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Merge pull request #2781 from aawsome/reduce-index-memory

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Reduce index memory
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MichaelEischer 2020-06-14 10:58:28 +02:00 committed by GitHub
commit 74bc7141c1
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4 changed files with 174 additions and 112 deletions
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6
changelog/unreleased/pull-2781 Normal file
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@ -0,0 +1,6 @@
Enhancement: Reduce memory consumption of in-memory index
We've improved how the index is stored in memory.
This change reduces memory usage for large repositories by about 30-40%.
https://github.com/restic/restic/pull/2781

245
internal/repository/index.go
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@ -13,11 +13,48 @@ import (
"github.com/restic/restic/internal/debug"
)
// Index holds a lookup table for id -> pack.
// In large repositories, millions of blobs are stored in the repository
// and restic needs to store an index entry for each blob in memory for
// most operations.
// Hence the index data structure defined here is one of the main contributions
// to the total memory requirements of restic.
//
// We use two maps to store each index entry.
// The first map stores the first entry of a blobtype/blobID
// The key of the map is a BlobHandle
// The entries are the actual index entries.
// In the second map we store duplicate index entries, i.e. entries with same
// blobtype/blobID
// In the index entries, we need to reference the packID. As one pack may
// contain many blobs the packIDs are saved in a separate array and only the index
// within this array is saved in the indexEntry
//
// To compute the needed amount of memory, we need some assumptions.
// Maps need an overhead of allocated but not needed elements.
// For computations, we assume an overhead of 50% and use OF=1.5 (overhead factor)
// As duplicates are only present in edge cases and are also removed by prune runs,
// we assume that there are no significant duplicates and omit them in the calculations.
// Moreover we asssume on average a minimum of 8 blobs per pack; BP=8
// (Note that for large files there should be 3 blobs per pack as the average chunk
// size is 1.5 MB and the minimum pack size is 4 MB)
//
// We have the following sizes:
// key: 32 + 1 = 33 bytes
// indexEntry: 8 + 4 + 4 = 16 bytes
// each packID: 32 bytes
//
// To save N index entries, we therefore need:
// N * OF * (33 + 16) bytes + N * 32 bytes / BP = N * 78 bytes
// Index holds lookup tables for id -> pack.
type Index struct {
m sync.Mutex
pack map[restic.BlobHandle][]indexEntry
treePacks restic.IDs
m sync.Mutex
blob map[restic.BlobHandle]indexEntry
duplicates map[restic.BlobHandle][]indexEntry
packs restic.IDs
treePacks restic.IDs
// only used by Store, StorePacks does not check for already saved packIDs
packIDToIndex map[restic.ID]int
final bool // set to true for all indexes read from the backend ("finalized")
id restic.ID // set to the ID of the index when it's finalized
@ -26,27 +63,60 @@ type Index struct {
}
type indexEntry struct {
packID restic.ID
offset uint
length uint
// only save index do packs; i.e. packs[packindex] yields the packID
packIndex int
offset uint32
length uint32
}
// NewIndex returns a new index.
func NewIndex() *Index {
return &Index{
pack: make(map[restic.BlobHandle][]indexEntry),
created: time.Now(),
blob: make(map[restic.BlobHandle]indexEntry),
duplicates: make(map[restic.BlobHandle][]indexEntry),
packIDToIndex: make(map[restic.ID]int),
created: time.Now(),
}
}
func (idx *Index) store(blob restic.PackedBlob) {
// withDuplicates returns the list of all entries for the given blob handle
func (idx *Index) withDuplicates(h restic.BlobHandle, entry indexEntry) []indexEntry {
entries, ok := idx.duplicates[h]
if ok {
all := make([]indexEntry, len(entries)+1)
all[0] = entry
copy(all[1:], entries)
return all
}
return []indexEntry{entry}
}
// addToPacks saves the given pack ID and return the index.
// This procedere allows to use pack IDs which can be easily garbage collected after.
func (idx *Index) addToPacks(id restic.ID) int {
idx.packs = append(idx.packs, id)
return len(idx.packs) - 1
}
const maxuint32 = 1<<32 - 1
func (idx *Index) store(packIndex int, blob restic.Blob) {
// assert that offset and length fit into uint32!
if blob.Offset > maxuint32 || blob.Length > maxuint32 {
panic("offset or length does not fit in uint32. You have packs > 4GB!")
}
newEntry := indexEntry{
packID: blob.PackID,
offset: blob.Offset,
length: blob.Length,
packIndex: packIndex,
offset: uint32(blob.Offset),
length: uint32(blob.Length),
}
h := restic.BlobHandle{ID: blob.ID, Type: blob.Type}
idx.pack[h] = append(idx.pack[h], newEntry)
if _, ok := idx.blob[h]; ok {
idx.duplicates[h] = append(idx.duplicates[h], newEntry)
} else {
idx.blob[h] = newEntry
}
}
// Final returns true iff the index is already written to the repository, it is
@ -70,7 +140,7 @@ var IndexFull = func(idx *Index) bool {
debug.Log("checking whether index %p is full", idx)
blobs := len(idx.pack)
blobs := len(idx.blob)
age := time.Now().Sub(idx.created)
switch {
@ -98,7 +168,14 @@ func (idx *Index) Store(blob restic.PackedBlob) {
debug.Log("%v", blob)
idx.store(blob)
// get packIndex and save if new packID
packIndex, ok := idx.packIDToIndex[blob.PackID]
if !ok {
packIndex = idx.addToPacks(blob.PackID)
idx.packIDToIndex[blob.PackID] = packIndex
}
idx.store(packIndex, blob.Blob)
}
// StorePack remembers the ids of all blobs of a given pack
@ -112,9 +189,23 @@ func (idx *Index) StorePack(id restic.ID, blobs []restic.Blob) {
}
debug.Log("%v", blobs)
packIndex := idx.addToPacks(id)
for _, blob := range blobs {
idx.store(restic.PackedBlob{Blob: blob, PackID: id})
idx.store(packIndex, blob)
}
}
// ListPack returns a list of blobs contained in a pack.
func (idx *Index) indexEntryToPackedBlob(h restic.BlobHandle, entry indexEntry) restic.PackedBlob {
return restic.PackedBlob{
Blob: restic.Blob{
ID: h.ID,
Type: h.Type,
Length: uint(entry.length),
Offset: uint(entry.offset),
},
PackID: idx.packs[entry.packIndex],
}
}
@ -125,21 +216,13 @@ func (idx *Index) Lookup(id restic.ID, tpe restic.BlobType) (blobs []restic.Pack
h := restic.BlobHandle{ID: id, Type: tpe}
if packs, ok := idx.pack[h]; ok {
blobs = make([]restic.PackedBlob, 0, len(packs))
blob, ok := idx.blob[h]
if ok {
blobList := idx.withDuplicates(h, blob)
blobs = make([]restic.PackedBlob, 0, len(blobList))
for _, p := range packs {
blob := restic.PackedBlob{
Blob: restic.Blob{
Type: tpe,
Length: p.length,
ID: id,
Offset: p.offset,
},
PackID: p.packID,
}
blobs = append(blobs, blob)
for _, p := range blobList {
blobs = append(blobs, idx.indexEntryToPackedBlob(h, p))
}
return blobs, true
@ -153,18 +236,10 @@ func (idx *Index) ListPack(id restic.ID) (list []restic.PackedBlob) {
idx.m.Lock()
defer idx.m.Unlock()
for h, packList := range idx.pack {
for _, entry := range packList {
if entry.packID == id {
list = append(list, restic.PackedBlob{
Blob: restic.Blob{
ID: h.ID,
Type: h.Type,
Length: entry.length,
Offset: entry.offset,
},
PackID: entry.packID,
})
for h, entry := range idx.blob {
for _, blob := range idx.withDuplicates(h, entry) {
if idx.packs[blob.packIndex] == id {
list = append(list, idx.indexEntryToPackedBlob(h, blob))
}
}
}
@ -179,7 +254,7 @@ func (idx *Index) Has(id restic.ID, tpe restic.BlobType) bool {
h := restic.BlobHandle{ID: id, Type: tpe}
_, ok := idx.pack[h]
_, ok := idx.blob[h]
return ok
}
@ -227,20 +302,12 @@ func (idx *Index) Each(ctx context.Context) <-chan restic.PackedBlob {
close(ch)
}()
for h, packs := range idx.pack {
for _, blob := range packs {
for h, entry := range idx.blob {
for _, blob := range idx.withDuplicates(h, entry) {
select {
case <-ctx.Done():
return
case ch <- restic.PackedBlob{
Blob: restic.Blob{
ID: h.ID,
Type: h.Type,
Offset: blob.offset,
Length: blob.length,
},
PackID: blob.packID,
}:
case ch <- idx.indexEntryToPackedBlob(h, blob):
}
}
}
@ -255,10 +322,8 @@ func (idx *Index) Packs() restic.IDSet {
defer idx.m.Unlock()
packs := restic.NewIDSet()
for _, list := range idx.pack {
for _, entry := range list {
packs.Insert(entry.packID)
}
for _, packID := range idx.packs {
packs.Insert(packID)
}
return packs
@ -270,12 +335,17 @@ func (idx *Index) Count(t restic.BlobType) (n uint) {
idx.m.Lock()
defer idx.m.Unlock()
for h, list := range idx.pack {
for h := range idx.blob {
if h.Type != t {
continue
}
n += uint(len(list))
n++
}
for h, dups := range idx.duplicates {
if h.Type != t {
continue
}
n += uint(len(dups))
}
return
@ -298,25 +368,20 @@ func (idx *Index) generatePackList() ([]*packJSON, error) {
list := []*packJSON{}
packs := make(map[restic.ID]*packJSON)
for h, packedBlobs := range idx.pack {
for _, blob := range packedBlobs {
if blob.packID.IsNull() {
for h, entry := range idx.blob {
for _, blob := range idx.withDuplicates(h, entry) {
packID := idx.packs[blob.packIndex]
if packID.IsNull() {
panic("null pack id")
}
debug.Log("handle blob %v", h)
if blob.packID.IsNull() {
debug.Log("blob %v has no packID! (offset %v, length %v)",
h, blob.offset, blob.length)
return nil, errors.Errorf("unable to serialize index: pack for blob %v hasn't been written yet", h)
}
// see if pack is already in map
p, ok := packs[blob.packID]
p, ok := packs[packID]
if !ok {
// else create new pack
p = &packJSON{ID: blob.packID}
p = &packJSON{ID: packID}
// and append it to the list and map
list = append(list, p)
@ -327,8 +392,8 @@ func (idx *Index) generatePackList() ([]*packJSON, error) {
p.Blobs = append(p.Blobs, blobJSON{
ID: h.ID,
Type: h.Type,
Offset: blob.offset,
Length: blob.length,
Offset: uint(blob.offset),
Length: uint(blob.length),
})
}
}
@ -376,6 +441,8 @@ func (idx *Index) Finalize() {
defer idx.m.Unlock()
idx.final = true
// clear packIDToIndex as no more elements will be added
idx.packIDToIndex = nil
}
// ID returns the ID of the index, if available. If the index is not yet
@ -480,16 +547,14 @@ func DecodeIndex(buf []byte) (idx *Index, err error) {
idx = NewIndex()
for _, pack := range idxJSON.Packs {
var data, tree bool
packID := idx.addToPacks(pack.ID)
for _, blob := range pack.Blobs {
idx.store(restic.PackedBlob{
Blob: restic.Blob{
Type: blob.Type,
ID: blob.ID,
Offset: blob.Offset,
Length: blob.Length,
},
PackID: pack.ID,
idx.store(packID, restic.Blob{
Type: blob.Type,
ID: blob.ID,
Offset: blob.Offset,
Length: blob.Length,
})
switch blob.Type {
@ -525,16 +590,14 @@ func DecodeOldIndex(buf []byte) (idx *Index, err error) {
idx = NewIndex()
for _, pack := range list {
var data, tree bool
packID := idx.addToPacks(pack.ID)
for _, blob := range pack.Blobs {
idx.store(restic.PackedBlob{
Blob: restic.Blob{
Type: blob.Type,
ID: blob.ID,
Offset: blob.Offset,
Length: blob.Length,
},
PackID: pack.ID,
idx.store(packID, restic.Blob{
Type: blob.Type,
ID: blob.ID,
Offset: blob.Offset,
Length: blob.Length,
})
switch blob.Type {

22
internal/repository/index_test.go
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@ -398,18 +398,16 @@ func createRandomIndex(rng *rand.Rand) (idx *repository.Index, lookupID restic.I
// create index with 200k pack files
for i := 0; i < 200000; i++ {
packID := NewRandomTestID(rng)
var blobs []restic.Blob
offset := 0
for offset < maxPackSize {
size := 2000 + rand.Intn(4*1024*1024)
id := NewRandomTestID(rng)
idx.Store(restic.PackedBlob{
PackID: packID,
Blob: restic.Blob{
Type: restic.DataBlob,
ID: id,
Length: uint(size),
Offset: uint(offset),
},
blobs = append(blobs, restic.Blob{
Type: restic.DataBlob,
ID: id,
Length: uint(size),
Offset: uint(offset),
})
offset += size
@ -418,6 +416,7 @@ func createRandomIndex(rng *rand.Rand) (idx *repository.Index, lookupID restic.I
lookupID = id
}
}
idx.StorePack(packID, blobs)
}
return idx, lookupID
@ -444,6 +443,13 @@ func BenchmarkIndexHasKnown(b *testing.B) {
}
}
func BenchmarkIndexAlloc(b *testing.B) {
b.ReportAllocs()
for i := 0; i < b.N; i++ {
createRandomIndex(rand.New(rand.NewSource(0)))
}
}
func TestIndexHas(t *testing.T) {
type testEntry struct {
id restic.ID

13
internal/repository/master_index.go
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@ -132,19 +132,6 @@ func (mi *MasterIndex) Insert(idx *Index) {
mi.idx = append(mi.idx, idx)
}
// Remove deletes an index from the MasterIndex.
func (mi *MasterIndex) Remove(index *Index) {
mi.idxMutex.Lock()
defer mi.idxMutex.Unlock()
for i, idx := range mi.idx {
if idx == index {
mi.idx = append(mi.idx[:i], mi.idx[i+1:]...)
return
}
}
}
// Store remembers the id and pack in the index.
func (mi *MasterIndex) StorePack(id restic.ID, blobs []restic.Blob) {
mi.idxMutex.Lock()