etcdserver: Backport snapshot recovery from #7917 to 3.1 branch

etcdserver/backend.go

@@ -0,0 +1,83 @@
+// Copyright 2017 The etcd Authors
+//
+// 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"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/coreos/etcd/lease"
+	"github.com/coreos/etcd/mvcc"
+	"github.com/coreos/etcd/mvcc/backend"
+	"github.com/coreos/etcd/raft/raftpb"
+	"github.com/coreos/etcd/snap"
+)
+
+func newBackend(cfg *ServerConfig) backend.Backend {
+	return backend.NewDefaultBackend(backendPath(cfg))
+}
+
+func backendPath(cfg *ServerConfig) string {
+	return filepath.Join(cfg.SnapDir(), "db")
+}
+
+// openSnapshotBackend renames a snapshot db to the current etcd db and opens it.
+func openSnapshotBackend(cfg *ServerConfig, ss *snap.Snapshotter, snapshot raftpb.Snapshot) (backend.Backend, error) {
+	snapPath, err := ss.DBFilePath(snapshot.Metadata.Index)
+	if err != nil {
+		return nil, fmt.Errorf("failed to find database snapshot file (%v)", err)
+	}
+	if err := os.Rename(snapPath, backendPath(cfg)); err != nil {
+		return nil, fmt.Errorf("failed to rename database snapshot file (%v)", err)
+	}
+	return openBackend(cfg), nil
+}
+
+// openBackend returns a backend using the current etcd db.
+func openBackend(cfg *ServerConfig) backend.Backend {
+	fn := backendPath(cfg)
+	beOpened := make(chan backend.Backend)
+	go func() {
+		beOpened <- newBackend(cfg)
+	}()
+
+	select {
+	case be := <-beOpened:
+		return be
+
+	case <-time.After(10 * time.Second):
+		plog.Warningf("another etcd process is using %q and holds the file lock, or loading backend file is taking >10 seconds", fn)
+		plog.Warningf("waiting for it to exit before starting...")
+	}
+
+	return <-beOpened
+}
+
+// recoverBackendSnapshot recovers the DB from a snapshot in case etcd crashes
+// before updating the backend db after persisting raft snapshot to disk,
+// violating the invariant snapshot.Metadata.Index < db.consistentIndex. In this
+// case, replace the db with the snapshot db sent by the leader.
+func recoverSnapshotBackend(cfg *ServerConfig, oldbe backend.Backend, snapshot raftpb.Snapshot) (backend.Backend, error) {
+	var cIndex consistentIndex
+	kv := mvcc.New(oldbe, &lease.FakeLessor{}, &cIndex)
+	defer kv.Close()
+	if snapshot.Metadata.Index <= kv.ConsistentIndex() {
+		return oldbe, nil
+	}
+	oldbe.Close()
+	return openSnapshotBackend(cfg, snap.New(cfg.SnapDir()), snapshot)
+}

etcdserver/server.go

@@ -378,6 +378,10 @@ func NewServer(cfg *ServerConfig) (srv *EtcdServer, err error) {
 				plog.Panicf("recovered store from snapshot error: %v", err)
 			}
 			plog.Infof("recovered store from snapshot at index %d", snapshot.Metadata.Index)
+
+			if be, err = recoverSnapshotBackend(cfg, be, *snapshot); err != nil {
+				plog.Panicf("recovering backend from snapshot error: %v", err)
+			}
 		}
 		cfg.Print()
 		if !cfg.ForceNewCluster {