Use commit graph files for listing pages (#7314)

* Experimental support for git commit graph files and bloom filter index

Signed-off-by: Filip Navara <filip.navara@gmail.com>

* Force vendor of commitgraph

Signed-off-by: Filip Navara <filip.navara@gmail.com>

* Remove bloom filter experiment and debug prints

* Remove old code for building commit graphs

* Remove unused function

* Remove mmap usage

* gofmt

* sort vendor/modules.txt

* Add copyright header and log commit-graph error

modules/git/commit_info.go

@@ -8,6 +8,7 @@ import (
 	"github.com/emirpasic/gods/trees/binaryheap"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	cgobject "gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph"
 )
 
 // GetCommitsInfo gets information of all commits that are corresponding to these entries
@@ -19,7 +20,12 @@ func (tes Entries) GetCommitsInfo(commit *Commit, treePath string, cache LastCom
 		entryPaths[i+1] = entry.Name()
 	}
 
-	c, err := commit.repo.gogitRepo.CommitObject(plumbing.Hash(commit.ID))
+	commitNodeIndex, commitGraphFile := commit.repo.CommitNodeIndex()
+	if commitGraphFile != nil {
+		defer commitGraphFile.Close()
+	}
+
+	c, err := commitNodeIndex.Get(plumbing.Hash(commit.ID))
 	if err != nil {
 		return nil, nil, err
 	}
@@ -69,14 +75,14 @@ func (tes Entries) GetCommitsInfo(commit *Commit, treePath string, cache LastCom
 }
 
 type commitAndPaths struct {
-	commit *object.Commit
+	commit cgobject.CommitNode
 	// Paths that are still on the branch represented by commit
 	paths []string
 	// Set of hashes for the paths
 	hashes map[string]plumbing.Hash
 }
 
-func getCommitTree(c *object.Commit, treePath string) (*object.Tree, error) {
+func getCommitTree(c cgobject.CommitNode, treePath string) (*object.Tree, error) {
 	tree, err := c.Tree()
 	if err != nil {
 		return nil, err
@@ -93,7 +99,7 @@ func getCommitTree(c *object.Commit, treePath string) (*object.Tree, error) {
 	return tree, nil
 }
 
-func getFileHashes(c *object.Commit, treePath string, paths []string) (map[string]plumbing.Hash, error) {
+func getFileHashes(c cgobject.CommitNode, treePath string, paths []string) (map[string]plumbing.Hash, error) {
 	tree, err := getCommitTree(c, treePath)
 	if err == object.ErrDirectoryNotFound {
 		// The whole tree didn't exist, so return empty map
@@ -118,16 +124,16 @@ func getFileHashes(c *object.Commit, treePath string, paths []string) (map[strin
 	return hashes, nil
 }
 
-func getLastCommitForPaths(c *object.Commit, treePath string, paths []string) (map[string]*object.Commit, error) {
+func getLastCommitForPaths(c cgobject.CommitNode, treePath string, paths []string) (map[string]*object.Commit, error) {
 	// We do a tree traversal with nodes sorted by commit time
 	heap := binaryheap.NewWith(func(a, b interface{}) int {
-		if a.(*commitAndPaths).commit.Committer.When.Before(b.(*commitAndPaths).commit.Committer.When) {
+		if a.(*commitAndPaths).commit.CommitTime().Before(b.(*commitAndPaths).commit.CommitTime()) {
 			return 1
 		}
 		return -1
 	})
 
-	result := make(map[string]*object.Commit)
+	resultNodes := make(map[string]cgobject.CommitNode)
 	initialHashes, err := getFileHashes(c, treePath, paths)
 	if err != nil {
 		return nil, err
@@ -145,9 +151,9 @@ func getLastCommitForPaths(c *object.Commit, treePath string, paths []string) (m
 
 		// Load the parent commits for the one we are currently examining
 		numParents := current.commit.NumParents()
-		var parents []*object.Commit
+		var parents []cgobject.CommitNode
 		for i := 0; i < numParents; i++ {
-			parent, err := current.commit.Parent(i)
+			parent, err := current.commit.ParentNode(i)
 			if err != nil {
 				break
 			}
@@ -174,7 +180,7 @@ func getLastCommitForPaths(c *object.Commit, treePath string, paths []string) (m
 		for i, path := range current.paths {
 			// The results could already contain some newer change for the same path,
 			// so don't override that and bail out on the file early.
-			if result[path] == nil {
+			if resultNodes[path] == nil {
 				if pathUnchanged[i] {
 					// The path existed with the same hash in at least one parent so it could
 					// not have been changed in this commit directly.
@@ -188,7 +194,7 @@ func getLastCommitForPaths(c *object.Commit, treePath string, paths []string) (m
 					// - We are looking at a merge commit and the hash of the file doesn't
 					//   match any of the hashes being merged. This is more common for directories,
 					//   but it can also happen if a file is changed through conflict resolution.
-					result[path] = current.commit
+					resultNodes[path] = current.commit
 				}
 			}
 		}
@@ -222,5 +228,15 @@ func getLastCommitForPaths(c *object.Commit, treePath string, paths []string) (m
 		}
 	}
 
+	// Post-processing
+	result := make(map[string]*object.Commit)
+	for path, commitNode := range resultNodes {
+		var err error
+		result[path], err = commitNode.Commit()
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	return result, nil
 }

modules/git/notes.go

@@ -50,7 +50,17 @@ func GetNote(repo *Repository, commitID string, note *Note) error {
 		return err
 	}
 
-	lastCommits, err := getLastCommitForPaths(commit, "", []string{commitID})
+	commitNodeIndex, commitGraphFile := repo.CommitNodeIndex()
+	if commitGraphFile != nil {
+		defer commitGraphFile.Close()
+	}
+
+	commitNode, err := commitNodeIndex.Get(commit.Hash)
+	if err != nil {
+		return nil
+	}
+
+	lastCommits, err := getLastCommitForPaths(commitNode, "", []string{commitID})
 	if err != nil {
 		return err
 	}

modules/git/repo_commitgraph.go

@@ -0,0 +1,35 @@
+// Copyright 2019 The Gitea Authors.
+// All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package git
+
+import (
+	"os"
+	"path"
+
+	gitealog "code.gitea.io/gitea/modules/log"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph"
+	cgobject "gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph"
+)
+
+// CommitNodeIndex returns the index for walking commit graph
+func (r *Repository) CommitNodeIndex() (cgobject.CommitNodeIndex, *os.File) {
+	indexPath := path.Join(r.Path, "objects", "info", "commit-graph")
+
+	file, err := os.Open(indexPath)
+	if err == nil {
+		var index commitgraph.Index
+		index, err = commitgraph.OpenFileIndex(file)
+		if err == nil {
+			return cgobject.NewGraphCommitNodeIndex(index, r.gogitRepo.Storer), file
+		}
+	}
+
+	if !os.IsNotExist(err) {
+		gitealog.Warn("Unable to read commit-graph for %s: %v", r.Path, err)
+	}
+
+	return cgobject.NewObjectCommitNodeIndex(r.gogitRepo.Storer), nil
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph/commitgraph.go

@@ -0,0 +1,35 @@
+package commitgraph
+
+import (
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+// CommitData is a reduced representation of Commit as presented in the commit graph
+// file. It is merely useful as an optimization for walking the commit graphs.
+type CommitData struct {
+	// TreeHash is the hash of the root tree of the commit.
+	TreeHash plumbing.Hash
+	// ParentIndexes are the indexes of the parent commits of the commit.
+	ParentIndexes []int
+	// ParentHashes are the hashes of the parent commits of the commit.
+	ParentHashes []plumbing.Hash
+	// Generation number is the pre-computed generation in the commit graph
+	// or zero if not available
+	Generation int
+	// When is the timestamp of the commit.
+	When time.Time
+}
+
+// Index represents a representation of commit graph that allows indexed
+// access to the nodes using commit object hash
+type Index interface {
+	// GetIndexByHash gets the index in the commit graph from commit hash, if available
+	GetIndexByHash(h plumbing.Hash) (int, error)
+	// GetNodeByIndex gets the commit node from the commit graph using index
+	// obtained from child node, if available
+	GetCommitDataByIndex(i int) (*CommitData, error)
+	// Hashes returns all the hashes that are available in the index
+	Hashes() []plumbing.Hash
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph/doc.go

@@ -0,0 +1,103 @@
+// Package commitgraph implements encoding and decoding of commit-graph files.
+//
+// Git commit graph format
+// =======================
+//
+// The Git commit graph stores a list of commit OIDs and some associated
+// metadata, including:
+//
+// - The generation number of the commit. Commits with no parents have
+//   generation number 1; commits with parents have generation number
+//   one more than the maximum generation number of its parents. We
+//   reserve zero as special, and can be used to mark a generation
+//   number invalid or as "not computed".
+//
+// - The root tree OID.
+//
+// - The commit date.
+//
+// - The parents of the commit, stored using positional references within
+//   the graph file.
+//
+// These positional references are stored as unsigned 32-bit integers
+// corresponding to the array position within the list of commit OIDs. Due
+// to some special constants we use to track parents, we can store at most
+// (1 << 30) + (1 << 29) + (1 << 28) - 1 (around 1.8 billion) commits.
+//
+// == Commit graph files have the following format:
+//
+// In order to allow extensions that add extra data to the graph, we organize
+// the body into "chunks" and provide a binary lookup table at the beginning
+// of the body. The header includes certain values, such as number of chunks
+// and hash type.
+//
+// All 4-byte numbers are in network order.
+//
+// HEADER:
+//
+//   4-byte signature:
+//       The signature is: {'C', 'G', 'P', 'H'}
+//
+//   1-byte version number:
+//       Currently, the only valid version is 1.
+//
+//   1-byte Hash Version (1 = SHA-1)
+//       We infer the hash length (H) from this value.
+//
+//   1-byte number (C) of "chunks"
+//
+//   1-byte (reserved for later use)
+//      Current clients should ignore this value.
+//
+// CHUNK LOOKUP:
+//
+//   (C + 1) * 12 bytes listing the table of contents for the chunks:
+//       First 4 bytes describe the chunk id. Value 0 is a terminating label.
+//       Other 8 bytes provide the byte-offset in current file for chunk to
+//       start. (Chunks are ordered contiguously in the file, so you can infer
+//       the length using the next chunk position if necessary.) Each chunk
+//       ID appears at most once.
+//
+//   The remaining data in the body is described one chunk at a time, and
+//   these chunks may be given in any order. Chunks are required unless
+//   otherwise specified.
+//
+// CHUNK DATA:
+//
+//   OID Fanout (ID: {'O', 'I', 'D', 'F'}) (256 * 4 bytes)
+//       The ith entry, F[i], stores the number of OIDs with first
+//       byte at most i. Thus F[255] stores the total
+//       number of commits (N).
+//
+//   OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
+//       The OIDs for all commits in the graph, sorted in ascending order.
+//
+//   Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)
+//     * The first H bytes are for the OID of the root tree.
+//     * The next 8 bytes are for the positions of the first two parents
+//       of the ith commit. Stores value 0x7000000 if no parent in that
+//       position. If there are more than two parents, the second value
+//       has its most-significant bit on and the other bits store an array
+//       position into the Extra Edge List chunk.
+//     * The next 8 bytes store the generation number of the commit and
+//       the commit time in seconds since EPOCH. The generation number
+//       uses the higher 30 bits of the first 4 bytes, while the commit
+//       time uses the 32 bits of the second 4 bytes, along with the lowest
+//       2 bits of the lowest byte, storing the 33rd and 34th bit of the
+//       commit time.
+//
+//   Extra Edge List (ID: {'E', 'D', 'G', 'E'}) [Optional]
+//       This list of 4-byte values store the second through nth parents for
+//       all octopus merges. The second parent value in the commit data stores
+//       an array position within this list along with the most-significant bit
+//       on. Starting at that array position, iterate through this list of commit
+//       positions for the parents until reaching a value with the most-significant
+//       bit on. The other bits correspond to the position of the last parent.
+//
+// TRAILER:
+//
+// 	H-byte HASH-checksum of all of the above.
+//
+// Source:
+// https://raw.githubusercontent.com/git/git/master/Documentation/technical/commit-graph-format.txt
+package commitgraph

vendor/gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph/encoder.go

@@ -0,0 +1,190 @@
+package commitgraph
+
+import (
+	"crypto/sha1"
+	"hash"
+	"io"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/utils/binary"
+)
+
+// Encoder writes MemoryIndex structs to an output stream.
+type Encoder struct {
+	io.Writer
+	hash hash.Hash
+}
+
+// NewEncoder returns a new stream encoder that writes to w.
+func NewEncoder(w io.Writer) *Encoder {
+	h := sha1.New()
+	mw := io.MultiWriter(w, h)
+	return &Encoder{mw, h}
+}
+
+// Encode writes an index into the commit-graph file
+func (e *Encoder) Encode(idx Index) error {
+	var err error
+
+	// Get all the hashes in the input index
+	hashes := idx.Hashes()
+
+	// Sort the inout and prepare helper structures we'll need for encoding
+	hashToIndex, fanout, extraEdgesCount := e.prepare(idx, hashes)
+
+	chunkSignatures := [][]byte{oidFanoutSignature, oidLookupSignature, commitDataSignature}
+	chunkSizes := []uint64{4 * 256, uint64(len(hashes)) * 20, uint64(len(hashes)) * 36}
+	if extraEdgesCount > 0 {
+		chunkSignatures = append(chunkSignatures, extraEdgeListSignature)
+		chunkSizes = append(chunkSizes, uint64(extraEdgesCount)*4)
+	}
+
+	if err = e.encodeFileHeader(len(chunkSignatures)); err != nil {
+		return err
+	}
+	if err = e.encodeChunkHeaders(chunkSignatures, chunkSizes); err != nil {
+		return err
+	}
+	if err = e.encodeFanout(fanout); err != nil {
+		return err
+	}
+	if err = e.encodeOidLookup(hashes); err != nil {
+		return err
+	}
+	if extraEdges, err := e.encodeCommitData(hashes, hashToIndex, idx); err == nil {
+		if err = e.encodeExtraEdges(extraEdges); err != nil {
+			return err
+		}
+	}
+	if err != nil {
+		return err
+	}
+	return e.encodeChecksum()
+}
+
+func (e *Encoder) prepare(idx Index, hashes []plumbing.Hash) (hashToIndex map[plumbing.Hash]uint32, fanout []uint32, extraEdgesCount uint32) {
+	// Sort the hashes and build our index
+	plumbing.HashesSort(hashes)
+	hashToIndex = make(map[plumbing.Hash]uint32)
+	fanout = make([]uint32, 256)
+	for i, hash := range hashes {
+		hashToIndex[hash] = uint32(i)
+		fanout[hash[0]]++
+	}
+
+	// Convert the fanout to cumulative values
+	for i := 1; i <= 0xff; i++ {
+		fanout[i] += fanout[i-1]
+	}
+
+	// Find out if we will need extra edge table
+	for i := 0; i < len(hashes); i++ {
+		v, _ := idx.GetCommitDataByIndex(i)
+		if len(v.ParentHashes) > 2 {
+			extraEdgesCount += uint32(len(v.ParentHashes) - 1)
+			break
+		}
+	}
+
+	return
+}
+
+func (e *Encoder) encodeFileHeader(chunkCount int) (err error) {
+	if _, err = e.Write(commitFileSignature); err == nil {
+		_, err = e.Write([]byte{1, 1, byte(chunkCount), 0})
+	}
+	return
+}
+
+func (e *Encoder) encodeChunkHeaders(chunkSignatures [][]byte, chunkSizes []uint64) (err error) {
+	// 8 bytes of file header, 12 bytes for each chunk header and 12 byte for terminator
+	offset := uint64(8 + len(chunkSignatures)*12 + 12)
+	for i, signature := range chunkSignatures {
+		if _, err = e.Write(signature); err == nil {
+			err = binary.WriteUint64(e, offset)
+		}
+		if err != nil {
+			return
+		}
+		offset += chunkSizes[i]
+	}
+	if _, err = e.Write(lastSignature); err == nil {
+		err = binary.WriteUint64(e, offset)
+	}
+	return
+}
+
+func (e *Encoder) encodeFanout(fanout []uint32) (err error) {
+	for i := 0; i <= 0xff; i++ {
+		if err = binary.WriteUint32(e, fanout[i]); err != nil {
+			return
+		}
+	}
+	return
+}
+
+func (e *Encoder) encodeOidLookup(hashes []plumbing.Hash) (err error) {
+	for _, hash := range hashes {
+		if _, err = e.Write(hash[:]); err != nil {
+			return err
+		}
+	}
+	return
+}
+
+func (e *Encoder) encodeCommitData(hashes []plumbing.Hash, hashToIndex map[plumbing.Hash]uint32, idx Index) (extraEdges []uint32, err error) {
+	for _, hash := range hashes {
+		origIndex, _ := idx.GetIndexByHash(hash)
+		commitData, _ := idx.GetCommitDataByIndex(origIndex)
+		if _, err = e.Write(commitData.TreeHash[:]); err != nil {
+			return
+		}
+
+		var parent1, parent2 uint32
+		if len(commitData.ParentHashes) == 0 {
+			parent1 = parentNone
+			parent2 = parentNone
+		} else if len(commitData.ParentHashes) == 1 {
+			parent1 = hashToIndex[commitData.ParentHashes[0]]
+			parent2 = parentNone
+		} else if len(commitData.ParentHashes) == 2 {
+			parent1 = hashToIndex[commitData.ParentHashes[0]]
+			parent2 = hashToIndex[commitData.ParentHashes[1]]
+		} else if len(commitData.ParentHashes) > 2 {
+			parent1 = hashToIndex[commitData.ParentHashes[0]]
+			parent2 = uint32(len(extraEdges)) | parentOctopusUsed
+			for _, parentHash := range commitData.ParentHashes[1:] {
+				extraEdges = append(extraEdges, hashToIndex[parentHash])
+			}
+			extraEdges[len(extraEdges)-1] |= parentLast
+		}
+
+		if err = binary.WriteUint32(e, parent1); err == nil {
+			err = binary.WriteUint32(e, parent2)
+		}
+		if err != nil {
+			return
+		}
+
+		unixTime := uint64(commitData.When.Unix())
+		unixTime |= uint64(commitData.Generation) << 34
+		if err = binary.WriteUint64(e, unixTime); err != nil {
+			return
+		}
+	}
+	return
+}
+
+func (e *Encoder) encodeExtraEdges(extraEdges []uint32) (err error) {
+	for _, parent := range extraEdges {
+		if err = binary.WriteUint32(e, parent); err != nil {
+			return
+		}
+	}
+	return
+}
+
+func (e *Encoder) encodeChecksum() error {
+	_, err := e.Write(e.hash.Sum(nil)[:20])
+	return err
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph/file.go

@@ -0,0 +1,259 @@
+package commitgraph
+
+import (
+	"bytes"
+	encbin "encoding/binary"
+	"errors"
+	"io"
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/utils/binary"
+)
+
+var (
+	// ErrUnsupportedVersion is returned by OpenFileIndex when the commit graph
+	// file version is not supported.
+	ErrUnsupportedVersion = errors.New("Unsupported version")
+	// ErrUnsupportedHash is returned by OpenFileIndex when the commit graph
+	// hash function is not supported. Currently only SHA-1 is defined and
+	// supported
+	ErrUnsupportedHash = errors.New("Unsupported hash algorithm")
+	// ErrMalformedCommitGraphFile is returned by OpenFileIndex when the commit
+	// graph file is corrupted.
+	ErrMalformedCommitGraphFile = errors.New("Malformed commit graph file")
+
+	commitFileSignature    = []byte{'C', 'G', 'P', 'H'}
+	oidFanoutSignature     = []byte{'O', 'I', 'D', 'F'}
+	oidLookupSignature     = []byte{'O', 'I', 'D', 'L'}
+	commitDataSignature    = []byte{'C', 'D', 'A', 'T'}
+	extraEdgeListSignature = []byte{'E', 'D', 'G', 'E'}
+	lastSignature          = []byte{0, 0, 0, 0}
+
+	parentNone        = uint32(0x70000000)
+	parentOctopusUsed = uint32(0x80000000)
+	parentOctopusMask = uint32(0x7fffffff)
+	parentLast        = uint32(0x80000000)
+)
+
+type fileIndex struct {
+	reader              io.ReaderAt
+	fanout              [256]int
+	oidFanoutOffset     int64
+	oidLookupOffset     int64
+	commitDataOffset    int64
+	extraEdgeListOffset int64
+}
+
+// OpenFileIndex opens a serialized commit graph file in the format described at
+// https://github.com/git/git/blob/master/Documentation/technical/commit-graph-format.txt
+func OpenFileIndex(reader io.ReaderAt) (Index, error) {
+	fi := &fileIndex{reader: reader}
+
+	if err := fi.verifyFileHeader(); err != nil {
+		return nil, err
+	}
+	if err := fi.readChunkHeaders(); err != nil {
+		return nil, err
+	}
+	if err := fi.readFanout(); err != nil {
+		return nil, err
+	}
+
+	return fi, nil
+}
+
+func (fi *fileIndex) verifyFileHeader() error {
+	// Verify file signature
+	var signature = make([]byte, 4)
+	if _, err := fi.reader.ReadAt(signature, 0); err != nil {
+		return err
+	}
+	if !bytes.Equal(signature, commitFileSignature) {
+		return ErrMalformedCommitGraphFile
+	}
+
+	// Read and verify the file header
+	var header = make([]byte, 4)
+	if _, err := fi.reader.ReadAt(header, 4); err != nil {
+		return err
+	}
+	if header[0] != 1 {
+		return ErrUnsupportedVersion
+	}
+	if header[1] != 1 {
+		return ErrUnsupportedHash
+	}
+
+	return nil
+}
+
+func (fi *fileIndex) readChunkHeaders() error {
+	var chunkID = make([]byte, 4)
+	for i := 0; ; i++ {
+		chunkHeader := io.NewSectionReader(fi.reader, 8+(int64(i)*12), 12)
+		if _, err := io.ReadAtLeast(chunkHeader, chunkID, 4); err != nil {
+			return err
+		}
+		chunkOffset, err := binary.ReadUint64(chunkHeader)
+		if err != nil {
+			return err
+		}
+
+		if bytes.Equal(chunkID, oidFanoutSignature) {
+			fi.oidFanoutOffset = int64(chunkOffset)
+		} else if bytes.Equal(chunkID, oidLookupSignature) {
+			fi.oidLookupOffset = int64(chunkOffset)
+		} else if bytes.Equal(chunkID, commitDataSignature) {
+			fi.commitDataOffset = int64(chunkOffset)
+		} else if bytes.Equal(chunkID, extraEdgeListSignature) {
+			fi.extraEdgeListOffset = int64(chunkOffset)
+		} else if bytes.Equal(chunkID, lastSignature) {
+			break
+		}
+	}
+
+	if fi.oidFanoutOffset <= 0 || fi.oidLookupOffset <= 0 || fi.commitDataOffset <= 0 {
+		return ErrMalformedCommitGraphFile
+	}
+
+	return nil
+}
+
+func (fi *fileIndex) readFanout() error {
+	fanoutReader := io.NewSectionReader(fi.reader, fi.oidFanoutOffset, 256*4)
+	for i := 0; i < 256; i++ {
+		fanoutValue, err := binary.ReadUint32(fanoutReader)
+		if err != nil {
+			return err
+		}
+		if fanoutValue > 0x7fffffff {
+			return ErrMalformedCommitGraphFile
+		}
+		fi.fanout[i] = int(fanoutValue)
+	}
+	return nil
+}
+
+func (fi *fileIndex) GetIndexByHash(h plumbing.Hash) (int, error) {
+	var oid plumbing.Hash
+
+	// Find the hash in the oid lookup table
+	var low int
+	if h[0] == 0 {
+		low = 0
+	} else {
+		low = fi.fanout[h[0]-1]
+	}
+	high := fi.fanout[h[0]]
+	for low < high {
+		mid := (low + high) >> 1
+		offset := fi.oidLookupOffset + int64(mid)*20
+		if _, err := fi.reader.ReadAt(oid[:], offset); err != nil {
+			return 0, err
+		}
+		cmp := bytes.Compare(h[:], oid[:])
+		if cmp < 0 {
+			high = mid
+		} else if cmp == 0 {
+			return mid, nil
+		} else {
+			low = mid + 1
+		}
+	}
+
+	return 0, plumbing.ErrObjectNotFound
+}
+
+func (fi *fileIndex) GetCommitDataByIndex(idx int) (*CommitData, error) {
+	if idx >= fi.fanout[0xff] {
+		return nil, plumbing.ErrObjectNotFound
+	}
+
+	offset := fi.commitDataOffset + int64(idx)*36
+	commitDataReader := io.NewSectionReader(fi.reader, offset, 36)
+
+	treeHash, err := binary.ReadHash(commitDataReader)
+	if err != nil {
+		return nil, err
+	}
+	parent1, err := binary.ReadUint32(commitDataReader)
+	if err != nil {
+		return nil, err
+	}
+	parent2, err := binary.ReadUint32(commitDataReader)
+	if err != nil {
+		return nil, err
+	}
+	genAndTime, err := binary.ReadUint64(commitDataReader)
+	if err != nil {
+		return nil, err
+	}
+
+	var parentIndexes []int
+	if parent2&parentOctopusUsed == parentOctopusUsed {
+		// Octopus merge
+		parentIndexes = []int{int(parent1 & parentOctopusMask)}
+		offset := fi.extraEdgeListOffset + 4*int64(parent2&parentOctopusMask)
+		buf := make([]byte, 4)
+		for {
+			_, err := fi.reader.ReadAt(buf, offset)
+			if err != nil {
+				return nil, err
+			}
+
+			parent := encbin.BigEndian.Uint32(buf)
+			offset += 4
+			parentIndexes = append(parentIndexes, int(parent&parentOctopusMask))
+			if parent&parentLast == parentLast {
+				break
+			}
+		}
+	} else if parent2 != parentNone {
+		parentIndexes = []int{int(parent1 & parentOctopusMask), int(parent2 & parentOctopusMask)}
+	} else if parent1 != parentNone {
+		parentIndexes = []int{int(parent1 & parentOctopusMask)}
+	}
+
+	parentHashes, err := fi.getHashesFromIndexes(parentIndexes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &CommitData{
+		TreeHash:      treeHash,
+		ParentIndexes: parentIndexes,
+		ParentHashes:  parentHashes,
+		Generation:    int(genAndTime >> 34),
+		When:          time.Unix(int64(genAndTime&0x3FFFFFFFF), 0),
+	}, nil
+}
+
+func (fi *fileIndex) getHashesFromIndexes(indexes []int) ([]plumbing.Hash, error) {
+	hashes := make([]plumbing.Hash, len(indexes))
+
+	for i, idx := range indexes {
+		if idx >= fi.fanout[0xff] {
+			return nil, ErrMalformedCommitGraphFile
+		}
+
+		offset := fi.oidLookupOffset + int64(idx)*20
+		if _, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil {
+			return nil, err
+		}
+	}
+
+	return hashes, nil
+}
+
+// Hashes returns all the hashes that are available in the index
+func (fi *fileIndex) Hashes() []plumbing.Hash {
+	hashes := make([]plumbing.Hash, fi.fanout[0xff])
+	for i := 0; i < int(fi.fanout[0xff]); i++ {
+		offset := fi.oidLookupOffset + int64(i)*20
+		if n, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil || n < 20 {
+			return nil
+		}
+	}
+	return hashes
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph/memory.go

@@ -0,0 +1,72 @@
+package commitgraph
+
+import (
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+// MemoryIndex provides a way to build the commit-graph in memory
+// for later encoding to file.
+type MemoryIndex struct {
+	commitData []*CommitData
+	indexMap   map[plumbing.Hash]int
+}
+
+// NewMemoryIndex creates in-memory commit graph representation
+func NewMemoryIndex() *MemoryIndex {
+	return &MemoryIndex{
+		indexMap: make(map[plumbing.Hash]int),
+	}
+}
+
+// GetIndexByHash gets the index in the commit graph from commit hash, if available
+func (mi *MemoryIndex) GetIndexByHash(h plumbing.Hash) (int, error) {
+	i, ok := mi.indexMap[h]
+	if ok {
+		return i, nil
+	}
+
+	return 0, plumbing.ErrObjectNotFound
+}
+
+// GetCommitDataByIndex gets the commit node from the commit graph using index
+// obtained from child node, if available
+func (mi *MemoryIndex) GetCommitDataByIndex(i int) (*CommitData, error) {
+	if int(i) >= len(mi.commitData) {
+		return nil, plumbing.ErrObjectNotFound
+	}
+
+	commitData := mi.commitData[i]
+
+	// Map parent hashes to parent indexes
+	if commitData.ParentIndexes == nil {
+		parentIndexes := make([]int, len(commitData.ParentHashes))
+		for i, parentHash := range commitData.ParentHashes {
+			var err error
+			if parentIndexes[i], err = mi.GetIndexByHash(parentHash); err != nil {
+				return nil, err
+			}
+		}
+		commitData.ParentIndexes = parentIndexes
+	}
+
+	return commitData, nil
+}
+
+// Hashes returns all the hashes that are available in the index
+func (mi *MemoryIndex) Hashes() []plumbing.Hash {
+	hashes := make([]plumbing.Hash, 0, len(mi.indexMap))
+	for k := range mi.indexMap {
+		hashes = append(hashes, k)
+	}
+	return hashes
+}
+
+// Add adds new node to the memory index
+func (mi *MemoryIndex) Add(hash plumbing.Hash, commitData *CommitData) {
+	// The parent indexes are calculated lazily in GetNodeByIndex
+	// which allows adding nodes out of order as long as all parents
+	// are eventually resolved
+	commitData.ParentIndexes = nil
+	mi.indexMap[hash] = len(mi.commitData)
+	mi.commitData = append(mi.commitData, commitData)
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph/commitnode.go

@@ -0,0 +1,98 @@
+package commitgraph
+
+import (
+	"io"
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+// CommitNode is generic interface encapsulating a lightweight commit object retrieved
+// from CommitNodeIndex
+type CommitNode interface {
+	// ID returns the Commit object id referenced by the commit graph node.
+	ID() plumbing.Hash
+	// Tree returns the Tree referenced by the commit graph node.
+	Tree() (*object.Tree, error)
+	// CommitTime returns the Commiter.When time of the Commit referenced by the commit graph node.
+	CommitTime() time.Time
+	// NumParents returns the number of parents in a commit.
+	NumParents() int
+	// ParentNodes return a CommitNodeIter for parents of specified node.
+	ParentNodes() CommitNodeIter
+	// ParentNode returns the ith parent of a commit.
+	ParentNode(i int) (CommitNode, error)
+	// ParentHashes returns hashes of the parent commits for a specified node
+	ParentHashes() []plumbing.Hash
+	// Generation returns the generation of the commit for reachability analysis.
+	// Objects with newer generation are not reachable from objects of older generation.
+	Generation() uint64
+	// Commit returns the full commit object from the node
+	Commit() (*object.Commit, error)
+}
+
+// CommitNodeIndex is generic interface encapsulating an index of CommitNode objects
+type CommitNodeIndex interface {
+	// Get returns a commit node from a commit hash
+	Get(hash plumbing.Hash) (CommitNode, error)
+}
+
+// CommitNodeIter is a generic closable interface for iterating over commit nodes.
+type CommitNodeIter interface {
+	Next() (CommitNode, error)
+	ForEach(func(CommitNode) error) error
+	Close()
+}
+
+// parentCommitNodeIter provides an iterator for parent commits from associated CommitNodeIndex.
+type parentCommitNodeIter struct {
+	node CommitNode
+	i    int
+}
+
+func newParentgraphCommitNodeIter(node CommitNode) CommitNodeIter {
+	return &parentCommitNodeIter{node, 0}
+}
+
+// Next moves the iterator to the next commit and returns a pointer to it. If
+// there are no more commits, it returns io.EOF.
+func (iter *parentCommitNodeIter) Next() (CommitNode, error) {
+	obj, err := iter.node.ParentNode(iter.i)
+	if err == object.ErrParentNotFound {
+		return nil, io.EOF
+	}
+	if err == nil {
+		iter.i++
+	}
+
+	return obj, err
+}
+
+// ForEach call the cb function for each commit contained on this iter until
+// an error appends or the end of the iter is reached. If ErrStop is sent
+// the iteration is stopped but no error is returned. The iterator is closed.
+func (iter *parentCommitNodeIter) ForEach(cb func(CommitNode) error) error {
+	for {
+		obj, err := iter.Next()
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+
+			return err
+		}
+
+		if err := cb(obj); err != nil {
+			if err == storer.ErrStop {
+				return nil
+			}
+
+			return err
+		}
+	}
+}
+
+func (iter *parentCommitNodeIter) Close() {
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph/commitnode_graph.go

@@ -0,0 +1,131 @@
+package commitgraph
+
+import (
+	"fmt"
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+// graphCommitNode is a reduced representation of Commit as presented in the commit
+// graph file (commitgraph.Node). It is merely useful as an optimization for walking
+// the commit graphs.
+//
+// graphCommitNode implements the CommitNode interface.
+type graphCommitNode struct {
+	// Hash for the Commit object
+	hash plumbing.Hash
+	// Index of the node in the commit graph file
+	index int
+
+	commitData *commitgraph.CommitData
+	gci        *graphCommitNodeIndex
+}
+
+// graphCommitNodeIndex is an index that can load CommitNode objects from both the commit
+// graph files and the object store.
+//
+// graphCommitNodeIndex implements the CommitNodeIndex interface
+type graphCommitNodeIndex struct {
+	commitGraph commitgraph.Index
+	s           storer.EncodedObjectStorer
+}
+
+// NewGraphCommitNodeIndex returns CommitNodeIndex implementation that uses commit-graph
+// files as backing storage and falls back to object storage when necessary
+func NewGraphCommitNodeIndex(commitGraph commitgraph.Index, s storer.EncodedObjectStorer) CommitNodeIndex {
+	return &graphCommitNodeIndex{commitGraph, s}
+}
+
+func (gci *graphCommitNodeIndex) Get(hash plumbing.Hash) (CommitNode, error) {
+	// Check the commit graph first
+	parentIndex, err := gci.commitGraph.GetIndexByHash(hash)
+	if err == nil {
+		parent, err := gci.commitGraph.GetCommitDataByIndex(parentIndex)
+		if err != nil {
+			return nil, err
+		}
+
+		return &graphCommitNode{
+			hash:       hash,
+			index:      parentIndex,
+			commitData: parent,
+			gci:        gci,
+		}, nil
+	}
+
+	// Fallback to loading full commit object
+	commit, err := object.GetCommit(gci.s, hash)
+	if err != nil {
+		return nil, err
+	}
+
+	return &objectCommitNode{
+		nodeIndex: gci,
+		commit:    commit,
+	}, nil
+}
+
+func (c *graphCommitNode) ID() plumbing.Hash {
+	return c.hash
+}
+
+func (c *graphCommitNode) Tree() (*object.Tree, error) {
+	return object.GetTree(c.gci.s, c.commitData.TreeHash)
+}
+
+func (c *graphCommitNode) CommitTime() time.Time {
+	return c.commitData.When
+}
+
+func (c *graphCommitNode) NumParents() int {
+	return len(c.commitData.ParentIndexes)
+}
+
+func (c *graphCommitNode) ParentNodes() CommitNodeIter {
+	return newParentgraphCommitNodeIter(c)
+}
+
+func (c *graphCommitNode) ParentNode(i int) (CommitNode, error) {
+	if i < 0 || i >= len(c.commitData.ParentIndexes) {
+		return nil, object.ErrParentNotFound
+	}
+
+	parent, err := c.gci.commitGraph.GetCommitDataByIndex(c.commitData.ParentIndexes[i])
+	if err != nil {
+		return nil, err
+	}
+
+	return &graphCommitNode{
+		hash:       c.commitData.ParentHashes[i],
+		index:      c.commitData.ParentIndexes[i],
+		commitData: parent,
+		gci:        c.gci,
+	}, nil
+}
+
+func (c *graphCommitNode) ParentHashes() []plumbing.Hash {
+	return c.commitData.ParentHashes
+}
+
+func (c *graphCommitNode) Generation() uint64 {
+	// If the commit-graph file was generated with older Git version that
+	// set the generation to zero for every commit the generation assumption
+	// is still valid. It is just less useful.
+	return uint64(c.commitData.Generation)
+}
+
+func (c *graphCommitNode) Commit() (*object.Commit, error) {
+	return object.GetCommit(c.gci.s, c.hash)
+}
+
+func (c *graphCommitNode) String() string {
+	return fmt.Sprintf(
+		"%s %s\nDate:   %s",
+		plumbing.CommitObject, c.ID(),
+		c.CommitTime().Format(object.DateFormat),
+	)
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph/commitnode_object.go

@@ -0,0 +1,90 @@
+package commitgraph
+
+import (
+	"math"
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+// objectCommitNode is a representation of Commit as presented in the GIT object format.
+//
+// objectCommitNode implements the CommitNode interface.
+type objectCommitNode struct {
+	nodeIndex CommitNodeIndex
+	commit    *object.Commit
+}
+
+// NewObjectCommitNodeIndex returns CommitNodeIndex implementation that uses
+// only object storage to load the nodes
+func NewObjectCommitNodeIndex(s storer.EncodedObjectStorer) CommitNodeIndex {
+	return &objectCommitNodeIndex{s}
+}
+
+func (oci *objectCommitNodeIndex) Get(hash plumbing.Hash) (CommitNode, error) {
+	commit, err := object.GetCommit(oci.s, hash)
+	if err != nil {
+		return nil, err
+	}
+
+	return &objectCommitNode{
+		nodeIndex: oci,
+		commit:    commit,
+	}, nil
+}
+
+// objectCommitNodeIndex is an index that can load CommitNode objects only from the
+// object store.
+//
+// objectCommitNodeIndex implements the CommitNodeIndex interface
+type objectCommitNodeIndex struct {
+	s storer.EncodedObjectStorer
+}
+
+func (c *objectCommitNode) CommitTime() time.Time {
+	return c.commit.Committer.When
+}
+
+func (c *objectCommitNode) ID() plumbing.Hash {
+	return c.commit.ID()
+}
+
+func (c *objectCommitNode) Tree() (*object.Tree, error) {
+	return c.commit.Tree()
+}
+
+func (c *objectCommitNode) NumParents() int {
+	return c.commit.NumParents()
+}
+
+func (c *objectCommitNode) ParentNodes() CommitNodeIter {
+	return newParentgraphCommitNodeIter(c)
+}
+
+func (c *objectCommitNode) ParentNode(i int) (CommitNode, error) {
+	if i < 0 || i >= len(c.commit.ParentHashes) {
+		return nil, object.ErrParentNotFound
+	}
+
+	// Note: It's necessary to go through CommitNodeIndex here to ensure
+	// that if the commit-graph file covers only part of the history we
+	// start using it when that part is reached.
+	return c.nodeIndex.Get(c.commit.ParentHashes[i])
+}
+
+func (c *objectCommitNode) ParentHashes() []plumbing.Hash {
+	return c.commit.ParentHashes
+}
+
+func (c *objectCommitNode) Generation() uint64 {
+	// Commit nodes representing objects outside of the commit graph can never
+	// be reached by objects from the commit-graph thus we return the highest
+	// possible value.
+	return math.MaxUint64
+}
+
+func (c *objectCommitNode) Commit() (*object.Commit, error) {
+	return c.commit, nil
+}

vendor/gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph/commitnode_walker_ctime.go

@@ -0,0 +1,105 @@
+package commitgraph
+
+import (
+	"io"
+
+	"github.com/emirpasic/gods/trees/binaryheap"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+type commitNodeIteratorByCTime struct {
+	heap         *binaryheap.Heap
+	seenExternal map[plumbing.Hash]bool
+	seen         map[plumbing.Hash]bool
+}
+
+// NewCommitNodeIterCTime returns a CommitNodeIter that walks the commit history,
+// starting at the given commit and visiting its parents while preserving Committer Time order.
+// this appears to be the closest order to `git log`
+// The given callback will be called for each visited commit. Each commit will
+// be visited only once. If the callback returns an error, walking will stop
+// and will return the error. Other errors might be returned if the history
+// cannot be traversed (e.g. missing objects). Ignore allows to skip some
+// commits from being iterated.
+func NewCommitNodeIterCTime(
+	c CommitNode,
+	seenExternal map[plumbing.Hash]bool,
+	ignore []plumbing.Hash,
+) CommitNodeIter {
+	seen := make(map[plumbing.Hash]bool)
+	for _, h := range ignore {
+		seen[h] = true
+	}
+
+	heap := binaryheap.NewWith(func(a, b interface{}) int {
+		if a.(CommitNode).CommitTime().Before(b.(CommitNode).CommitTime()) {
+			return 1
+		}
+		return -1
+	})
+
+	heap.Push(c)
+
+	return &commitNodeIteratorByCTime{
+		heap:         heap,
+		seenExternal: seenExternal,
+		seen:         seen,
+	}
+}
+
+func (w *commitNodeIteratorByCTime) Next() (CommitNode, error) {
+	var c CommitNode
+	for {
+		cIn, ok := w.heap.Pop()
+		if !ok {
+			return nil, io.EOF
+		}
+		c = cIn.(CommitNode)
+		cID := c.ID()
+
+		if w.seen[cID] || w.seenExternal[cID] {
+			continue
+		}
+
+		w.seen[cID] = true
+
+		for i, h := range c.ParentHashes() {
+			if w.seen[h] || w.seenExternal[h] {
+				continue
+			}
+			pc, err := c.ParentNode(i)
+			if err != nil {
+				return nil, err
+			}
+			w.heap.Push(pc)
+		}
+
+		return c, nil
+	}
+}
+
+func (w *commitNodeIteratorByCTime) ForEach(cb func(CommitNode) error) error {
+	for {
+		c, err := w.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+
+		err = cb(c)
+		if err == storer.ErrStop {
+			break
+		}
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (w *commitNodeIteratorByCTime) Close() {}

vendor/gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph/doc.go

@@ -0,0 +1,7 @@
+// Package commitgraph provides an interface for efficient traversal over Git
+// commit graph either through the regular object storage, or optionally with
+// the index stored in commit-graph file (Git 2.18+).
+//
+// The API and functionality of this package are considered EXPERIMENTAL and is
+// not considered stable nor production ready.
+package commitgraph

vendor/modules.txt

@@ -432,7 +432,9 @@ gopkg.in/src-d/go-git.v4/config
 gopkg.in/src-d/go-git.v4/plumbing
 gopkg.in/src-d/go-git.v4/plumbing/cache
 gopkg.in/src-d/go-git.v4/plumbing/filemode
+gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph
 gopkg.in/src-d/go-git.v4/plumbing/object
+gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph
 gopkg.in/src-d/go-git.v4/storage/filesystem
 gopkg.in/src-d/go-git.v4/internal/revision
 gopkg.in/src-d/go-git.v4/plumbing/format/gitignore
@@ -455,8 +457,8 @@ gopkg.in/src-d/go-git.v4/utils/merkletrie/index
 gopkg.in/src-d/go-git.v4/utils/merkletrie/noder
 gopkg.in/src-d/go-git.v4/internal/url
 gopkg.in/src-d/go-git.v4/plumbing/format/config
-gopkg.in/src-d/go-git.v4/plumbing/format/diff
 gopkg.in/src-d/go-git.v4/utils/binary
+gopkg.in/src-d/go-git.v4/plumbing/format/diff
 gopkg.in/src-d/go-git.v4/plumbing/format/idxfile
 gopkg.in/src-d/go-git.v4/plumbing/format/objfile
 gopkg.in/src-d/go-git.v4/storage/filesystem/dotgit