nil {
log.Fatal("1", h.Folder, "2", errors.Wrap(err, 1))
}
filename := h.Folder + "/slab"
realfilename := filename + "-real"
if !doesFileExist(realfilename) {
_, _ = os.Create(realfilename)
}
fmt.Println(realfilename)
file, err := os.OpenFile(realfilename, os.O_RDWR|os.O_APPEND, 0644)
if err != nil {
log.Fatal("2", errors.Wrap(err, 1))
}
h.realSlabFILE = file
if !doesFileExist(filename) {
f, err = os.Create(filename)
if err != nil {
log.Fatal("2", errors.Wrap(err, 1))
}
f.Seek(slabSize-1, 0)
f.Write([]byte("\x00"))
f.Seek(0, 0)
f.Sync()
f.Close()
}
f, err = os.OpenFile(filename, os.O_RDWR, 0655)
//todo test:
// f, err = os.OpenFile(filename, os.O_RDWR|os.O_SYNC, 0655)
if err != nil {
log.Fatal("3", errors.Wrap(err, 1))
}
fi, err := f.Stat()
if err != nil {
log.Fatal("4", errors.Wrap(err, 1))
}
if slabSize > fi.Size() { // need to expand file
f.Seek(slabSize-1, 0)
f.Write([]byte("\x00"))
f.Seek(0, 0)
f.Sync()
}
// Advise the kernel that we intend to access the file sequentially.
// This will enable the kernel to do read-ahead and improve write performance.
if err := unix.Fadvise(int(f.Fd()), 0, int64(fi.Size()), unix.FADV_SEQUENTIAL); err != nil {
f.Close()
return nil, nil, fmt.Errorf("failed to advise kernel for file %s: %w", filename, err)
}
// mmap the whole file into memory with read-write permissions.
// As the file is larger than memory, it won't be fully loaded into memory.
// Instead, the kernel will load and unload parts of the file as needed.
ret, err := unix.Mmap(int(f.Fd()), 0, int(fi.Size()), unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
if err != nil {
f.Close()
return nil, nil, fmt.Errorf("failed to mmap file %s: %w", filename, err)
}
// Advise the kernel that the mapped memory will be accessed soon.
// This will help to reduce the number of page faults in the beginning of the processing.
if err := unix.Madvise(ret, unix.MADV_WILLNEED); err != nil {
unix.Munmap(ret)
f.Close()
return nil, nil, fmt.Errorf("failed to advise kernel for file %s: %w", filename, err)
}
return ret, f, err
}
func (h *Hashmap) doubleSlab() error {
f := h.slabFILE
f.Seek(2*h.slabSize-1, 0)
f.Write([]byte("\x00"))
f.Seek(0, 0)
f.Sync()
m, err := mmap.Map(f, mmap.RDWR, 0)
if err != nil {
return err
}
h.slabSize *= 2
h.slabMap = m
return nil
}