etcdserver/snapshot_merge.go
func (s *EtcdServer) createMergedSnapshotMessage(m raftpb.Message, snapt, snapi uint64, confState raftpb.ConfState) snap.Message {
	// get a snapshot of v2 store as []byte
	clone := s.v2store.Clone()
	d, err := clone.SaveNoCopy()
	if err != nil {
		if lg := s.getLogger(); lg != nil {
			lg.Panic("failed to save v2 store data", zap.Error(err))
		} else {
			plog.Panicf("store save should never fail: %v", err)
		}
	}

	// commit kv to write metadata(for example: consistent index).
	s.KV().Commit()
	dbsnap := s.be.Snapshot()
	// get a snapshot of v3 KV as readCloser
	rc := newSnapshotReaderCloser(s.getLogger(), dbsnap)

	// put the []byte snapshot of store into raft snapshot and return the merged snapshot with
	// KV readCloser snapshot.
	snapshot := raftpb.Snapshot{
		Metadata: raftpb.SnapshotMetadata{
			Index:     snapi,
			Term:      snapt,
			ConfState: confState,
		},
		Data: d,
	}
	m.Snapshot = snapshot

	return *snap.NewMessage(m, rc, dbsnap.Size())
}
func (s *EtcdServer) createMergedSnapshotMessage(m raftpb.Message, snapt, snapi uint64, confState raftpb.ConfState) snap.Message {
	// get a snapshot of v2 store as []byte
	clone := s.v2store.Clone()
	d, err := clone.SaveNoCopy()
	if err != nil {
		if lg := s.getLogger(); lg != nil {
			lg.Panic("failed to save v2 store data", zap.Error(err))
		} else {
			plog.Panicf("store save should never fail: %v", err)
		}
	}

	// commit kv to write metadata(for example: consistent index).
	s.KV().Commit()
	dbsnap := s.be.Snapshot()
	// get a snapshot of v3 KV as readCloser
	rc := newSnapshotReaderCloser(s.getLogger(), dbsnap)

	// put the []byte snapshot of store into raft snapshot and return the merged snapshot with
	// KV readCloser snapshot.
	snapshot := raftpb.Snapshot{
		Metadata: raftpb.SnapshotMetadata{
			Index:     snapi,
			Term:      snapt,
			ConfState: confState,
		},
		Data: d,
	}
	m.Snapshot = snapshot

	return *snap.NewMessage(m, rc, dbsnap.Size())
}
// createMergedSnapshotMessage creates a snapshot message that contains: raft status (term, conf),
// a snapshot of v2 store inside raft.Snapshot as []byte, a snapshot of v3 KV in the top level message
// as ReadCloser.