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disk_wal.go
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disk_wal.go
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package tstorage
import (
"bufio"
"encoding/binary"
"errors"
"fmt"
log "github.com/sirupsen/logrus"
"io"
"io/fs"
"math"
"os"
"path/filepath"
"strconv"
"sync"
"sync/atomic"
)
var corruptedWalRecord = walRecord{
op: corrupted,
row: Row{
Metric: 0,
DataPoint: DataPoint{Timestamp: 0, Value: 0},
}}
// diskWAL contains multiple segment files. One segment is responsible for one partition.
// They can be easily sorted because they are named using the created timestamp.
// Macro layout is like:
/*
.wal/
├── 0
└── 1
*/
type diskWAL struct {
dir string
bufferedSize int
// Buffered-writer to the active segment
w *bufio.Writer
// File descriptor to the active segment
fd *os.File
index uint32
mu sync.Mutex
last map[uint32]*DataPoint
}
func newDiskWAL(dir string, bufferedSize int) (wal, error) {
if err := os.MkdirAll(dir, fs.ModePerm); err != nil {
return nil, fmt.Errorf("failed to make WAL dir: %w", err)
}
w := &diskWAL{
dir: dir,
bufferedSize: bufferedSize,
}
f, err := w.createSegmentFile(dir)
if err != nil {
return nil, err
}
w.fd = f
w.w = bufio.NewWriterSize(f, bufferedSize)
w.last = make(map[uint32]*DataPoint)
return w, nil
}
// append appends the given entry to the end of a file via the file descriptor it has.
func (w *diskWAL) append(op walOperation, rows []Row) error {
w.mu.Lock()
defer w.mu.Unlock()
switch op {
case operationInsert:
for _, row := range rows {
// Write the operation type
if err := w.w.WriteByte(byte(op)); err != nil {
return fmt.Errorf("failed to write operation: %w", err)
}
// Write the metric
mBuf := make([]byte, binary.MaxVarintLen64)
n := binary.PutVarint(mBuf, int64(row.Metric))
if _, err := w.w.Write(mBuf[:n]); err != nil {
return fmt.Errorf("failed to write the metric: %w", err)
}
// Write the timestamp
tsBuf := make([]byte, binary.MaxVarintLen64)
n = binary.PutVarint(tsBuf, row.DataPoint.Timestamp)
if _, err := w.w.Write(tsBuf[:n]); err != nil {
return fmt.Errorf("failed to write the timestamp: %w", err)
}
// Write the value
vBuf := make([]byte, binary.MaxVarintLen64)
n = binary.PutUvarint(vBuf, math.Float64bits(row.DataPoint.Value))
if _, err := w.w.Write(vBuf[:n]); err != nil {
return fmt.Errorf("failed to write the value: %w", err)
}
w.last[row.Metric] = &DataPoint{
Timestamp: row.Timestamp,
Value: row.Value,
}
}
default:
return fmt.Errorf("unknown operation %v given", op)
}
if w.bufferedSize == 0 {
return w.flush()
}
return nil
}
// flush flushes all buffered entries to the underlying file.
func (w *diskWAL) flush() error {
if err := w.w.Flush(); err != nil {
return fmt.Errorf("failed to flush buffered-data into the underlying WAL file: %w", err)
}
return nil
}
// punctuate set boundary and creates a new segment.
func (w *diskWAL) punctuate() error {
w.mu.Lock()
defer w.mu.Unlock()
if err := w.flush(); err != nil {
return err
}
if err := w.fd.Close(); err != nil {
return err
}
f, err := w.createSegmentFile(w.dir)
if err != nil {
return err
}
w.fd = f
w.w = bufio.NewWriterSize(f, w.bufferedSize)
return nil
}
// truncateOldest removes only the oldest segment.
func (w *diskWAL) removeOldest() error {
w.mu.Lock()
defer w.mu.Unlock()
files, err := os.ReadDir(w.dir)
if err != nil {
return fmt.Errorf("failed to read WAL directory: %w", err)
}
if len(files) == 0 {
return fmt.Errorf("no segment found")
}
return os.RemoveAll(filepath.Join(w.dir, files[0].Name()))
}
// removeAll removes all segment files.
func (w *diskWAL) removeAll() error {
w.mu.Lock()
defer w.mu.Unlock()
if err := w.fd.Close(); err != nil {
return err
}
if err := os.RemoveAll(w.dir); err != nil {
return fmt.Errorf("failed to remove files under %q: %w", w.dir, err)
}
return os.MkdirAll(w.dir, fs.ModePerm)
}
// refresh removes all segment files and make a new segment.
func (w *diskWAL) refresh() error {
if err := w.removeAll(); err != nil {
return err
}
w.mu.Lock()
defer w.mu.Unlock()
f, err := w.createSegmentFile(w.dir)
if err != nil {
return err
}
w.fd = f
w.w = bufio.NewWriterSize(f, w.bufferedSize)
return nil
}
// createSegmentFile creates a new file with the name of the numbering index.
func (w *diskWAL) createSegmentFile(dir string) (*os.File, error) {
name := strconv.Itoa(int(atomic.LoadUint32(&w.index)))
f, err := os.OpenFile(filepath.Join(dir, name), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
if err != nil {
return nil, fmt.Errorf("failed to create segment file: %w", err)
}
atomic.AddUint32(&w.index, 1)
return f, nil
}
type walRecord struct {
op walOperation
row Row
}
type diskWALReader struct {
dir string
files []os.DirEntry
rowsToInsert []Row
}
func newDiskWALReader(dir string) (*diskWALReader, error) {
files, err := os.ReadDir(dir)
if err != nil {
return nil, fmt.Errorf("failed to read the WAL dir: %w", err)
}
return &diskWALReader{
dir: dir,
files: files,
rowsToInsert: make([]Row, 0),
}, nil
}
// readAll reads all segment files and caches the result for each operation.
func (f *diskWALReader) readAll(option WalRecoveryOption) error {
for _, file := range f.files {
if file.IsDir() {
return fmt.Errorf("unexpected directory found under the WAL directory: %s", file.Name())
}
fd, err := os.Open(filepath.Join(f.dir, file.Name()))
if err != nil {
return fmt.Errorf("failed to open WAL segment file: %w", err)
}
segment := &segment{
file: fd,
r: bufio.NewReader(fd),
}
for segment.next(option) {
rec := segment.record()
switch rec.op {
case operationInsert:
f.rowsToInsert = append(f.rowsToInsert, rec.row)
}
}
if err := segment.close(); err != nil {
return err
}
err = segment.error()
if err != nil && option == AbsoluteConsistency {
log.Errorf("failed reading WAL with AbsoluteConsistency: %s", err)
return fmt.Errorf("encounter an error while reading WAL segment file %q: %w", file.Name(), segment.error())
}
if errors.Is(err, io.ErrUnexpectedEOF) || errors.Is(err, io.EOF) {
// It is not unusual for a line to be invalid, as it may well terminate in the middle of writing to the WAL.
return nil
}
if err != nil {
log.Errorf("encounter an error while reading WAL segment file %q: %v", file.Name(), segment.error())
if option == SkipAnyCorruptedRecord {
return nil
}
return fmt.Errorf("encounter an error while reading WAL segment file %q: %w", file.Name(), segment.error())
}
}
return nil
}
// segment represents a segment file.
type segment struct {
file *os.File
r *bufio.Reader
// FIXME: Use interface to support other operation type
current walRecord
err error
}
func (f *segment) skipAsCorrupted(err error) bool {
log.Warnf("skipping corrupted wal record: %s", err)
f.current = corruptedWalRecord
return true
}
func (f *segment) next(option WalRecoveryOption) bool {
op, err := f.r.ReadByte()
if errors.Is(err, io.EOF) {
return false
}
if err != nil {
f.err = err
return false
}
switch walOperation(op) {
case operationInsert:
// Read metric
metric, err := binary.ReadVarint(f.r)
if err != nil {
if option == SkipAnyCorruptedRecord {
return f.skipAsCorrupted(err)
} else {
f.err = fmt.Errorf("failed to read metric in wal log: %w", err)
return false
}
}
// Read timestamp
ts, err := binary.ReadVarint(f.r)
if err != nil {
if option == SkipAnyCorruptedRecord {
return f.skipAsCorrupted(err)
} else {
f.err = fmt.Errorf("failed to read timestamp: %w", err)
return false
}
}
// Read value
val, err := binary.ReadUvarint(f.r)
if err != nil {
if option == SkipAnyCorruptedRecord {
return f.skipAsCorrupted(err)
} else {
f.err = fmt.Errorf("failed to read value: %w", err)
return false
}
}
f.current = walRecord{
op: walOperation(op),
row: Row{
Metric: uint32(metric),
DataPoint: DataPoint{
Timestamp: ts,
Value: math.Float64frombits(val),
},
},
}
default:
f.err = fmt.Errorf("unknown operation %v found", op)
return false
}
return true
}
// error gives back an error if it has been facing an error while reading.
func (f *segment) error() error {
return f.err
}
func (f *segment) record() *walRecord {
return &f.current
}
func (f *segment) close() error {
return f.file.Close()
}