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mirror of https://github.com/octoleo/restic.git synced 2024-12-23 03:18:55 +00:00
restic/internal/restorer/filerestorer.go
Michael Eischer c147422ba5 repository: special case SaveBlob for all zero chunks
Sparse files contain large regions containing only zero bytes. Checking
that a blob only contains zeros is possible with over 100GB/s for modern
x86 CPUs. Calculating sha256 hashes is only possible with 500MB/s (or
2GB/s using hardware acceleration). Thus we can speed up the hash
calculation for all zero blobs (which always have length
chunker.MinSize) by checking for zero bytes and then using the
precomputed hash.

The all zeros check is only performed for blobs with the minimal chunk
size, and thus should add no overhead most of the time. For chunks which
are not all zero but have the minimal chunks size, the overhead will be
below 2% based on the above performance numbers.

This allows reading sparse sections of files as fast as the kernel can
return data to us. On my system using BTRFS this resulted in about
4GB/s.
2022-09-24 21:39:39 +02:00

292 lines
7.7 KiB
Go

package restorer
import (
"context"
"path/filepath"
"sync"
"golang.org/x/sync/errgroup"
"github.com/restic/restic/internal/crypto"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/errors"
"github.com/restic/restic/internal/repository"
"github.com/restic/restic/internal/restic"
)
// TODO if a blob is corrupt, there may be good blob copies in other packs
// TODO evaluate if it makes sense to split download and processing workers
// pro: can (slowly) read network and decrypt/write files concurrently
// con: each worker needs to keep one pack in memory
const (
largeFileBlobCount = 25
)
// information about regular file being restored
type fileInfo struct {
lock sync.Mutex
inProgress bool
sparse bool
size int64
location string // file on local filesystem relative to restorer basedir
blobs interface{} // blobs of the file
}
type fileBlobInfo struct {
id restic.ID // the blob id
offset int64 // blob offset in the file
}
// information about a data pack required to restore one or more files
type packInfo struct {
id restic.ID // the pack id
files map[*fileInfo]struct{} // set of files that use blobs from this pack
}
// fileRestorer restores set of files
type fileRestorer struct {
key *crypto.Key
idx func(restic.BlobHandle) []restic.PackedBlob
packLoader repository.BackendLoadFn
workerCount int
filesWriter *filesWriter
zeroChunk restic.ID
sparse bool
dst string
files []*fileInfo
Error func(string, error) error
}
func newFileRestorer(dst string,
packLoader repository.BackendLoadFn,
key *crypto.Key,
idx func(restic.BlobHandle) []restic.PackedBlob,
connections uint,
sparse bool) *fileRestorer {
// as packs are streamed the concurrency is limited by IO
workerCount := int(connections)
return &fileRestorer{
key: key,
idx: idx,
packLoader: packLoader,
filesWriter: newFilesWriter(workerCount),
zeroChunk: repository.ZeroChunk(),
sparse: sparse,
workerCount: workerCount,
dst: dst,
Error: restorerAbortOnAllErrors,
}
}
func (r *fileRestorer) addFile(location string, content restic.IDs, size int64) {
r.files = append(r.files, &fileInfo{location: location, blobs: content, size: size})
}
func (r *fileRestorer) targetPath(location string) string {
return filepath.Join(r.dst, location)
}
func (r *fileRestorer) forEachBlob(blobIDs []restic.ID, fn func(packID restic.ID, packBlob restic.Blob)) error {
if len(blobIDs) == 0 {
return nil
}
for _, blobID := range blobIDs {
packs := r.idx(restic.BlobHandle{ID: blobID, Type: restic.DataBlob})
if len(packs) == 0 {
return errors.Errorf("Unknown blob %s", blobID.String())
}
fn(packs[0].PackID, packs[0].Blob)
}
return nil
}
func (r *fileRestorer) restoreFiles(ctx context.Context) error {
packs := make(map[restic.ID]*packInfo) // all packs
// Process packs in order of first access. While this cannot guarantee
// that file chunks are restored sequentially, it offers a good enough
// approximation to shorten restore times by up to 19% in some test.
var packOrder restic.IDs
// create packInfo from fileInfo
for _, file := range r.files {
fileBlobs := file.blobs.(restic.IDs)
largeFile := len(fileBlobs) > largeFileBlobCount
var packsMap map[restic.ID][]fileBlobInfo
if largeFile {
packsMap = make(map[restic.ID][]fileBlobInfo)
}
fileOffset := int64(0)
err := r.forEachBlob(fileBlobs, func(packID restic.ID, blob restic.Blob) {
if largeFile {
packsMap[packID] = append(packsMap[packID], fileBlobInfo{id: blob.ID, offset: fileOffset})
fileOffset += int64(blob.DataLength())
}
pack, ok := packs[packID]
if !ok {
pack = &packInfo{
id: packID,
files: make(map[*fileInfo]struct{}),
}
packs[packID] = pack
packOrder = append(packOrder, packID)
}
pack.files[file] = struct{}{}
if blob.ID.Equal(r.zeroChunk) {
file.sparse = r.sparse
}
})
if len(fileBlobs) == 1 {
// no need to preallocate files with a single block, thus we can always consider them to be sparse
// in addition, a short chunk will never match r.zeroChunk which would prevent sparseness for short files
file.sparse = r.sparse
}
if err != nil {
// repository index is messed up, can't do anything
return err
}
if largeFile {
file.blobs = packsMap
}
}
wg, ctx := errgroup.WithContext(ctx)
downloadCh := make(chan *packInfo)
worker := func() error {
for pack := range downloadCh {
if err := r.downloadPack(ctx, pack); err != nil {
return err
}
}
return nil
}
for i := 0; i < r.workerCount; i++ {
wg.Go(worker)
}
// the main restore loop
wg.Go(func() error {
for _, id := range packOrder {
pack := packs[id]
select {
case <-ctx.Done():
return ctx.Err()
case downloadCh <- pack:
debug.Log("Scheduled download pack %s", pack.id.Str())
}
}
close(downloadCh)
return nil
})
return wg.Wait()
}
func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
// calculate blob->[]files->[]offsets mappings
blobs := make(map[restic.ID]struct {
files map[*fileInfo][]int64 // file -> offsets (plural!) of the blob in the file
})
var blobList []restic.Blob
for file := range pack.files {
addBlob := func(blob restic.Blob, fileOffset int64) {
blobInfo, ok := blobs[blob.ID]
if !ok {
blobInfo.files = make(map[*fileInfo][]int64)
blobList = append(blobList, blob)
blobs[blob.ID] = blobInfo
}
blobInfo.files[file] = append(blobInfo.files[file], fileOffset)
}
if fileBlobs, ok := file.blobs.(restic.IDs); ok {
fileOffset := int64(0)
err := r.forEachBlob(fileBlobs, func(packID restic.ID, blob restic.Blob) {
if packID.Equal(pack.id) {
addBlob(blob, fileOffset)
}
fileOffset += int64(blob.DataLength())
})
if err != nil {
// restoreFiles should have caught this error before
panic(err)
}
} else if packsMap, ok := file.blobs.(map[restic.ID][]fileBlobInfo); ok {
for _, blob := range packsMap[pack.id] {
idxPacks := r.idx(restic.BlobHandle{ID: blob.id, Type: restic.DataBlob})
for _, idxPack := range idxPacks {
if idxPack.PackID.Equal(pack.id) {
addBlob(idxPack.Blob, blob.offset)
break
}
}
}
}
}
sanitizeError := func(file *fileInfo, err error) error {
if err != nil {
err = r.Error(file.location, err)
}
return err
}
err := repository.StreamPack(ctx, r.packLoader, r.key, pack.id, blobList, func(h restic.BlobHandle, blobData []byte, err error) error {
blob := blobs[h.ID]
if err != nil {
for file := range blob.files {
if errFile := sanitizeError(file, err); errFile != nil {
return errFile
}
}
return nil
}
for file, offsets := range blob.files {
for _, offset := range offsets {
writeToFile := func() error {
// this looks overly complicated and needs explanation
// two competing requirements:
// - must create the file once and only once
// - should allow concurrent writes to the file
// so write the first blob while holding file lock
// write other blobs after releasing the lock
createSize := int64(-1)
file.lock.Lock()
if file.inProgress {
file.lock.Unlock()
} else {
defer file.lock.Unlock()
file.inProgress = true
createSize = file.size
}
return r.filesWriter.writeToFile(r.targetPath(file.location), blobData, offset, createSize, file.sparse)
}
err := sanitizeError(file, writeToFile())
if err != nil {
return err
}
}
}
return nil
})
if err != nil {
for file := range pack.files {
if errFile := sanitizeError(file, err); errFile != nil {
return errFile
}
}
}
return nil
}