// Create creates a WAL ready for appending records. The given metadata is
// recorded at the head of each WAL file, and can be retrieved with ReadAll.
func Create(dirpath string, metadata []byte) (*WAL, error) {
if Exist(dirpath) {
return nil, os.ErrExist
}
if err := os.MkdirAll(dirpath, privateDirMode); err != nil {
return nil, err
}
p := path.Join(dirpath, walName(0, 0))
f, err := os.OpenFile(p, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0600)
if err != nil {
return nil, err
}
l, err := fileutil.NewLock(f.Name())
if err != nil {
return nil, err
}
if err = l.Lock(); err != nil {
return nil, err
}
w := &WAL{
dir: dirpath,
metadata: metadata,
seq: 0,
f: f,
encoder: newEncoder(f, 0),
}
w.locks = append(w.locks, l)
if err := w.saveCrc(0); err != nil {
return nil, err
}
if err := w.encoder.encode(&walpb.Record{Type: metadataType, Data: metadata}); err != nil {
return nil, err
}
if err := w.SaveSnapshot(walpb.Snapshot{}); err != nil {
return nil, err
}
return w, nil
}
// cut closes current file written and creates a new one ready to append.
// cut first creates a temp wal file and writes necessary headers into it.
// Then cut atomically rename temp wal file to a wal file.
func (w *WAL) cut() error {
// close old wal file
if err := w.sync(); err != nil {
return err
}
if err := w.f.Close(); err != nil {
return err
}
fpath := path.Join(w.dir, walName(w.seq+1, w.enti+1))
ftpath := fpath + ".tmp"
// create a temp wal file with name sequence + 1, or truncate the existing one
ft, err := os.OpenFile(ftpath, os.O_WRONLY|os.O_APPEND|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
return err
}
// update writer and save the previous crc
w.f = ft
prevCrc := w.encoder.crc.Sum32()
w.encoder = newEncoder(w.f, prevCrc)
if err = w.saveCrc(prevCrc); err != nil {
return err
}
if err = w.encoder.encode(&walpb.Record{Type: metadataType, Data: w.metadata}); err != nil {
return err
}
if err = w.saveState(&w.state); err != nil {
return err
}
// close temp wal file
if err = w.sync(); err != nil {
return err
}
if err = w.f.Close(); err != nil {
return err
}
// atomically move temp wal file to wal file
if err = os.Rename(ftpath, fpath); err != nil {
return err
}
// open the wal file and update writer again
f, err := os.OpenFile(fpath, os.O_WRONLY|os.O_APPEND, 0600)
if err != nil {
return err
}
if err = fileutil.Preallocate(f, segmentSizeBytes); err != nil {
plog.Errorf("failed to allocate space when creating new wal file (%v)", err)
return err
}
w.f = f
prevCrc = w.encoder.crc.Sum32()
w.encoder = newEncoder(w.f, prevCrc)
// lock the new wal file
l, err := fileutil.NewLock(f.Name())
if err != nil {
return err
}
if err := l.Lock(); err != nil {
return err
}
w.locks = append(w.locks, l)
// increase the wal seq
w.seq++
plog.Infof("segmented wal file %v is created", fpath)
return nil
}
func openAtIndex(dirpath string, snap walpb.Snapshot, write bool) (*WAL, error) {
names, err := fileutil.ReadDir(dirpath)
if err != nil {
return nil, err
}
names = checkWalNames(names)
if len(names) == 0 {
return nil, ErrFileNotFound
}
nameIndex, ok := searchIndex(names, snap.Index)
if !ok || !isValidSeq(names[nameIndex:]) {
return nil, ErrFileNotFound
}
// open the wal files for reading
rcs := make([]io.ReadCloser, 0)
ls := make([]fileutil.Lock, 0)
for _, name := range names[nameIndex:] {
f, err := os.Open(path.Join(dirpath, name))
if err != nil {
return nil, err
}
l, err := fileutil.NewLock(f.Name())
if err != nil {
return nil, err
}
err = l.TryLock()
if err != nil {
if write {
return nil, err
}
}
rcs = append(rcs, f)
ls = append(ls, l)
}
rc := MultiReadCloser(rcs...)
// create a WAL ready for reading
w := &WAL{
dir: dirpath,
start: snap,
decoder: newDecoder(rc),
locks: ls,
}
if write {
// open the last wal file for appending
seq, _, err := parseWalName(names[len(names)-1])
if err != nil {
rc.Close()
return nil, err
}
last := path.Join(dirpath, names[len(names)-1])
f, err := os.OpenFile(last, os.O_WRONLY|os.O_APPEND, 0)
if err != nil {
rc.Close()
return nil, err
}
err = fileutil.Preallocate(f, segmentSizeBytes)
if err != nil {
rc.Close()
plog.Errorf("failed to allocate space when creating new wal file (%v)", err)
return nil, err
}
w.f = f
w.seq = seq
}
return w, nil
}