diff --git a/plumbing/format/commitgraph/commitgraph.go b/plumbing/format/commitgraph/commitgraph.go
new file mode 100644
index 000000000..9bf714904
--- /dev/null
+++ b/plumbing/format/commitgraph/commitgraph.go
@@ -0,0 +1,35 @@
+package commitgraph
+
+import (
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+// Node 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 Node 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
+	GetNodeByIndex(i int) (*Node, error)
+	// Hashes returns all the hashes that are available in the index
+	Hashes() []plumbing.Hash
+}
diff --git a/plumbing/format/commitgraph/commitgraph_test.go b/plumbing/format/commitgraph/commitgraph_test.go
new file mode 100644
index 000000000..b98414251
--- /dev/null
+++ b/plumbing/format/commitgraph/commitgraph_test.go
@@ -0,0 +1,135 @@
+package commitgraph_test
+
+import (
+	"io/ioutil"
+	"os"
+	"path"
+	"testing"
+
+	"golang.org/x/exp/mmap"
+
+	. "gopkg.in/check.v1"
+	"gopkg.in/src-d/go-git-fixtures.v3"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type CommitgraphSuite struct {
+	fixtures.Suite
+}
+
+var _ = Suite(&CommitgraphSuite{})
+
+func testDecodeHelper(c *C, path string) {
+	reader, err := mmap.Open(path)
+	c.Assert(err, IsNil)
+	defer reader.Close()
+	index, err := commitgraph.OpenFileIndex(reader)
+	c.Assert(err, IsNil)
+
+	// Root commit
+	nodeIndex, err := index.GetIndexByHash(plumbing.NewHash("347c91919944a68e9413581a1bc15519550a3afe"))
+	c.Assert(err, IsNil)
+	node, err := index.GetNodeByIndex(nodeIndex)
+	c.Assert(err, IsNil)
+	c.Assert(len(node.ParentIndexes), Equals, 0)
+	c.Assert(len(node.ParentHashes), Equals, 0)
+
+	// Regular commit
+	nodeIndex, err = index.GetIndexByHash(plumbing.NewHash("e713b52d7e13807e87a002e812041f248db3f643"))
+	c.Assert(err, IsNil)
+	node, err = index.GetNodeByIndex(nodeIndex)
+	c.Assert(err, IsNil)
+	c.Assert(len(node.ParentIndexes), Equals, 1)
+	c.Assert(len(node.ParentHashes), Equals, 1)
+	c.Assert(node.ParentHashes[0].String(), Equals, "347c91919944a68e9413581a1bc15519550a3afe")
+
+	// Merge commit
+	nodeIndex, err = index.GetIndexByHash(plumbing.NewHash("b29328491a0682c259bcce28741eac71f3499f7d"))
+	c.Assert(err, IsNil)
+	node, err = index.GetNodeByIndex(nodeIndex)
+	c.Assert(err, IsNil)
+	c.Assert(len(node.ParentIndexes), Equals, 2)
+	c.Assert(len(node.ParentHashes), Equals, 2)
+	c.Assert(node.ParentHashes[0].String(), Equals, "e713b52d7e13807e87a002e812041f248db3f643")
+	c.Assert(node.ParentHashes[1].String(), Equals, "03d2c021ff68954cf3ef0a36825e194a4b98f981")
+
+	// Octopus merge commit
+	nodeIndex, err = index.GetIndexByHash(plumbing.NewHash("6f6c5d2be7852c782be1dd13e36496dd7ad39560"))
+	c.Assert(err, IsNil)
+	node, err = index.GetNodeByIndex(nodeIndex)
+	c.Assert(err, IsNil)
+	c.Assert(len(node.ParentIndexes), Equals, 3)
+	c.Assert(len(node.ParentHashes), Equals, 3)
+	c.Assert(node.ParentHashes[0].String(), Equals, "ce275064ad67d51e99f026084e20827901a8361c")
+	c.Assert(node.ParentHashes[1].String(), Equals, "bb13916df33ed23004c3ce9ed3b8487528e655c1")
+	c.Assert(node.ParentHashes[2].String(), Equals, "a45273fe2d63300e1962a9e26a6b15c276cd7082")
+
+	// Check all hashes
+	hashes := index.Hashes()
+	c.Assert(len(hashes), Equals, 11)
+	c.Assert(hashes[0].String(), Equals, "03d2c021ff68954cf3ef0a36825e194a4b98f981")
+	c.Assert(hashes[10].String(), Equals, "e713b52d7e13807e87a002e812041f248db3f643")
+}
+
+func (s *CommitgraphSuite) TestDecode(c *C) {
+	fixtures.ByTag("commit-graph").Test(c, func(f *fixtures.Fixture) {
+		dotgit := f.DotGit()
+		testDecodeHelper(c, path.Join(dotgit.Root(), "objects", "info", "commit-graph"))
+	})
+}
+
+func (s *CommitgraphSuite) TestReencode(c *C) {
+	fixtures.ByTag("commit-graph").Test(c, func(f *fixtures.Fixture) {
+		dotgit := f.DotGit()
+
+		reader, err := mmap.Open(path.Join(dotgit.Root(), "objects", "info", "commit-graph"))
+		c.Assert(err, IsNil)
+		defer reader.Close()
+		index, err := commitgraph.OpenFileIndex(reader)
+		c.Assert(err, IsNil)
+
+		writer, err := ioutil.TempFile(dotgit.Root(), "commit-graph")
+		c.Assert(err, IsNil)
+		tmpName := writer.Name()
+		defer os.Remove(tmpName)
+		encoder := commitgraph.NewEncoder(writer)
+		err = encoder.Encode(index)
+		c.Assert(err, IsNil)
+		writer.Close()
+
+		testDecodeHelper(c, tmpName)
+	})
+}
+
+func (s *CommitgraphSuite) TestReencodeInMemory(c *C) {
+	fixtures.ByTag("commit-graph").Test(c, func(f *fixtures.Fixture) {
+		dotgit := f.DotGit()
+
+		reader, err := mmap.Open(path.Join(dotgit.Root(), "objects", "info", "commit-graph"))
+		c.Assert(err, IsNil)
+		index, err := commitgraph.OpenFileIndex(reader)
+		c.Assert(err, IsNil)
+		memoryIndex := commitgraph.NewMemoryIndex()
+		for i, hash := range index.Hashes() {
+			node, err := index.GetNodeByIndex(i)
+			c.Assert(err, IsNil)
+			err = memoryIndex.Add(hash, node)
+			c.Assert(err, IsNil)
+		}
+		reader.Close()
+
+		writer, err := ioutil.TempFile(dotgit.Root(), "commit-graph")
+		c.Assert(err, IsNil)
+		tmpName := writer.Name()
+		defer os.Remove(tmpName)
+		encoder := commitgraph.NewEncoder(writer)
+		err = encoder.Encode(memoryIndex)
+		c.Assert(err, IsNil)
+		writer.Close()
+
+		testDecodeHelper(c, tmpName)
+	})
+}
diff --git a/plumbing/format/commitgraph/encoder.go b/plumbing/format/commitgraph/encoder.go
new file mode 100644
index 000000000..501b09e1c
--- /dev/null
+++ b/plumbing/format/commitgraph/encoder.go
@@ -0,0 +1,189 @@
+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}
+}
+
+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, largeEdgesCount := e.prepare(idx, hashes)
+
+	chunkSignatures := [][]byte{oidFanoutSignature, oidLookupSignature, commitDataSignature}
+	chunkSizes := []uint64{4 * 256, uint64(len(hashes)) * 20, uint64(len(hashes)) * 36}
+	if largeEdgesCount > 0 {
+		chunkSignatures = append(chunkSignatures, largeEdgeListSignature)
+		chunkSizes = append(chunkSizes, uint64(largeEdgesCount)*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 largeEdges, err := e.encodeCommitData(hashes, hashToIndex, idx); err == nil {
+		if err = e.encodeLargeEdges(largeEdges); 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, largeEdgesCount 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 large edge table
+	for i := 0; i < len(hashes); i++ {
+		v, _ := idx.GetNodeByIndex(i)
+		if len(v.ParentHashes) > 2 {
+			largeEdgesCount += 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) (largeEdges []uint32, err error) {
+	for _, hash := range hashes {
+		origIndex, _ := idx.GetIndexByHash(hash)
+		commitData, _ := idx.GetNodeByIndex(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(largeEdges)) | parentOctopusUsed
+			for _, parentHash := range commitData.ParentHashes[1:] {
+				largeEdges = append(largeEdges, hashToIndex[parentHash])
+			}
+			largeEdges[len(largeEdges)-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) encodeLargeEdges(largeEdges []uint32) (err error) {
+	for _, parent := range largeEdges {
+		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
+}
diff --git a/plumbing/format/commitgraph/file.go b/plumbing/format/commitgraph/file.go
new file mode 100644
index 000000000..dce62436c
--- /dev/null
+++ b/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("Unsuported 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("Unsuported 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'}
+	largeEdgeListSignature = []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
+	largeEdgeListOffset 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, largeEdgeListSignature) {
+			fi.largeEdgeListOffset = 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) GetNodeByIndex(idx int) (*Node, 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.largeEdgeListOffset + 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 &Node{
+		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
+}
diff --git a/plumbing/format/commitgraph/memory.go b/plumbing/format/commitgraph/memory.go
new file mode 100644
index 000000000..316bc6d57
--- /dev/null
+++ b/plumbing/format/commitgraph/memory.go
@@ -0,0 +1,71 @@
+package commitgraph
+
+import (
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+type MemoryIndex struct {
+	commitData []*Node
+	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
+}
+
+// GetNodeByIndex gets the commit node from the commit graph using index
+// obtained from child node, if available
+func (mi *MemoryIndex) GetNodeByIndex(i int) (*Node, error) {
+	if int(i) >= len(mi.commitData) {
+		return nil, plumbing.ErrObjectNotFound
+	}
+
+	node := mi.commitData[i]
+
+	// Map parent hashes to parent indexes
+	if node.ParentIndexes == nil {
+		parentIndexes := make([]int, len(node.ParentHashes))
+		for i, parentHash := range node.ParentHashes {
+			var err error
+			if parentIndexes[i], err = mi.GetIndexByHash(parentHash); err != nil {
+				return nil, err
+			}
+		}
+		node.ParentIndexes = parentIndexes
+	}
+
+	return node, 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, node *Node) error {
+	// The parent indexes are calculated lazily in GetNodeByIndex
+	// which allows adding nodes out of order as long as all parents
+	// are eventually resolved
+	node.ParentIndexes = nil
+	mi.indexMap[hash] = len(mi.commitData)
+	mi.commitData = append(mi.commitData, node)
+	return nil
+}