etcdserver: add snapshotStore and raftStorage

snapshotStore is the store of snapshot, and it supports to get latest snapshot
and save incoming snapshot.

raftStorage supports to get latest snapshot when v3demo is open.

etcdserver/raft.go

@@ -103,7 +103,7 @@ type raftNode struct {
 
 	// utility
 	ticker      <-chan time.Time
-	raftStorage *raft.MemoryStorage
+	raftStorage *raftStorage
 	storage     Storage
 	// transport specifies the transport to send and receive msgs to members.
 	// Sending messages MUST NOT block. It is okay to drop messages, since
@@ -238,7 +238,7 @@ func advanceTicksForElection(n raft.Node, electionTicks int) {
 	}
 }
 
-func startNode(cfg *ServerConfig, cl *cluster, ids []types.ID) (id types.ID, n raft.Node, s *raft.MemoryStorage, w *wal.WAL) {
+func startNode(cfg *ServerConfig, cl *cluster, ids []types.ID) (id types.ID, n raft.Node, s *raftStorage, w *wal.WAL) {
 	var err error
 	member := cl.MemberByName(cfg.Name)
 	metadata := pbutil.MustMarshal(
@@ -263,7 +263,7 @@ func startNode(cfg *ServerConfig, cl *cluster, ids []types.ID) (id types.ID, n r
 	}
 	id = member.ID
 	plog.Infof("starting member %s in cluster %s", id, cl.ID())
-	s = raft.NewMemoryStorage()
+	s = newRaftStorage()
 	c := &raft.Config{
 		ID:              uint64(id),
 		ElectionTick:    cfg.ElectionTicks,
@@ -278,7 +278,7 @@ func startNode(cfg *ServerConfig, cl *cluster, ids []types.ID) (id types.ID, n r
 	return
 }
 
-func restartNode(cfg *ServerConfig, snapshot *raftpb.Snapshot) (types.ID, *cluster, raft.Node, *raft.MemoryStorage, *wal.WAL) {
+func restartNode(cfg *ServerConfig, snapshot *raftpb.Snapshot) (types.ID, *cluster, raft.Node, *raftStorage, *wal.WAL) {
 	var walsnap walpb.Snapshot
 	if snapshot != nil {
 		walsnap.Index, walsnap.Term = snapshot.Metadata.Index, snapshot.Metadata.Term
@@ -288,7 +288,7 @@ func restartNode(cfg *ServerConfig, snapshot *raftpb.Snapshot) (types.ID, *clust
 	plog.Infof("restarting member %s in cluster %s at commit index %d", id, cid, st.Commit)
 	cl := newCluster("")
 	cl.SetID(cid)
-	s := raft.NewMemoryStorage()
+	s := newRaftStorage()
 	if snapshot != nil {
 		s.ApplySnapshot(*snapshot)
 	}
@@ -308,7 +308,7 @@ func restartNode(cfg *ServerConfig, snapshot *raftpb.Snapshot) (types.ID, *clust
 	return id, cl, n, s, w
 }
 
-func restartAsStandaloneNode(cfg *ServerConfig, snapshot *raftpb.Snapshot) (types.ID, *cluster, raft.Node, *raft.MemoryStorage, *wal.WAL) {
+func restartAsStandaloneNode(cfg *ServerConfig, snapshot *raftpb.Snapshot) (types.ID, *cluster, raft.Node, *raftStorage, *wal.WAL) {
 	var walsnap walpb.Snapshot
 	if snapshot != nil {
 		walsnap.Index, walsnap.Term = snapshot.Metadata.Index, snapshot.Metadata.Term
@@ -340,7 +340,7 @@ func restartAsStandaloneNode(cfg *ServerConfig, snapshot *raftpb.Snapshot) (type
 	plog.Printf("forcing restart of member %s in cluster %s at commit index %d", id, cid, st.Commit)
 	cl := newCluster("")
 	cl.SetID(cid)
-	s := raft.NewMemoryStorage()
+	s := newRaftStorage()
 	if snapshot != nil {
 		s.ApplySnapshot(*snapshot)
 	}

etcdserver/raft_storage.go

@@ -0,0 +1,47 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package etcdserver
+
+import (
+	"github.com/coreos/etcd/raft"
+	"github.com/coreos/etcd/raft/raftpb"
+)
+
+type raftStorage struct {
+	*raft.MemoryStorage
+	// snapStore is the place to request snapshot when v3demo is enabled.
+	// If snapStore is nil, it uses the snapshot saved in MemoryStorage.
+	snapStore *snapshotStore
+}
+
+func newRaftStorage() *raftStorage {
+	return &raftStorage{
+		MemoryStorage: raft.NewMemoryStorage(),
+	}
+}
+
+// Snapshot returns raft snapshot. If snapStore is nil, this method
+// returns snapshot saved in MemoryStorage. If snapStore exists, this method
+// returns snapshot from snapStore.
+func (rs *raftStorage) Snapshot() (raftpb.Snapshot, error) {
+	if rs.snapStore == nil {
+		return rs.MemoryStorage.Snapshot()
+	}
+	snap, err := rs.snapStore.getSnap()
+	if err != nil {
+		return raftpb.Snapshot{}, err
+	}
+	return snap.raft(), nil
+}

etcdserver/raft_test.go

@@ -153,7 +153,7 @@ func TestStopRaftWhenWaitingForApplyDone(t *testing.T) {
 	r := raftNode{
 		Node:        n,
 		storage:     &storageRecorder{},
-		raftStorage: raft.NewMemoryStorage(),
+		raftStorage: newRaftStorage(),
 		transport:   &nopTransporter{},
 	}
 	r.start(&EtcdServer{r: r})

etcdserver/server.go

@@ -179,7 +179,7 @@ func NewServer(cfg *ServerConfig) (*EtcdServer, error) {
 	st := store.New(StoreClusterPrefix, StoreKeysPrefix)
 	var w *wal.WAL
 	var n raft.Node
-	var s *raft.MemoryStorage
+	var s *raftStorage
 	var id types.ID
 	var cl *cluster
 
@@ -343,6 +343,7 @@ func NewServer(cfg *ServerConfig) (*EtcdServer, error) {
 		if err := srv.kv.Restore(); err != nil {
 			plog.Fatalf("v3 storage restore error: %v", err)
 		}
+		s.snapStore = newSnapshotStore(cfg.StorageDir(), srv.kv)
 	}
 
 	// TODO: move transport initialization near the definition of remote

etcdserver/server_test.go

@@ -522,7 +522,7 @@ func TestDoProposal(t *testing.T) {
 			r: raftNode{
 				Node:        newNodeCommitter(),
 				storage:     &storageRecorder{},
-				raftStorage: raft.NewMemoryStorage(),
+				raftStorage: newRaftStorage(),
 				transport:   &nopTransporter{},
 			},
 			store:    st,
@@ -661,7 +661,7 @@ func TestSyncTrigger(t *testing.T) {
 		cfg: &ServerConfig{TickMs: 1},
 		r: raftNode{
 			Node:        n,
-			raftStorage: raft.NewMemoryStorage(),
+			raftStorage: newRaftStorage(),
 			transport:   &nopTransporter{},
 			storage:     &storageRecorder{},
 		},
@@ -700,7 +700,7 @@ func TestSyncTrigger(t *testing.T) {
 
 // snapshot should snapshot the store and cut the persistent
 func TestSnapshot(t *testing.T) {
-	s := raft.NewMemoryStorage()
+	s := newRaftStorage()
 	s.Append([]raftpb.Entry{{Index: 1}})
 	st := &storeRecorder{}
 	p := &storageRecorder{}
@@ -743,7 +743,7 @@ func TestTriggerSnap(t *testing.T) {
 		snapCount: uint64(snapc),
 		r: raftNode{
 			Node:        newNodeCommitter(),
-			raftStorage: raft.NewMemoryStorage(),
+			raftStorage: newRaftStorage(),
 			storage:     p,
 			transport:   &nopTransporter{},
 		},
@@ -783,7 +783,7 @@ func TestRecvSnapshot(t *testing.T) {
 			Node:        n,
 			transport:   &nopTransporter{},
 			storage:     p,
-			raftStorage: raft.NewMemoryStorage(),
+			raftStorage: newRaftStorage(),
 		},
 		store:   st,
 		cluster: cl,
@@ -812,7 +812,7 @@ func TestApplySnapshotAndCommittedEntries(t *testing.T) {
 	st := &storeRecorder{}
 	cl := newCluster("abc")
 	cl.SetStore(store.New())
-	storage := raft.NewMemoryStorage()
+	storage := newRaftStorage()
 	s := &EtcdServer{
 		r: raftNode{
 			Node:        n,
@@ -860,7 +860,7 @@ func TestAddMember(t *testing.T) {
 	s := &EtcdServer{
 		r: raftNode{
 			Node:        n,
-			raftStorage: raft.NewMemoryStorage(),
+			raftStorage: newRaftStorage(),
 			storage:     &storageRecorder{},
 			transport:   &nopTransporter{},
 		},
@@ -900,7 +900,7 @@ func TestRemoveMember(t *testing.T) {
 	s := &EtcdServer{
 		r: raftNode{
 			Node:        n,
-			raftStorage: raft.NewMemoryStorage(),
+			raftStorage: newRaftStorage(),
 			storage:     &storageRecorder{},
 			transport:   &nopTransporter{},
 		},
@@ -939,7 +939,7 @@ func TestUpdateMember(t *testing.T) {
 	s := &EtcdServer{
 		r: raftNode{
 			Node:        n,
-			raftStorage: raft.NewMemoryStorage(),
+			raftStorage: newRaftStorage(),
 			storage:     &storageRecorder{},
 			transport:   &nopTransporter{},
 		},

etcdserver/snapshot_store.go

@@ -0,0 +1,126 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package etcdserver
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path"
+
+	"github.com/coreos/etcd/pkg/fileutil"
+	"github.com/coreos/etcd/raft"
+	"github.com/coreos/etcd/raft/raftpb"
+	dstorage "github.com/coreos/etcd/storage"
+)
+
+type snapshot struct {
+	r raftpb.Snapshot
+}
+
+func (s *snapshot) raft() raftpb.Snapshot { return s.r }
+
+func (s *snapshot) size() uint64 { return 0 }
+
+func (s *snapshot) writeTo(w io.Writer) (n int64, err error) { return 0, nil }
+
+func (s *snapshot) close() {}
+
+type snapshotStore struct {
+	// dir to save snapshot data
+	dir string
+	kv  dstorage.KV
+
+	// send empty to reqsnapc to notify the channel receiver to send back latest
+	// snapshot to snapc
+	reqsnapc chan struct{}
+	// a chan to receive the requested snapshot
+	// snapshotStore will receive from the chan immediately after it sends empty to reqsnapc
+	snapc chan raftpb.Snapshot
+
+	snap *snapshot
+}
+
+func newSnapshotStore(dir string, kv dstorage.KV) *snapshotStore {
+	return &snapshotStore{
+		dir:      dir,
+		kv:       kv,
+		reqsnapc: make(chan struct{}),
+		snapc:    make(chan raftpb.Snapshot),
+	}
+}
+
+// getSnap returns a snapshot.
+// If there is no available snapshot, ErrSnapshotTemporarilyUnavaliable will be returned.
+func (ss *snapshotStore) getSnap() (*snapshot, error) {
+	if ss.snap != nil {
+		return nil, raft.ErrSnapshotTemporarilyUnavailable
+	}
+
+	// ask to generate v2 snapshot
+	ss.reqsnapc <- struct{}{}
+	// TODO: generate v3 snapshot at here
+	raftsnap := <-ss.snapc
+	ss.snap = &snapshot{
+		r: raftsnap,
+	}
+	return ss.snap, nil
+}
+
+// saveSnap saves snapshot into disk.
+//
+// If snapshot has existed in disk, it keeps the original snapshot and returns error.
+// The function guarantees that it always saves either complete snapshot or no snapshot,
+// even if the call is aborted because program is hard killed.
+func (ss *snapshotStore) saveSnap(s *snapshot) error {
+	f, err := ioutil.TempFile(ss.dir, "tmp")
+	if err != nil {
+		return err
+	}
+	_, err = s.writeTo(f)
+	f.Close()
+	if err != nil {
+		os.Remove(f.Name())
+		return err
+	}
+	fn := path.Join(ss.dir, fmt.Sprintf("%016x.db", s.raft().Metadata.Index))
+	if fileutil.Exist(fn) {
+		os.Remove(f.Name())
+		return fmt.Errorf("snapshot to save has existed")
+	}
+	err = os.Rename(f.Name(), fn)
+	if err != nil {
+		os.Remove(f.Name())
+		return err
+	}
+	return nil
+}
+
+// getSnapFilePath returns the file path for the snapshot with given index.
+// If the snapshot does not exist, it returns error.
+func (ss *snapshotStore) getSnapFilePath(index uint64) (string, error) {
+	fns, err := fileutil.ReadDir(ss.dir)
+	if err != nil {
+		return "", err
+	}
+	wfn := fmt.Sprintf("%016x.db", index)
+	for _, fn := range fns {
+		if fn == wfn {
+			return path.Join(ss.dir, fn), nil
+		}
+	}
+	return "", fmt.Errorf("snapshot file doesn't exist")
+}