save packIDs and duplicates separately
A side remark to the definition of Index.blob: Another possibility would have been to use: blob map[restic.BlobHandle]*indexEntry This would have led to the following sizes: key: 32 + 1 = 33 bytes value: 8 bytes indexEntry: 8 + 4 + 4 = 16 bytes each packID: 32 bytes To save N index entries, we would therefore have needed: N * OF * (33 + 8) bytes + N * 16 + N * 32 bytes / BP = N * 82 bytes More precicely, using a pointer instead of a direct entry is the better memory choice if: OF * 8 bytes + entrysize < OF * entrysize <=> entrysize > 8 bytes * OF/(OF-1) Under the assumption of OF=1.5, this means using pointers would have been the better choice if sizeof(indexEntry) > 24 bytes.
This commit is contained in:
Alexander Weiss
parent
cf979e2b81
commit
ce4a2f4ca6
1 changed files with 106 additions and 70 deletions
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@ -19,27 +19,40 @@ import (
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// Hence the index data structure defined here is one of the main contributions
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// to the total memory requirements of restic.
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//
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// We use a map to store each index entry.
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// We use two maps to store each index entry.
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// The first map stores the first entry of a blobtype/blobID
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// The key of the map is a BlobHandle
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// The entries of the maps are slices which contain the actual index entries.
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// The entries are the actual index entries.
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// In the second map we store duplicate index entries, i.e. entries with same
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// blobtype/blobID
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// In the index entries, we need to reference the packID. As one pack may
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// contain many blobs the packIDs are saved in a separate array and only the index
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// within this array is saved in the indexEntry
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//
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// To compute the needed amount of memory, we need some assumptions.
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// Maps need an overhead of allocated but not needed elements.
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// For computations, we assume an overhead of 50% and use OF=1.5 (overhead factor)
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// As duplicates are only present in edge cases and are also removed by prune runs,
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// we assume that there are no significant duplicates and omit them in the calculations.
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// Moreover we asssume on average a minimum of 8 blobs per pack; BP=8
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// (Note that for large files there should be 3 blobs per pack as the average chunk
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// size is 1.5 MB and the minimum pack size is 4 MB)
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//
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// We have the following sizes:
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// key: 32 + 1 = 33 bytes
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// slice: 24 bytes (pointer, len and cap)
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// indexEntry: 32 + 4 + 4 = 40 bytes
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// indexEntry: 8 + 4 + 4 = 16 bytes
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// each packID: 32 bytes
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//
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// To save N index entries, we therefore need:
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// N * OF * (33 + 24) bytes + N * 40 bytes = N * 126 bytes
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// N * OF * (33 + 16) bytes + N * 32 bytes / BP = N * 78 bytes
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// Index holds a lookup table for id -> pack.
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// Index holds lookup tables for id -> pack.
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type Index struct {
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m sync.Mutex
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pack map[restic.BlobHandle][]indexEntry
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treePacks restic.IDs
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m sync.Mutex
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blob map[restic.BlobHandle]indexEntry
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duplicates map[restic.BlobHandle][]indexEntry
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packs restic.IDs
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treePacks restic.IDs
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final bool // set to true for all indexes read from the backend ("finalized")
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id restic.ID // set to the ID of the index when it's finalized
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@ -48,33 +61,59 @@ type Index struct {
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}
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type indexEntry struct {
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packID restic.ID
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offset uint32
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length uint32
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// only save index do packs; i.e. packs[packindex] yields the packID
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packIndex int
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offset uint32
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length uint32
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}
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// NewIndex returns a new index.
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func NewIndex() *Index {
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return &Index{
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pack: make(map[restic.BlobHandle][]indexEntry),
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created: time.Now(),
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blob: make(map[restic.BlobHandle]indexEntry),
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duplicates: make(map[restic.BlobHandle][]indexEntry),
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created: time.Now(),
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}
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}
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// withDuplicates returns the list of all entries for the given blob handle
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func (idx *Index) withDuplicates(h restic.BlobHandle, entry indexEntry) []indexEntry {
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entries, ok := idx.duplicates[h]
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if ok {
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all := make([]indexEntry, len(entries)+1)
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all[0] = entry
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copy(all[1:], entries)
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return all
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}
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return []indexEntry{entry}
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}
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// addToPacks saves the given pack ID and return the index.
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// This procedere allows to use pack IDs which can be easily garbage collected after.
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func (idx *Index) addToPacks(id restic.ID) int {
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idx.packs = append(idx.packs, id)
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return len(idx.packs) - 1
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}
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const maxuint32 = 1<<32 - 1
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func (idx *Index) store(blob restic.PackedBlob) {
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func (idx *Index) store(packIndex int, blob restic.Blob) {
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// assert that offset and length fit into uint32!
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if blob.Offset > maxuint32 || blob.Length > maxuint32 {
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panic("offset or length does not fit in uint32. You have packs > 4GB!")
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}
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newEntry := indexEntry{
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packID: blob.PackID,
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offset: uint32(blob.Offset),
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length: uint32(blob.Length),
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packIndex: packIndex,
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offset: uint32(blob.Offset),
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length: uint32(blob.Length),
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}
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h := restic.BlobHandle{ID: blob.ID, Type: blob.Type}
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idx.pack[h] = append(idx.pack[h], newEntry)
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if _, ok := idx.blob[h]; ok {
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idx.duplicates[h] = append(idx.duplicates[h], newEntry)
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} else {
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idx.blob[h] = newEntry
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}
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}
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// Final returns true iff the index is already written to the repository, it is
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@ -98,7 +137,7 @@ var IndexFull = func(idx *Index) bool {
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debug.Log("checking whether index %p is full", idx)
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blobs := len(idx.pack)
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blobs := len(idx.blob)
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age := time.Now().Sub(idx.created)
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switch {
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@ -126,7 +165,7 @@ func (idx *Index) Store(blob restic.PackedBlob) {
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debug.Log("%v", blob)
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idx.store(blob)
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idx.store(idx.addToPacks(blob.PackID), blob.Blob)
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}
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// StorePack remembers the ids of all blobs of a given pack
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@ -140,14 +179,15 @@ func (idx *Index) StorePack(id restic.ID, blobs []restic.Blob) {
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}
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debug.Log("%v", blobs)
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packIndex := idx.addToPacks(id)
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for _, blob := range blobs {
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idx.store(restic.PackedBlob{Blob: blob, PackID: id})
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idx.store(packIndex, blob)
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}
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}
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// ListPack returns a list of blobs contained in a pack.
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func indexEntryToPackedBlob(h restic.BlobHandle, entry indexEntry) restic.PackedBlob {
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func (idx *Index) indexEntryToPackedBlob(h restic.BlobHandle, entry indexEntry) restic.PackedBlob {
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return restic.PackedBlob{
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Blob: restic.Blob{
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ID: h.ID,
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@ -155,7 +195,7 @@ func indexEntryToPackedBlob(h restic.BlobHandle, entry indexEntry) restic.Packed
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Length: uint(entry.length),
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Offset: uint(entry.offset),
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},
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PackID: entry.packID,
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PackID: idx.packs[entry.packIndex],
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}
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}
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@ -166,11 +206,13 @@ func (idx *Index) Lookup(id restic.ID, tpe restic.BlobType) (blobs []restic.Pack
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h := restic.BlobHandle{ID: id, Type: tpe}
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if packs, ok := idx.pack[h]; ok {
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blobs = make([]restic.PackedBlob, 0, len(packs))
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blob, ok := idx.blob[h]
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if ok {
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blobList := idx.withDuplicates(h, blob)
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blobs = make([]restic.PackedBlob, 0, len(blobList))
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for _, p := range packs {
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blobs = append(blobs, indexEntryToPackedBlob(h, p))
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for _, p := range blobList {
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blobs = append(blobs, idx.indexEntryToPackedBlob(h, p))
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}
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return blobs, true
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@ -184,10 +226,10 @@ func (idx *Index) ListPack(id restic.ID) (list []restic.PackedBlob) {
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idx.m.Lock()
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defer idx.m.Unlock()
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for h, packList := range idx.pack {
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for _, entry := range packList {
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if entry.packID == id {
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list = append(list, indexEntryToPackedBlob(h, entry))
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for h, entry := range idx.blob {
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for _, blob := range idx.withDuplicates(h, entry) {
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if idx.packs[blob.packIndex] == id {
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list = append(list, idx.indexEntryToPackedBlob(h, blob))
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}
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}
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}
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@ -202,7 +244,7 @@ func (idx *Index) Has(id restic.ID, tpe restic.BlobType) bool {
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h := restic.BlobHandle{ID: id, Type: tpe}
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_, ok := idx.pack[h]
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_, ok := idx.blob[h]
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return ok
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}
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@ -250,12 +292,12 @@ func (idx *Index) Each(ctx context.Context) <-chan restic.PackedBlob {
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close(ch)
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}()
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for h, packs := range idx.pack {
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for _, blob := range packs {
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for h, entry := range idx.blob {
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for _, blob := range idx.withDuplicates(h, entry) {
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select {
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case <-ctx.Done():
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return
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case ch <- indexEntryToPackedBlob(h, blob):
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case ch <- idx.indexEntryToPackedBlob(h, blob):
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}
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}
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}
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@ -270,10 +312,8 @@ func (idx *Index) Packs() restic.IDSet {
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defer idx.m.Unlock()
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packs := restic.NewIDSet()
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for _, list := range idx.pack {
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for _, entry := range list {
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packs.Insert(entry.packID)
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}
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for _, packID := range idx.packs {
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packs.Insert(packID)
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}
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return packs
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@ -285,12 +325,17 @@ func (idx *Index) Count(t restic.BlobType) (n uint) {
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idx.m.Lock()
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defer idx.m.Unlock()
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for h, list := range idx.pack {
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for h := range idx.blob {
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if h.Type != t {
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continue
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}
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n += uint(len(list))
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n++
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}
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for h, dups := range idx.duplicates {
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if h.Type != t {
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continue
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}
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n += uint(len(dups))
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}
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return
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@ -313,25 +358,20 @@ func (idx *Index) generatePackList() ([]*packJSON, error) {
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list := []*packJSON{}
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packs := make(map[restic.ID]*packJSON)
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for h, packedBlobs := range idx.pack {
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for _, blob := range packedBlobs {
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if blob.packID.IsNull() {
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for h, entry := range idx.blob {
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for _, blob := range idx.withDuplicates(h, entry) {
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packID := idx.packs[blob.packIndex]
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if packID.IsNull() {
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panic("null pack id")
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}
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debug.Log("handle blob %v", h)
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if blob.packID.IsNull() {
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debug.Log("blob %v has no packID! (offset %v, length %v)",
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h, blob.offset, blob.length)
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return nil, errors.Errorf("unable to serialize index: pack for blob %v hasn't been written yet", h)
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}
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// see if pack is already in map
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p, ok := packs[blob.packID]
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p, ok := packs[packID]
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if !ok {
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// else create new pack
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p = &packJSON{ID: blob.packID}
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p = &packJSON{ID: packID}
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// and append it to the list and map
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list = append(list, p)
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@ -495,16 +535,14 @@ func DecodeIndex(buf []byte) (idx *Index, err error) {
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idx = NewIndex()
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for _, pack := range idxJSON.Packs {
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var data, tree bool
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packID := idx.addToPacks(pack.ID)
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for _, blob := range pack.Blobs {
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idx.store(restic.PackedBlob{
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Blob: restic.Blob{
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Type: blob.Type,
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ID: blob.ID,
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Offset: blob.Offset,
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Length: blob.Length,
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},
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PackID: pack.ID,
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idx.store(packID, restic.Blob{
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Type: blob.Type,
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ID: blob.ID,
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Offset: blob.Offset,
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Length: blob.Length,
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})
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switch blob.Type {
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@ -540,16 +578,14 @@ func DecodeOldIndex(buf []byte) (idx *Index, err error) {
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idx = NewIndex()
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for _, pack := range list {
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var data, tree bool
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packID := idx.addToPacks(pack.ID)
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for _, blob := range pack.Blobs {
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idx.store(restic.PackedBlob{
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Blob: restic.Blob{
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Type: blob.Type,
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ID: blob.ID,
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Offset: blob.Offset,
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Length: blob.Length,
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},
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PackID: pack.ID,
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idx.store(packID, restic.Blob{
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Type: blob.Type,
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ID: blob.ID,
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Offset: blob.Offset,
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Length: blob.Length,
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})
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switch blob.Type {
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