// LoadSnap opens an index persister which stores pre-built index trees.
// When loading a index snapshot, only the top level of the tree is loaded.
// All other tree branches are loaded only when it's necessary (on request).
func LoadSnap(dir string) (s *Snap, err error) {
segpathr := path.Join(dir, prefixsnaproot)
segpathd := path.Join(dir, prefixsnapdata)
rf, err := segfile.New(segpathr, segszsnap)
if err != nil {
return nil, err
}
root, branches, err := readSnapRoot(rf)
if err != nil {
return nil, err
}
if err := rf.Close(); err != nil {
return nil, err
}
df, err := segfile.New(segpathd, segszsnap)
if err != nil {
return nil, err
}
s = &Snap{
RootNode: root,
branches: branches,
dataFile: df,
}
return s, nil
}
// writeSnapshot creates a snapshot on given path and returns created snapshot.
// This snapshot will have the complete index tree already loaded into ram.
func writeSnapshot(dir string, tree *TNode) (s *Snap, err error) {
segpathr := path.Join(dir, prefixsnaproot)
segpathd := path.Join(dir, prefixsnapdata)
rf, err := segfile.New(segpathr, segszsnap)
if err != nil {
return nil, err
}
// can close this
defer rf.Close()
df, err := segfile.New(segpathd, segszsnap)
if err != nil {
return nil, err
}
brf := bufio.NewWriterSize(rf, 1e7)
bdf := bufio.NewWriterSize(df, 1e7)
branches := map[string]*Offset{}
var offset int64
var buffer []byte
for name, tn := range tree.Children {
size := tn.Size()
sz64 := int64(size)
if len(buffer) < size {
buffer = make([]byte, size)
}
// slice to data size
towrite := buffer[:size]
_, err := tn.MarshalTo(towrite)
if err != nil {
return nil, err
}
for len(towrite) > 0 {
n, err := bdf.Write(towrite)
if err != nil {
return nil, err
}
towrite = towrite[n:]
}
branches[name] = &Offset{offset, offset + sz64}
offset += sz64
}
info := &SnapInfo{
Branches: branches,
}
{
size := info.Size()
sz64 := int64(size)
full := size + hybrid.SzInt64
if len(buffer) < full {
buffer = make([]byte, full)
}
towrite := buffer[:full]
// prepend root info struct size to the buffer
hybrid.EncodeInt64(towrite[:hybrid.SzInt64], &sz64)
_, err := info.MarshalTo(towrite[hybrid.SzInt64:])
if err != nil {
return nil, err
}
for len(towrite) > 0 {
n, err := brf.Write(towrite)
if err != nil {
return nil, err
}
towrite = towrite[n:]
}
}
if err := bdf.Flush(); err != nil {
return nil, err
}
if err := brf.Flush(); err != nil {
return nil, err
}
s = &Snap{
RootNode: tree,
branches: branches,
dataFile: df,
}
return s, nil
}