Merge branch 'pks-2pc-transaction-service' into 'master'

Implement reference transaction service

See merge request gitlab-org/gitaly!2077

10 files changed, 857 insertions, 0 deletions

diff --git a/changelogs/unreleased/pks-2pc-transaction-service.yml b/changelogs/unreleased/pks-2pc-transaction-service.yml
new file mode 100644
index 000000000..df56e7a8a
--- /dev/null
+++ b/changelogs/unreleased/pks-2pc-transaction-service.yml
@@ -0,0 +1,5 @@
+---
+title: Implement reference transaction service
+merge_request: 2077
+author:
+type: added
diff --git a/internal/praefect/server.go b/internal/praefect/server.go
index a29ce8e09..50af53059 100644
--- a/internal/praefect/server.go
+++ b/internal/praefect/server.go
@@ -24,6 +24,7 @@ import (
 	"gitlab.com/gitlab-org/gitaly/internal/praefect/protoregistry"
 	"gitlab.com/gitlab-org/gitaly/internal/praefect/service/info"
 	"gitlab.com/gitlab-org/gitaly/internal/praefect/service/server"
+	"gitlab.com/gitlab-org/gitaly/internal/praefect/service/transaction"
 	"gitlab.com/gitlab-org/gitaly/internal/server/auth"
 	"gitlab.com/gitlab-org/gitaly/proto/go/gitalypb"
 	grpccorrelation "gitlab.com/gitlab-org/labkit/correlation/grpc"
@@ -127,6 +128,7 @@ func (srv *Server) RegisterServices(nm nodes.Manager, conf config.Config, ds dat
 	// ServerServiceServer is necessary for the ServerInfo RPC
 	gitalypb.RegisterServerServiceServer(srv.s, server.NewServer(conf, nm))
 	gitalypb.RegisterPraefectInfoServiceServer(srv.s, info.NewServer(nm, conf, ds))
+	gitalypb.RegisterRefTransactionServer(srv.s, transaction.NewServer())
 	healthpb.RegisterHealthServer(srv.s, health.NewServer())
 
 	grpc_prometheus.Register(srv.s)
diff --git a/internal/praefect/service/transaction/server.go b/internal/praefect/service/transaction/server.go
new file mode 100644
index 000000000..aa17eee9f
--- /dev/null
+++ b/internal/praefect/service/transaction/server.go
@@ -0,0 +1,99 @@
+package transaction
+
+import (
+	"context"
+	"crypto/sha1"
+	"fmt"
+	"math/rand"
+	"sync"
+
+	"gitlab.com/gitlab-org/gitaly/internal/helper"
+	"gitlab.com/gitlab-org/gitaly/proto/go/gitalypb"
+)
+
+type Server struct {
+	gitalypb.UnimplementedRefTransactionServer
+
+	lock         sync.Mutex
+	transactions map[uint64]string
+}
+
+func NewServer() gitalypb.RefTransactionServer {
+	return &Server{
+		transactions: make(map[uint64]string),
+	}
+}
+
+// RegisterTransaction registers a new reference transaction for a set of nodes
+// taking part in the transaction.
+func (s *Server) RegisterTransaction(ctx context.Context, in *gitalypb.RegisterTransactionRequest) (*gitalypb.RegisterTransactionResponse, error) {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+
+	transactionID := rand.Uint64()
+	if _, ok := s.transactions[transactionID]; ok {
+		return nil, helper.ErrInternalf("transaction exists already")
+	}
+
+	// We only accept a single node in transactions right now, which is
+	// usually the primary. This limitation will be lifted at a later point
+	// to allow for real transaction voting and multi-phase commits.
+	if len(in.Nodes) != 1 {
+		return nil, helper.ErrInvalidArgumentf("transaction requires exactly one node")
+	}
+	s.transactions[transactionID] = in.Nodes[0]
+
+	return &gitalypb.RegisterTransactionResponse{
+		TransactionId: transactionID,
+	}, nil
+}
+
+// StartTransaction is called by a client who's starting a reference
+// transaction. As we currently only have primary nodes which perform reference
+// transactions, this RPC doesn't yet do anything of interest but will
+// immediately return "COMMIT". In future, the RPC will wait for all clients of
+// a given transaction to start the transaction and perform a vote.
+func (s *Server) StartTransaction(ctx context.Context, in *gitalypb.StartTransactionRequest) (*gitalypb.StartTransactionResponse, error) {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+
+	// While the reference updates hash is not used yet, we already verify
+	// it's there. At a later point, the hash will be used to verify that
+	// all voting nodes agree on the same updates.
+	if len(in.ReferenceUpdatesHash) != sha1.Size {
+		return nil, helper.ErrInvalidArgumentf("invalid reference hash: %q", in.ReferenceUpdatesHash)
+	}
+
+	transaction, ok := s.transactions[in.TransactionId]
+	if !ok {
+		return nil, helper.ErrNotFound(fmt.Errorf("no such transaction: %d", in.TransactionId))
+	}
+
+	if transaction != in.Node {
+		return nil, helper.ErrInternalf("invalid node for transaction: %q", in.Node)
+	}
+
+	// Currently, only the primary node will perform transactions. We can
+	// thus just delete the transaction as soon as it starts the
+	// transaction and instruct it to commit.
+	delete(s.transactions, in.TransactionId)
+
+	return &gitalypb.StartTransactionResponse{
+		State: gitalypb.StartTransactionResponse_COMMIT,
+	}, nil
+}
+
+// CancelTransaction cancels a registered transaction, removing all data
+// associated with it.
+func (s *Server) CancelTransaction(ctx context.Context, in *gitalypb.CancelTransactionRequest) (*gitalypb.CancelTransactionResponse, error) {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+
+	_, ok := s.transactions[in.TransactionId]
+	if !ok {
+		return nil, helper.ErrNotFound(fmt.Errorf("no such transaction: %d", in.TransactionId))
+	}
+	delete(s.transactions, in.TransactionId)
+
+	return &gitalypb.CancelTransactionResponse{}, nil
+}
diff --git a/internal/praefect/transaction_test.go b/internal/praefect/transaction_test.go
new file mode 100644
index 000000000..ded0a8425
--- /dev/null
+++ b/internal/praefect/transaction_test.go
@@ -0,0 +1,88 @@
+package praefect
+
+import (
+	"context"
+	"crypto/sha1"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"gitlab.com/gitlab-org/gitaly/proto/go/gitalypb"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+func TestTransactionSucceeds(t *testing.T) {
+	cc, _, cleanup := runPraefectServerWithGitaly(t, testConfig(1))
+	defer cleanup()
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+
+	client := gitalypb.NewRefTransactionClient(cc)
+
+	registration, err := client.RegisterTransaction(ctx, &gitalypb.RegisterTransactionRequest{
+		Nodes: []string{"node1"},
+	})
+	require.NoError(t, err)
+	require.NotZero(t, registration.TransactionId)
+
+	hash := sha1.Sum([]byte{})
+
+	response, err := client.StartTransaction(ctx, &gitalypb.StartTransactionRequest{
+		TransactionId:        registration.TransactionId,
+		Node:                 "node1",
+		ReferenceUpdatesHash: hash[:],
+	})
+	require.NoError(t, err)
+	require.Equal(t, gitalypb.StartTransactionResponse_COMMIT, response.State)
+}
+
+func TestTransactionFailures(t *testing.T) {
+	cc, _, cleanup := runPraefectServerWithGitaly(t, testConfig(1))
+	defer cleanup()
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+
+	client := gitalypb.NewRefTransactionClient(cc)
+
+	hash := sha1.Sum([]byte{})
+	_, err := client.StartTransaction(ctx, &gitalypb.StartTransactionRequest{
+		TransactionId:        1,
+		Node:                 "node1",
+		ReferenceUpdatesHash: hash[:],
+	})
+	require.Error(t, err)
+	require.Equal(t, codes.NotFound, status.Code(err))
+}
+
+func TestTransactionCancellation(t *testing.T) {
+	cc, _, cleanup := runPraefectServerWithGitaly(t, testConfig(1))
+	defer cleanup()
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+
+	client := gitalypb.NewRefTransactionClient(cc)
+
+	registration, err := client.RegisterTransaction(ctx, &gitalypb.RegisterTransactionRequest{
+		Nodes: []string{"node1"},
+	})
+	require.NoError(t, err)
+	require.NotZero(t, registration.TransactionId)
+
+	_, err = client.CancelTransaction(ctx, &gitalypb.CancelTransactionRequest{
+		TransactionId: registration.TransactionId,
+	})
+	require.NoError(t, err)
+
+	hash := sha1.Sum([]byte{})
+	_, err = client.StartTransaction(ctx, &gitalypb.StartTransactionRequest{
+		TransactionId:        registration.TransactionId,
+		Node:                 "node1",
+		ReferenceUpdatesHash: hash[:],
+	})
+	require.Error(t, err)
+	require.Equal(t, codes.NotFound, status.Code(err))
+}
diff --git a/proto/go/gitalypb/protolist.go b/proto/go/gitalypb/protolist.go
index d2b27af02..a15916f70 100644
--- a/proto/go/gitalypb/protolist.go
+++ b/proto/go/gitalypb/protolist.go
@@ -23,5 +23,6 @@ var GitalyProtos = []string{
 	"shared.proto",
 	"smarthttp.proto",
 	"ssh.proto",
+	"transaction.proto",
 	"wiki.proto",
 }
diff --git a/proto/go/gitalypb/transaction.pb.go b/proto/go/gitalypb/transaction.pb.go
new file mode 100644
index 000000000..59cf4085e
--- /dev/null
+++ b/proto/go/gitalypb/transaction.pb.go
@@ -0,0 +1,519 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// source: transaction.proto
+
+package gitalypb
+
+import (
+	context "context"
+	fmt "fmt"
+	proto "github.com/golang/protobuf/proto"
+	grpc "google.golang.org/grpc"
+	codes "google.golang.org/grpc/codes"
+	status "google.golang.org/grpc/status"
+	math "math"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.ProtoPackageIsVersion3 // please upgrade the proto package
+
+// The outcome of the given transaction telling the client whether the
+// transaction should be committed or rolled back.
+type StartTransactionResponse_TransactionState int32
+
+const (
+	StartTransactionResponse_COMMIT StartTransactionResponse_TransactionState = 0
+	StartTransactionResponse_ABORT  StartTransactionResponse_TransactionState = 1
+)
+
+var StartTransactionResponse_TransactionState_name = map[int32]string{
+	0: "COMMIT",
+	1: "ABORT",
+}
+
+var StartTransactionResponse_TransactionState_value = map[string]int32{
+	"COMMIT": 0,
+	"ABORT":  1,
+}
+
+func (x StartTransactionResponse_TransactionState) String() string {
+	return proto.EnumName(StartTransactionResponse_TransactionState_name, int32(x))
+}
+
+func (StartTransactionResponse_TransactionState) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_2cc4e03d2c28c490, []int{3, 0}
+}
+
+type RegisterTransactionRequest struct {
+	Repository *Repository `protobuf:"bytes,1,opt,name=repository,proto3" json:"repository,omitempty"`
+	// Nodes taking part in the transaction
+	Nodes                []string `protobuf:"bytes,2,rep,name=nodes,proto3" json:"nodes,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *RegisterTransactionRequest) Reset()         { *m = RegisterTransactionRequest{} }
+func (m *RegisterTransactionRequest) String() string { return proto.CompactTextString(m) }
+func (*RegisterTransactionRequest) ProtoMessage()    {}
+func (*RegisterTransactionRequest) Descriptor() ([]byte, []int) {
+	return fileDescriptor_2cc4e03d2c28c490, []int{0}
+}
+
+func (m *RegisterTransactionRequest) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_RegisterTransactionRequest.Unmarshal(m, b)
+}
+func (m *RegisterTransactionRequest) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_RegisterTransactionRequest.Marshal(b, m, deterministic)
+}
+func (m *RegisterTransactionRequest) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_RegisterTransactionRequest.Merge(m, src)
+}
+func (m *RegisterTransactionRequest) XXX_Size() int {
+	return xxx_messageInfo_RegisterTransactionRequest.Size(m)
+}
+func (m *RegisterTransactionRequest) XXX_DiscardUnknown() {
+	xxx_messageInfo_RegisterTransactionRequest.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_RegisterTransactionRequest proto.InternalMessageInfo
+
+func (m *RegisterTransactionRequest) GetRepository() *Repository {
+	if m != nil {
+		return m.Repository
+	}
+	return nil
+}
+
+func (m *RegisterTransactionRequest) GetNodes() []string {
+	if m != nil {
+		return m.Nodes
+	}
+	return nil
+}
+
+type RegisterTransactionResponse struct {
+	TransactionId        uint64   `protobuf:"varint,1,opt,name=transaction_id,json=transactionId,proto3" json:"transaction_id,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *RegisterTransactionResponse) Reset()         { *m = RegisterTransactionResponse{} }
+func (m *RegisterTransactionResponse) String() string { return proto.CompactTextString(m) }
+func (*RegisterTransactionResponse) ProtoMessage()    {}
+func (*RegisterTransactionResponse) Descriptor() ([]byte, []int) {
+	return fileDescriptor_2cc4e03d2c28c490, []int{1}
+}
+
+func (m *RegisterTransactionResponse) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_RegisterTransactionResponse.Unmarshal(m, b)
+}
+func (m *RegisterTransactionResponse) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_RegisterTransactionResponse.Marshal(b, m, deterministic)
+}
+func (m *RegisterTransactionResponse) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_RegisterTransactionResponse.Merge(m, src)
+}
+func (m *RegisterTransactionResponse) XXX_Size() int {
+	return xxx_messageInfo_RegisterTransactionResponse.Size(m)
+}
+func (m *RegisterTransactionResponse) XXX_DiscardUnknown() {
+	xxx_messageInfo_RegisterTransactionResponse.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_RegisterTransactionResponse proto.InternalMessageInfo
+
+func (m *RegisterTransactionResponse) GetTransactionId() uint64 {
+	if m != nil {
+		return m.TransactionId
+	}
+	return 0
+}
+
+type StartTransactionRequest struct {
+	Repository *Repository `protobuf:"bytes,1,opt,name=repository,proto3" json:"repository,omitempty"`
+	// ID of the transaction we're processing
+	TransactionId uint64 `protobuf:"varint,2,opt,name=transaction_id,json=transactionId,proto3" json:"transaction_id,omitempty"`
+	// Name of the Gitaly node that's starting a transaction.
+	Node string `protobuf:"bytes,3,opt,name=node,proto3" json:"node,omitempty"`
+	// SHA1 of the references that are to be updated
+	ReferenceUpdatesHash []byte   `protobuf:"bytes,4,opt,name=reference_updates_hash,json=referenceUpdatesHash,proto3" json:"reference_updates_hash,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *StartTransactionRequest) Reset()         { *m = StartTransactionRequest{} }
+func (m *StartTransactionRequest) String() string { return proto.CompactTextString(m) }
+func (*StartTransactionRequest) ProtoMessage()    {}
+func (*StartTransactionRequest) Descriptor() ([]byte, []int) {
+	return fileDescriptor_2cc4e03d2c28c490, []int{2}
+}
+
+func (m *StartTransactionRequest) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_StartTransactionRequest.Unmarshal(m, b)
+}
+func (m *StartTransactionRequest) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_StartTransactionRequest.Marshal(b, m, deterministic)
+}
+func (m *StartTransactionRequest) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_StartTransactionRequest.Merge(m, src)
+}
+func (m *StartTransactionRequest) XXX_Size() int {
+	return xxx_messageInfo_StartTransactionRequest.Size(m)
+}
+func (m *StartTransactionRequest) XXX_DiscardUnknown() {
+	xxx_messageInfo_StartTransactionRequest.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_StartTransactionRequest proto.InternalMessageInfo
+
+func (m *StartTransactionRequest) GetRepository() *Repository {
+	if m != nil {
+		return m.Repository
+	}
+	return nil
+}
+
+func (m *StartTransactionRequest) GetTransactionId() uint64 {
+	if m != nil {
+		return m.TransactionId
+	}
+	return 0
+}
+
+func (m *StartTransactionRequest) GetNode() string {
+	if m != nil {
+		return m.Node
+	}
+	return ""
+}
+
+func (m *StartTransactionRequest) GetReferenceUpdatesHash() []byte {
+	if m != nil {
+		return m.ReferenceUpdatesHash
+	}
+	return nil
+}
+
+type StartTransactionResponse struct {
+	State                StartTransactionResponse_TransactionState `protobuf:"varint,1,opt,name=state,proto3,enum=gitaly.StartTransactionResponse_TransactionState" json:"state,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}                                  `json:"-"`
+	XXX_unrecognized     []byte                                    `json:"-"`
+	XXX_sizecache        int32                                     `json:"-"`
+}
+
+func (m *StartTransactionResponse) Reset()         { *m = StartTransactionResponse{} }
+func (m *StartTransactionResponse) String() string { return proto.CompactTextString(m) }
+func (*StartTransactionResponse) ProtoMessage()    {}
+func (*StartTransactionResponse) Descriptor() ([]byte, []int) {
+	return fileDescriptor_2cc4e03d2c28c490, []int{3}
+}
+
+func (m *StartTransactionResponse) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_StartTransactionResponse.Unmarshal(m, b)
+}
+func (m *StartTransactionResponse) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_StartTransactionResponse.Marshal(b, m, deterministic)
+}
+func (m *StartTransactionResponse) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_StartTransactionResponse.Merge(m, src)
+}
+func (m *StartTransactionResponse) XXX_Size() int {
+	return xxx_messageInfo_StartTransactionResponse.Size(m)
+}
+func (m *StartTransactionResponse) XXX_DiscardUnknown() {
+	xxx_messageInfo_StartTransactionResponse.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_StartTransactionResponse proto.InternalMessageInfo
+
+func (m *StartTransactionResponse) GetState() StartTransactionResponse_TransactionState {
+	if m != nil {
+		return m.State
+	}
+	return StartTransactionResponse_COMMIT
+}
+
+type CancelTransactionRequest struct {
+	Repository *Repository `protobuf:"bytes,1,opt,name=repository,proto3" json:"repository,omitempty"`
+	// ID of the transaction we're about to cancel
+	TransactionId        uint64   `protobuf:"varint,2,opt,name=transaction_id,json=transactionId,proto3" json:"transaction_id,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *CancelTransactionRequest) Reset()         { *m = CancelTransactionRequest{} }
+func (m *CancelTransactionRequest) String() string { return proto.CompactTextString(m) }
+func (*CancelTransactionRequest) ProtoMessage()    {}
+func (*CancelTransactionRequest) Descriptor() ([]byte, []int) {
+	return fileDescriptor_2cc4e03d2c28c490, []int{4}
+}
+
+func (m *CancelTransactionRequest) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_CancelTransactionRequest.Unmarshal(m, b)
+}
+func (m *CancelTransactionRequest) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_CancelTransactionRequest.Marshal(b, m, deterministic)
+}
+func (m *CancelTransactionRequest) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_CancelTransactionRequest.Merge(m, src)
+}
+func (m *CancelTransactionRequest) XXX_Size() int {
+	return xxx_messageInfo_CancelTransactionRequest.Size(m)
+}
+func (m *CancelTransactionRequest) XXX_DiscardUnknown() {
+	xxx_messageInfo_CancelTransactionRequest.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_CancelTransactionRequest proto.InternalMessageInfo
+
+func (m *CancelTransactionRequest) GetRepository() *Repository {
+	if m != nil {
+		return m.Repository
+	}
+	return nil
+}
+
+func (m *CancelTransactionRequest) GetTransactionId() uint64 {
+	if m != nil {
+		return m.TransactionId
+	}
+	return 0
+}
+
+type CancelTransactionResponse struct {
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *CancelTransactionResponse) Reset()         { *m = CancelTransactionResponse{} }
+func (m *CancelTransactionResponse) String() string { return proto.CompactTextString(m) }
+func (*CancelTransactionResponse) ProtoMessage()    {}
+func (*CancelTransactionResponse) Descriptor() ([]byte, []int) {
+	return fileDescriptor_2cc4e03d2c28c490, []int{5}
+}
+
+func (m *CancelTransactionResponse) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_CancelTransactionResponse.Unmarshal(m, b)
+}
+func (m *CancelTransactionResponse) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_CancelTransactionResponse.Marshal(b, m, deterministic)
+}
+func (m *CancelTransactionResponse) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_CancelTransactionResponse.Merge(m, src)
+}
+func (m *CancelTransactionResponse) XXX_Size() int {
+	return xxx_messageInfo_CancelTransactionResponse.Size(m)
+}
+func (m *CancelTransactionResponse) XXX_DiscardUnknown() {
+	xxx_messageInfo_CancelTransactionResponse.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_CancelTransactionResponse proto.InternalMessageInfo
+
+func init() {
+	proto.RegisterEnum("gitaly.StartTransactionResponse_TransactionState", StartTransactionResponse_TransactionState_name, StartTransactionResponse_TransactionState_value)
+	proto.RegisterType((*RegisterTransactionRequest)(nil), "gitaly.RegisterTransactionRequest")
+	proto.RegisterType((*RegisterTransactionResponse)(nil), "gitaly.RegisterTransactionResponse")
+	proto.RegisterType((*StartTransactionRequest)(nil), "gitaly.StartTransactionRequest")
+	proto.RegisterType((*StartTransactionResponse)(nil), "gitaly.StartTransactionResponse")
+	proto.RegisterType((*CancelTransactionRequest)(nil), "gitaly.CancelTransactionRequest")
+	proto.RegisterType((*CancelTransactionResponse)(nil), "gitaly.CancelTransactionResponse")
+}
+
+func init() { proto.RegisterFile("transaction.proto", fileDescriptor_2cc4e03d2c28c490) }
+
+var fileDescriptor_2cc4e03d2c28c490 = []byte{
+	// 439 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xc4, 0x54, 0xc1, 0x6e, 0xd3, 0x40,
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+	0x7c, 0x14, 0x27, 0x14, 0x6f, 0x71, 0x4d, 0x63, 0x97, 0x0b, 0x12, 0xb7, 0x9d, 0x79, 0xf3, 0xe6,
+	0xed, 0x9b, 0x59, 0x2d, 0xec, 0x18, 0x25, 0x0a, 0x2d, 0x22, 0x93, 0xc9, 0x22, 0x28, 0x95, 0x34,
+	0x92, 0x0e, 0x93, 0xcc, 0x88, 0xfc, 0xd4, 0x85, 0x3c, 0x2b, 0x8c, 0xcd, 0xb9, 0xdb, 0x3a, 0x15,
+	0x0a, 0x63, 0x1b, 0xb1, 0x1c, 0x5c, 0x8e, 0x49, 0xa6, 0x0d, 0xaa, 0xf9, 0x39, 0x9d, 0xe3, 0xc7,
+	0x13, 0xd4, 0x86, 0x3e, 0x07, 0x50, 0x58, 0x4a, 0x9d, 0x19, 0xa9, 0x4e, 0x1d, 0xe2, 0x11, 0xff,
+	0xda, 0x94, 0x06, 0xb6, 0x69, 0xc0, 0x6b, 0x64, 0xd6, 0xff, 0xfa, 0xe3, 0x21, 0xe1, 0x8d, 0x5a,
+	0xba, 0x0b, 0x83, 0x42, 0xc6, 0xa8, 0x9d, 0x9e, 0xb7, 0xe5, 0x8f, 0xb8, 0x0d, 0xd8, 0x4b, 0xd8,
+	0x6b, 0x55, 0xd3, 0xa5, 0x2c, 0x34, 0xd2, 0xfb, 0x30, 0x6e, 0x78, 0x58, 0x64, 0x71, 0x25, 0xd9,
+	0xe7, 0xd7, 0x1b, 0xd9, 0x83, 0x98, 0x7d, 0x27, 0x70, 0xeb, 0xd8, 0x08, 0x65, 0xfe, 0xe9, 0x8d,
+	0x37, 0xc5, 0x7b, 0x2d, 0xe2, 0x94, 0x42, 0x7f, 0xed, 0xc5, 0xd9, 0xf2, 0x88, 0x3f, 0xe2, 0xd5,
+	0x99, 0x3e, 0x83, 0x9b, 0x0a, 0x57, 0xa8, 0xb0, 0x88, 0x70, 0x71, 0x52, 0xc6, 0xc2, 0xa0, 0x5e,
+	0xa4, 0x42, 0xa7, 0x4e, 0xdf, 0x23, 0xfe, 0x36, 0xdf, 0xad, 0xd1, 0x37, 0x16, 0x7c, 0x2d, 0x74,
+	0xca, 0x3e, 0x13, 0x70, 0x36, 0x6d, 0x9c, 0x8d, 0xe2, 0x15, 0x0c, 0xb4, 0x11, 0x06, 0x2b, 0x0b,
+	0xe3, 0xe9, 0x93, 0xdf, 0x16, 0xba, 0x08, 0x41, 0x23, 0x77, 0xbc, 0x26, 0x72, 0xcb, 0x67, 0x0f,
+	0x60, 0x72, 0x11, 0xa2, 0x00, 0xc3, 0xfd, 0xa3, 0xc3, 0xc3, 0x83, 0xf9, 0xe4, 0x0a, 0x1d, 0xc1,
+	0xe0, 0xc5, 0xec, 0x88, 0xcf, 0x27, 0x84, 0x7d, 0x02, 0x67, 0x5f, 0x14, 0x11, 0xe6, 0xff, 0x61,
+	0xae, 0x6c, 0x0f, 0x6e, 0xb7, 0x88, 0x5b, 0x73, 0xd3, 0x6f, 0x3d, 0x18, 0x73, 0x5c, 0x35, 0x20,
+	0xba, 0x82, 0x1b, 0x2d, 0x4f, 0x89, 0xb2, 0xf3, 0x3b, 0x75, 0xbd, 0x6a, 0xf7, 0xde, 0xa5, 0x35,
+	0x56, 0x92, 0x0d, 0x7f, 0x7e, 0xf1, 0x7b, 0x57, 0x09, 0x7d, 0x07, 0x93, 0x8b, 0x33, 0xa7, 0x77,
+	0xba, 0xb7, 0x61, 0x15, 0xbc, 0xbf, 0xad, 0xab, 0x6e, 0xff, 0x1e, 0x76, 0x36, 0x6c, 0xd3, 0x9a,
+	0xde, 0xb5, 0x0e, 0xf7, 0xee, 0x25, 0x15, 0x7f, 0x2a, 0xcc, 0x1e, 0xbf, 0x5d, 0xd7, 0xe6, 0x62,
+	0x19, 0x44, 0xf2, 0x43, 0x68, 0x8f, 0x8f, 0xa4, 0x4a, 0x42, 0xdb, 0x21, 0xac, 0xfe, 0x81, 0x30,
+	0x91, 0x67, 0x71, 0xb9, 0x5c, 0x0e, 0xab, 0xd4, 0xd3, 0x5f, 0x01, 0x00, 0x00, 0xff, 0xff, 0x77,
+	0xd4, 0x86, 0x22, 0x51, 0x04, 0x00, 0x00,
+}
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ context.Context
+var _ grpc.ClientConn
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the grpc package it is being compiled against.
+const _ = grpc.SupportPackageIsVersion4
+
+// RefTransactionClient is the client API for RefTransaction service.
+//
+// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://godoc.org/google.golang.org/grpc#ClientConn.NewStream.
+type RefTransactionClient interface {
+	RegisterTransaction(ctx context.Context, in *RegisterTransactionRequest, opts ...grpc.CallOption) (*RegisterTransactionResponse, error)
+	StartTransaction(ctx context.Context, in *StartTransactionRequest, opts ...grpc.CallOption) (*StartTransactionResponse, error)
+	CancelTransaction(ctx context.Context, in *CancelTransactionRequest, opts ...grpc.CallOption) (*CancelTransactionResponse, error)
+}
+
+type refTransactionClient struct {
+	cc *grpc.ClientConn
+}
+
+func NewRefTransactionClient(cc *grpc.ClientConn) RefTransactionClient {
+	return &refTransactionClient{cc}
+}
+
+func (c *refTransactionClient) RegisterTransaction(ctx context.Context, in *RegisterTransactionRequest, opts ...grpc.CallOption) (*RegisterTransactionResponse, error) {
+	out := new(RegisterTransactionResponse)
+	err := c.cc.Invoke(ctx, "/gitaly.RefTransaction/RegisterTransaction", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *refTransactionClient) StartTransaction(ctx context.Context, in *StartTransactionRequest, opts ...grpc.CallOption) (*StartTransactionResponse, error) {
+	out := new(StartTransactionResponse)
+	err := c.cc.Invoke(ctx, "/gitaly.RefTransaction/StartTransaction", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *refTransactionClient) CancelTransaction(ctx context.Context, in *CancelTransactionRequest, opts ...grpc.CallOption) (*CancelTransactionResponse, error) {
+	out := new(CancelTransactionResponse)
+	err := c.cc.Invoke(ctx, "/gitaly.RefTransaction/CancelTransaction", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+// RefTransactionServer is the server API for RefTransaction service.
+type RefTransactionServer interface {
+	RegisterTransaction(context.Context, *RegisterTransactionRequest) (*RegisterTransactionResponse, error)
+	StartTransaction(context.Context, *StartTransactionRequest) (*StartTransactionResponse, error)
+	CancelTransaction(context.Context, *CancelTransactionRequest) (*CancelTransactionResponse, error)
+}
+
+// UnimplementedRefTransactionServer can be embedded to have forward compatible implementations.
+type UnimplementedRefTransactionServer struct {
+}
+
+func (*UnimplementedRefTransactionServer) RegisterTransaction(ctx context.Context, req *RegisterTransactionRequest) (*RegisterTransactionResponse, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method RegisterTransaction not implemented")
+}
+func (*UnimplementedRefTransactionServer) StartTransaction(ctx context.Context, req *StartTransactionRequest) (*StartTransactionResponse, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method StartTransaction not implemented")
+}
+func (*UnimplementedRefTransactionServer) CancelTransaction(ctx context.Context, req *CancelTransactionRequest) (*CancelTransactionResponse, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method CancelTransaction not implemented")
+}
+
+func RegisterRefTransactionServer(s *grpc.Server, srv RefTransactionServer) {
+	s.RegisterService(&_RefTransaction_serviceDesc, srv)
+}
+
+func _RefTransaction_RegisterTransaction_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(RegisterTransactionRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(RefTransactionServer).RegisterTransaction(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/gitaly.RefTransaction/RegisterTransaction",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(RefTransactionServer).RegisterTransaction(ctx, req.(*RegisterTransactionRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _RefTransaction_StartTransaction_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(StartTransactionRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(RefTransactionServer).StartTransaction(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/gitaly.RefTransaction/StartTransaction",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(RefTransactionServer).StartTransaction(ctx, req.(*StartTransactionRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _RefTransaction_CancelTransaction_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(CancelTransactionRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(RefTransactionServer).CancelTransaction(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/gitaly.RefTransaction/CancelTransaction",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(RefTransactionServer).CancelTransaction(ctx, req.(*CancelTransactionRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+var _RefTransaction_serviceDesc = grpc.ServiceDesc{
+	ServiceName: "gitaly.RefTransaction",
+	HandlerType: (*RefTransactionServer)(nil),
+	Methods: []grpc.MethodDesc{
+		{
+			MethodName: "RegisterTransaction",
+			Handler:    _RefTransaction_RegisterTransaction_Handler,
+		},
+		{
+			MethodName: "StartTransaction",
+			Handler:    _RefTransaction_StartTransaction_Handler,
+		},
+		{
+			MethodName: "CancelTransaction",
+			Handler:    _RefTransaction_CancelTransaction_Handler,
+		},
+	},
+	Streams:  []grpc.StreamDesc{},
+	Metadata: "transaction.proto",
+}
diff --git a/proto/transaction.proto b/proto/transaction.proto
new file mode 100644
index 000000000..645833b2d
--- /dev/null
+++ b/proto/transaction.proto
@@ -0,0 +1,72 @@
+syntax = "proto3";
+
+package gitaly;
+
+option go_package = "gitlab.com/gitlab-org/gitaly/proto/go/gitalypb";
+
+import "lint.proto";
+import "shared.proto";
+
+service RefTransaction {
+
+  rpc RegisterTransaction (RegisterTransactionRequest) returns (RegisterTransactionResponse) {
+    option (op_type) = {
+      op:          MUTATOR
+      scope_level: REPOSITORY
+    };
+  }
+
+  rpc StartTransaction (StartTransactionRequest) returns (StartTransactionResponse) {
+    option (op_type) = {
+      op:          MUTATOR
+      scope_level: REPOSITORY
+    };
+  }
+
+  rpc CancelTransaction (CancelTransactionRequest) returns (CancelTransactionResponse) {
+    option (op_type) = {
+      op:          MUTATOR
+      scope_level: REPOSITORY
+    };
+  }
+
+}
+
+message RegisterTransactionRequest {
+  Repository repository = 1[(target_repository)=true];
+  // Nodes taking part in the transaction
+  repeated string nodes = 2;
+}
+
+message RegisterTransactionResponse {
+  uint64 transaction_id = 1;
+}
+
+message StartTransactionRequest {
+  Repository repository = 1[(target_repository)=true];
+  // ID of the transaction we're processing
+  uint64 transaction_id = 2;
+  // Name of the Gitaly node that's starting a transaction.
+  string node = 3;
+  // SHA1 of the references that are to be updated
+  bytes reference_updates_hash = 4;
+}
+
+message StartTransactionResponse {
+  // The outcome of the given transaction telling the client whether the
+  // transaction should be committed or rolled back.
+  enum TransactionState {
+    COMMIT = 0;
+    ABORT = 1;
+  }
+
+  TransactionState state = 1;
+}
+
+message CancelTransactionRequest {
+  Repository repository = 1[(target_repository)=true];
+  // ID of the transaction we're about to cancel
+  uint64 transaction_id = 2;
+}
+
+message CancelTransactionResponse {}
diff --git a/ruby/proto/gitaly.rb b/ruby/proto/gitaly.rb
index 8674ab879..9c80cea63 100644
--- a/ruby/proto/gitaly.rb
+++ b/ruby/proto/gitaly.rb
@@ -37,5 +37,7 @@ require 'gitaly/smarthttp_services_pb'
 
 require 'gitaly/ssh_services_pb'
 
+require 'gitaly/transaction_services_pb'
+
 require 'gitaly/wiki_services_pb'
 
diff --git a/ruby/proto/gitaly/transaction_pb.rb b/ruby/proto/gitaly/transaction_pb.rb
new file mode 100644
index 000000000..c3d9d0ad6
--- /dev/null
+++ b/ruby/proto/gitaly/transaction_pb.rb
@@ -0,0 +1,45 @@
+# Generated by the protocol buffer compiler.  DO NOT EDIT!
+# source: transaction.proto
+
+require 'google/protobuf'
+
+require 'lint_pb'
+require 'shared_pb'
+Google::Protobuf::DescriptorPool.generated_pool.build do
+  add_message "gitaly.RegisterTransactionRequest" do
+    optional :repository, :message, 1, "gitaly.Repository"
+    repeated :nodes, :string, 2
+  end
+  add_message "gitaly.RegisterTransactionResponse" do
+    optional :transaction_id, :uint64, 1
+  end
+  add_message "gitaly.StartTransactionRequest" do
+    optional :repository, :message, 1, "gitaly.Repository"
+    optional :transaction_id, :uint64, 2
+    optional :node, :string, 3
+    optional :reference_updates_hash, :bytes, 4
+  end
+  add_message "gitaly.StartTransactionResponse" do
+    optional :state, :enum, 1, "gitaly.StartTransactionResponse.TransactionState"
+  end
+  add_enum "gitaly.StartTransactionResponse.TransactionState" do
+    value :COMMIT, 0
+    value :ABORT, 1
+  end
+  add_message "gitaly.CancelTransactionRequest" do
+    optional :repository, :message, 1, "gitaly.Repository"
+    optional :transaction_id, :uint64, 2
+  end
+  add_message "gitaly.CancelTransactionResponse" do
+  end
+end
+
+module Gitaly
+  RegisterTransactionRequest = Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.RegisterTransactionRequest").msgclass
+  RegisterTransactionResponse = Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.RegisterTransactionResponse").msgclass
+  StartTransactionRequest = Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.StartTransactionRequest").msgclass
+  StartTransactionResponse = Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.StartTransactionResponse").msgclass
+  StartTransactionResponse::TransactionState = Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.StartTransactionResponse.TransactionState").enummodule
+  CancelTransactionRequest = Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.CancelTransactionRequest").msgclass
+  CancelTransactionResponse = Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.CancelTransactionResponse").msgclass
+end
diff --git a/ruby/proto/gitaly/transaction_services_pb.rb b/ruby/proto/gitaly/transaction_services_pb.rb
new file mode 100644
index 000000000..b465426ec
--- /dev/null
+++ b/ruby/proto/gitaly/transaction_services_pb.rb
@@ -0,0 +1,24 @@
+# Generated by the protocol buffer compiler.  DO NOT EDIT!
+# Source: transaction.proto for package 'gitaly'
+
+require 'grpc'
+require 'transaction_pb'
+
+module Gitaly
+  module RefTransaction
+    class Service
+
+      include GRPC::GenericService
+
+      self.marshal_class_method = :encode
+      self.unmarshal_class_method = :decode
+      self.service_name = 'gitaly.RefTransaction'
+
+      rpc :RegisterTransaction, RegisterTransactionRequest, RegisterTransactionResponse
+      rpc :StartTransaction, StartTransactionRequest, StartTransactionResponse
+      rpc :CancelTransaction, CancelTransactionRequest, CancelTransactionResponse
+    end
+
+    Stub = Service.rpc_stub_class
+  end
+end