node.go

// Copyright 2017-2021 Lei Ni (nilei81@gmail.com) and other contributors.
//
// 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 dragonboat

import (
	"sync"
	"sync/atomic"

	"github.com/cockroachdb/errors"
	"github.com/lni/goutils/logutil"

	"github.com/lni/dragonboat/v4/client"
	"github.com/lni/dragonboat/v4/config"
	"github.com/lni/dragonboat/v4/internal/fileutil"
	"github.com/lni/dragonboat/v4/internal/logdb"
	"github.com/lni/dragonboat/v4/internal/raft"
	"github.com/lni/dragonboat/v4/internal/rsm"
	"github.com/lni/dragonboat/v4/internal/server"
	"github.com/lni/dragonboat/v4/internal/settings"
	"github.com/lni/dragonboat/v4/internal/transport"
	"github.com/lni/dragonboat/v4/raftio"
	pb "github.com/lni/dragonboat/v4/raftpb"
	sm "github.com/lni/dragonboat/v4/statemachine"
)

var (
	incomingProposalsMaxLen = settings.Soft.IncomingProposalQueueLength
	incomingReadIndexMaxLen = settings.Soft.IncomingReadIndexQueueLength
	syncTaskInterval        = settings.Soft.SyncTaskInterval
	lazyFreeCycle           = settings.Soft.LazyFreeCycle
)

type pipeline interface {
	setCloseReady(*node)
	setStepReady(shardID uint64)
	setCommitReady(shardID uint64)
	setApplyReady(shardID uint64)
	setStreamReady(shardID uint64)
	setSaveReady(shardID uint64)
	setRecoverReady(shardID uint64)
}

type logDBMetrics struct {
	busy int32
}

func (l *logDBMetrics) update(busy bool) {
	v := int32(0)
	if busy {
		v = int32(1)
	}
	atomic.StoreInt32(&l.busy, v)
}

func (l *logDBMetrics) isBusy() bool {
	return atomic.LoadInt32(&l.busy) != 0
}

type leaderInfo struct {
	leaderID uint64
	term     uint64
}

type node struct {
	shardInfo             atomic.Value
	leaderInfo            atomic.Value
	nodeRegistry          raftio.INodeRegistry
	logdb                 raftio.ILogDB
	pipeline              pipeline
	getStreamSink         func(uint64, uint64) *transport.Sink
	ss                    snapshotState
	configChangeC         <-chan configChangeRequest
	snapshotC             <-chan rsm.SSRequest
	toApplyQ              *rsm.TaskQueue
	toCommitQ             *rsm.TaskQueue
	syncTask              task
	metrics               *logDBMetrics
	stopC                 chan struct{}
	sysEvents             *sysEventListener
	raftEvents            *raftEventListener
	handleSnapshotStatus  func(uint64, uint64, bool)
	sendRaftMessage       func(pb.Message)
	validateTarget        func(string) bool
	sm                    *rsm.StateMachine
	incomingReadIndexes   *readIndexQueue
	incomingProposals     *entryQueue
	snapshotLock          sync.Mutex
	pendingProposals      pendingProposal
	pendingReadIndexes    pendingReadIndex
	pendingConfigChange   pendingConfigChange
	pendingSnapshot       pendingSnapshot
	pendingLeaderTransfer pendingLeaderTransfer
	pendingRaftLogQuery   pendingRaftLogQuery
	initializedC          chan struct{}
	p                     raft.Peer
	logReader             *logdb.LogReader
	snapshotter           *snapshotter
	mq                    *server.MessageQueue
	qs                    *quiesceState
	raftAddress           string
	config                config.Config
	currentTick           uint64
	gcTick                uint64
	appliedIndex          uint64
	pushedIndex           uint64
	confirmedIndex        uint64
	tickMillisecond       uint64
	shardID               uint64
	replicaID             uint64
	instanceID            uint64
	initializedFlag       uint64
	closeOnce             sync.Once
	raftMu                sync.Mutex
	new                   bool
	logDBLimited          bool
	rateLimited           bool
	notifyCommit          bool
}

var _ rsm.INode = (*node)(nil)

var instanceID uint64

func newNode(peers map[uint64]string,
	initialMember bool,
	config config.Config,
	nhConfig config.NodeHostConfig,
	createSM rsm.ManagedStateMachineFactory,
	snapshotter *snapshotter,
	logReader *logdb.LogReader,
	pipeline pipeline,
	liQueue *leaderInfoQueue,
	getStreamSink func(uint64, uint64) *transport.Sink,
	handleSnapshotStatus func(uint64, uint64, bool),
	sendMessage func(pb.Message),
	nodeRegistry raftio.INodeRegistry,
	pool *sync.Pool,
	ldb raftio.ILogDB,
	metrics *logDBMetrics,
	sysEvents *sysEventListener) (*node, error) {
	notifyCommit := nhConfig.NotifyCommit
	proposals := newEntryQueue(incomingProposalsMaxLen, lazyFreeCycle)
	readIndexes := newReadIndexQueue(incomingReadIndexMaxLen)
	configChangeC := make(chan configChangeRequest, 1)
	snapshotC := make(chan rsm.SSRequest, 1)
	stopC := make(chan struct{})
	mq := server.NewMessageQueue(receiveQueueLen,
		false, lazyFreeCycle, nhConfig.MaxReceiveQueueSize)
	rn := &node{
		shardID:               config.ShardID,
		replicaID:             config.ReplicaID,
		raftAddress:           nhConfig.RaftAddress,
		instanceID:            atomic.AddUint64(&instanceID, 1),
		tickMillisecond:       nhConfig.RTTMillisecond,
		config:                config,
		incomingProposals:     proposals,
		incomingReadIndexes:   readIndexes,
		configChangeC:         configChangeC,
		snapshotC:             snapshotC,
		pipeline:              pipeline,
		getStreamSink:         getStreamSink,
		handleSnapshotStatus:  handleSnapshotStatus,
		stopC:                 stopC,
		pendingProposals:      newPendingProposal(config, notifyCommit, pool, proposals),
		pendingReadIndexes:    newPendingReadIndex(pool, readIndexes),
		pendingConfigChange:   newPendingConfigChange(configChangeC, notifyCommit),
		pendingSnapshot:       newPendingSnapshot(snapshotC),
		pendingLeaderTransfer: newPendingLeaderTransfer(),
		pendingRaftLogQuery:   newPendingRaftLogQuery(),
		nodeRegistry:          nodeRegistry,
		snapshotter:           snapshotter,
		logReader:             logReader,
		sendRaftMessage:       sendMessage,
		mq:                    mq,
		logdb:                 ldb,
		syncTask:              newTask(syncTaskInterval),
		sysEvents:             sysEvents,
		notifyCommit:          notifyCommit,
		metrics:               metrics,
		initializedC:          make(chan struct{}),
		ss:                    snapshotState{},
		validateTarget:        nhConfig.GetTargetValidator(),
		qs: &quiesceState{
			electionTick: config.ElectionRTT * 2,
			enabled:      config.Quiesce,
			shardID:      config.ShardID,
			replicaID:    config.ReplicaID,
		},
	}
	ds := createSM(config.ShardID, config.ReplicaID, stopC)
	sm := rsm.NewStateMachine(ds, snapshotter, config, rn, snapshotter.fs)
	if notifyCommit {
		rn.toCommitQ = rsm.NewTaskQueue()
	}
	rn.toApplyQ = sm.TaskQ()
	rn.sm = sm
	rn.raftEvents = newRaftEventListener(config.ShardID,
		config.ReplicaID, nhConfig.EnableMetrics, liQueue)
	new, err := rn.startRaft(config, peers, initialMember)
	if err != nil {
		return nil, err
	}
	rn.new = new
	return rn, nil
}

func (n *node) ReplicaID() uint64 {
	return n.replicaID
}

func (n *node) ShardID() uint64 {
	return n.shardID
}

func (n *node) ShouldStop() <-chan struct{} {
	return n.stopC
}

func (n *node) StepReady() {
	n.pipeline.setStepReady(n.shardID)
}

func (n *node) applyReady() {
	n.pipeline.setApplyReady(n.shardID)
}

func (n *node) commitReady() {
	n.pipeline.setCommitReady(n.shardID)
}

func (n *node) ApplyUpdate(e pb.Entry,
	result sm.Result, rejected bool, ignored bool, notifyRead bool) {
	if n.isWitness() {
		return
	}
	if notifyRead {
		n.pendingReadIndexes.applied(e.Index)
	}
	if !ignored {
		if e.Key == 0 {
			plog.Panicf("key is 0")
		}
		n.pendingProposals.applied(e.ClientID, e.SeriesID, e.Key, result, rejected)
	}
}

func (n *node) ApplyConfigChange(cc pb.ConfigChange,
	key uint64, rejected bool) error {
	n.raftMu.Lock()
	defer n.raftMu.Unlock()
	if !rejected {
		if err := n.applyConfigChange(cc); err != nil {
			return err
		}
	}
	return n.configChangeProcessed(key, rejected)
}

func (n *node) applyConfigChange(cc pb.ConfigChange) error {
	if err := n.p.ApplyConfigChange(cc); err != nil {
		return err
	}
	switch cc.Type {
	case pb.AddNode, pb.AddNonVoting, pb.AddWitness:
		n.nodeRegistry.Add(n.shardID, cc.ReplicaID, cc.Address)
	case pb.RemoveNode:
		if cc.ReplicaID == n.replicaID {
			plog.Infof("%s applied ConfChange Remove for itself", n.id())
			n.nodeRegistry.RemoveShard(n.shardID)
			n.requestRemoval()
			n.notifySelfRemove()
		} else {
			n.nodeRegistry.Remove(n.shardID, cc.ReplicaID)
		}
	default:
		plog.Panicf("unknown config change type, %s", cc.Type)
	}
	return nil
}

func (n *node) configChangeProcessed(key uint64, rejected bool) error {
	if n.isWitness() {
		return nil
	}
	if rejected {
		if err := n.p.RejectConfigChange(); err != nil {
			return err
		}
	} else {
		n.notifyConfigChange()
	}
	n.pendingConfigChange.apply(key, rejected)
	return nil
}

func (n *node) processLeaderUpdate(u pb.LeaderUpdate) {
	if u.Term == 0 {
		return
	}
	leaderInfo := &leaderInfo{
		leaderID: u.LeaderID,
		term:     u.Term,
	}
	n.leaderInfo.Store(leaderInfo)
}

func (n *node) processLogQuery(r pb.LogQueryResult) {
	if r.IsEmpty() {
		return
	}
	outOfRange := false
	if r.Error != nil {
		if errors.Is(r.Error, raft.ErrCompacted) {
			outOfRange = true
		} else {
			panic(r.Error)
		}
	}
	n.pendingRaftLogQuery.returned(outOfRange,
		LogRange{FirstIndex: r.FirstIndex, LastIndex: r.LastIndex}, r.Entries)
}

func (n *node) RestoreRemotes(snapshot pb.Snapshot) error {
	if snapshot.Membership.ConfigChangeId == 0 {
		plog.Panicf("invalid ConfChangeId")
	}
	n.raftMu.Lock()
	defer n.raftMu.Unlock()
	for nid, addr := range snapshot.Membership.Addresses {
		n.nodeRegistry.Add(n.shardID, nid, addr)
	}
	for nid, addr := range snapshot.Membership.NonVotings {
		n.nodeRegistry.Add(n.shardID, nid, addr)
	}
	for nid, addr := range snapshot.Membership.Witnesses {
		n.nodeRegistry.Add(n.shardID, nid, addr)
	}
	for nid := range snapshot.Membership.Removed {
		if nid == n.replicaID {
			n.nodeRegistry.RemoveShard(n.shardID)
			n.requestRemoval()
			n.notifySelfRemove()
		}
	}
	plog.Debugf("%s is restoring remotes", n.id())
	if err := n.p.RestoreRemotes(snapshot); err != nil {
		return err
	}
	n.notifyConfigChange()
	return nil
}

func (n *node) startRaft(cfg config.Config,
	peers map[uint64]string, initial bool) (bool, error) {
	newNode, err := n.replayLog(cfg.ShardID, cfg.ReplicaID)
	if err != nil {
		return false, err
	}
	pas := make([]raft.PeerAddress, 0)
	for k, v := range peers {
		pas = append(pas, raft.PeerAddress{ReplicaID: k, Address: v})
	}
	n.p = raft.Launch(cfg, n.logReader, n.raftEvents, pas, initial, newNode)
	return newNode, nil
}

func (n *node) close() {
	n.requestRemoval()
	n.raftEvents.close()
	n.mq.Close()
	n.pendingReadIndexes.close()
	n.pendingProposals.close()
	n.pendingConfigChange.close()
	n.pendingSnapshot.close()
	n.pendingRaftLogQuery.close()
}

func (n *node) stopped() bool {
	select {
	case <-n.stopC:
		return true
	default:
	}
	return false
}

func (n *node) requestRemoval() {
	n.closeOnce.Do(func() {
		close(n.stopC)
	})
	plog.Debugf("%s called requestRemoval()", n.id())
}

func (n *node) concurrentSnapshot() bool {
	return n.sm.Concurrent()
}

func (n *node) supportClientSession() bool {
	return !n.OnDiskStateMachine() && !n.isWitness()
}

func (n *node) isWitness() bool {
	return n.config.IsWitness
}

func (n *node) OnDiskStateMachine() bool {
	return n.sm.OnDiskStateMachine()
}

func (n *node) proposeSession(session *client.Session,
	timeout uint64) (*RequestState, error) {
	if !n.initialized() {
		return nil, ErrShardNotReady
	}
	if n.isWitness() {
		return nil, ErrInvalidOperation
	}
	if !session.ValidForSessionOp(n.shardID) {
		return nil, ErrInvalidSession
	}
	return n.pendingProposals.propose(session, nil, timeout)
}

func (n *node) payloadTooBig(sz int) bool {
	if n.config.MaxInMemLogSize == 0 {
		return false
	}
	return uint64(sz+settings.EntryNonCmdFieldsSize) > n.config.MaxInMemLogSize
}

func (n *node) propose(session *client.Session,
	cmd []byte, timeout uint64) (*RequestState, error) {
	if !n.initialized() {
		return nil, ErrShardNotReady
	}
	if n.isWitness() {
		return nil, ErrInvalidOperation
	}
	if !session.ValidForProposal(n.shardID) {
		return nil, ErrInvalidSession
	}
	if n.payloadTooBig(len(cmd)) {
		return nil, ErrPayloadTooBig
	}
	return n.pendingProposals.propose(session, cmd, timeout)
}

func (n *node) read(timeout uint64) (*RequestState, error) {
	if !n.initialized() {
		return nil, ErrShardNotReady
	}
	if n.isWitness() {
		return nil, ErrInvalidOperation
	}
	rs, err := n.pendingReadIndexes.read(timeout)
	if err == nil {
		rs.node = n
	}
	return rs, err
}

func (n *node) requestLeaderTransfer(replicaID uint64) error {
	if !n.initialized() {
		return ErrShardNotReady
	}
	if n.isWitness() {
		return ErrInvalidOperation
	}
	return n.pendingLeaderTransfer.request(replicaID)
}

func (n *node) requestSnapshot(opt SnapshotOption,
	timeout uint64) (*RequestState, error) {
	if !n.initialized() {
		return nil, ErrShardNotReady
	}
	if n.isWitness() {
		return nil, ErrInvalidOperation
	}
	st := rsm.UserRequested
	if opt.Exported {
		plog.Debugf("%s called export snapshot", n.id())
		st = rsm.Exported
		exist, err := fileutil.Exist(opt.ExportPath, n.snapshotter.fs)
		if err != nil {
			return nil, err
		}
		if !exist {
			return nil, ErrDirNotExist
		}
	} else {
		if len(opt.ExportPath) > 0 {
			plog.Warningf("opt.ExportPath set when not exporting a snapshot")
			opt.ExportPath = ""
		}
	}
	return n.pendingSnapshot.request(st,
		opt.ExportPath,
		opt.OverrideCompactionOverhead,
		opt.CompactionOverhead,
		opt.CompactionIndex,
		timeout)
}

func (n *node) queryRaftLog(firstIndex uint64,
	lastIndex uint64, maxSize uint64) (*RequestState, error) {
	if !n.initialized() {
		return nil, ErrShardNotReady
	}
	if n.isWitness() {
		return nil, ErrInvalidOperation
	}
	return n.pendingRaftLogQuery.add(firstIndex, lastIndex, maxSize)
}

func (n *node) reportIgnoredSnapshotRequest(key uint64) {
	n.pendingSnapshot.apply(key, true, false, 0)
}

func (n *node) requestConfigChange(cct pb.ConfigChangeType,
	replicaID uint64, target string, orderID uint64,
	timeout uint64) (*RequestState, error) {
	if !n.initialized() {
		return nil, ErrShardNotReady
	}
	if n.isWitness() {
		return nil, ErrInvalidOperation
	}
	if cct != pb.RemoveNode && !n.validateTarget(target) {
		return nil, ErrInvalidAddress
	}
	cc := pb.ConfigChange{
		Type:           cct,
		ReplicaID:      replicaID,
		ConfigChangeId: orderID,
		Address:        target,
	}
	return n.pendingConfigChange.request(cc, timeout)
}

func (n *node) requestDeleteNodeWithOrderID(replicaID uint64,
	order uint64, timeout uint64) (*RequestState, error) {
	return n.requestConfigChange(pb.RemoveNode, replicaID, "", order, timeout)
}

func (n *node) requestAddNodeWithOrderID(replicaID uint64,
	target string, order uint64, timeout uint64) (*RequestState, error) {
	return n.requestConfigChange(pb.AddNode, replicaID, target, order, timeout)
}

func (n *node) requestAddNonVotingWithOrderID(replicaID uint64,
	target string, order uint64, timeout uint64) (*RequestState, error) {
	return n.requestConfigChange(pb.AddNonVoting, replicaID, target, order, timeout)
}

func (n *node) requestAddWitnessWithOrderID(replicaID uint64,
	target string, order uint64, timeout uint64) (*RequestState, error) {
	return n.requestConfigChange(pb.AddWitness, replicaID, target, order, timeout)
}

func (n *node) getLeaderID() (uint64, uint64, bool) {
	lv := n.leaderInfo.Load()
	if lv == nil {
		return 0, 0, false
	}
	leaderInfo := lv.(*leaderInfo)
	return leaderInfo.leaderID, leaderInfo.term, leaderInfo.leaderID != raft.NoLeader
}

func (n *node) destroy() error {
	return n.sm.Close()
}

func (n *node) destroyed() bool {
	select {
	case <-n.sm.DestroyedC():
		return true
	default:
	}

	return false
}

func (n *node) offloaded() {
	if n.sm.Offloaded() {
		n.pipeline.setCloseReady(n)
		n.sysEvents.Publish(server.SystemEvent{
			Type:      server.NodeUnloaded,
			ShardID:   n.shardID,
			ReplicaID: n.replicaID,
		})
	}
}

func (n *node) loaded() {
	n.sm.Loaded()
}

func (n *node) pushTask(rec rsm.Task, notify bool) {
	if n.notifyCommit {
		n.toCommitQ.Add(rec)
		if notify {
			n.commitReady()
		}
	} else {
		n.toApplyQ.Add(rec)
		if notify {
			n.applyReady()
		}
	}
}

func (n *node) pushEntries(ents []pb.Entry) {
	if len(ents) == 0 {
		return
	}
	n.pushTask(rsm.Task{Entries: ents}, false)
	n.pushedIndex = ents[len(ents)-1].Index
}

func (n *node) pushStreamSnapshotRequest(shardID uint64, replicaID uint64) {
	n.pushTask(rsm.Task{
		ShardID:   shardID,
		ReplicaID: replicaID,
		Stream:    true,
	}, true)
}

func (n *node) pushTakeSnapshotRequest(req rsm.SSRequest) {
	n.pushTask(rsm.Task{
		Save:      true,
		SSRequest: req,
	}, true)
}

func (n *node) pushSnapshot(ss pb.Snapshot, applied uint64) {
	if pb.IsEmptySnapshot(ss) {
		return
	}
	if ss.Index < n.pushedIndex ||
		ss.Index < n.ss.getIndex() ||
		ss.Index < applied {
		plog.Panicf("out of date snapshot, index %d, pushed %d, applied %d, ss %d",
			ss.Index, n.pushedIndex, applied, n.ss.getIndex())
	}
	n.pushTask(rsm.Task{
		Recover: true,
		Index:   ss.Index,
	}, true)
	n.ss.setIndex(ss.Index)
	n.pushedIndex = ss.Index
}

func (n *node) replayLog(shardID uint64, replicaID uint64) (bool, error) {
	plog.Infof("%s replaying raft logs", n.id())
	ss, err := n.snapshotter.GetSnapshotFromLogDB()
	if err != nil && !n.snapshotter.IsNoSnapshotError(err) {
		return false, errors.Wrapf(err, "%s failed to get latest snapshot", n.id())
	}
	if !pb.IsEmptySnapshot(ss) {
		if err = n.logReader.ApplySnapshot(ss); err != nil {
			return false, errors.Wrapf(err, "%s failed to apply snapshot", n.id())
		}
	}
	rs, err := n.logdb.ReadRaftState(shardID, replicaID, ss.Index)
	if errors.Is(err, raftio.ErrNoSavedLog) {
		return true, nil
	}
	if err != nil {
		return false, errors.Wrapf(err, "%s ReadRaftState failed", n.id())
	}
	hasRaftState := !pb.IsEmptyState(rs.State)
	if hasRaftState {
		plog.Infof("%s logdb first entry %d size %d commit %d term %d",
			n.id(), rs.FirstIndex, rs.EntryCount, rs.State.Commit, rs.State.Term)
		n.logReader.SetState(rs.State)
	}
	n.logReader.SetRange(rs.FirstIndex, rs.EntryCount)
	return !(ss.Index > 0 || rs.EntryCount > 0 || hasRaftState), nil
}

func (n *node) saveSnapshotRequired(applied uint64) bool {
	if n.config.SnapshotEntries == 0 {
		return false
	}
	index := n.ss.getIndex()
	if n.pushedIndex <= n.config.SnapshotEntries+index ||
		applied <= n.config.SnapshotEntries+index ||
		applied <= n.config.SnapshotEntries+n.ss.getReqIndex() {
		return false
	}
	if n.isBusySnapshotting() {
		return false
	}
	plog.Debugf("%s requested to create %s", n.id(), n.ssid(applied))
	n.ss.setReqIndex(applied)
	return true
}

func isSoftSnapshotError(err error) bool {
	return errors.Is(err, raft.ErrCompacted) ||
		errors.Is(err, raft.ErrSnapshotOutOfDate)
}

func saveAborted(err error) bool {
	return errors.Is(err, sm.ErrSnapshotStopped) ||
		errors.Is(err, sm.ErrSnapshotAborted)
}

func snapshotCommitAborted(err error) bool {
	return errors.Is(err, errSnapshotOutOfDate)
}

func streamAborted(err error) bool {
	return saveAborted(err) || errors.Is(err, sm.ErrSnapshotStreaming)
}

func openAborted(err error) bool {
	return errors.Is(err, sm.ErrOpenStopped)
}

func recoverAborted(err error) bool {
	return errors.Is(err, sm.ErrSnapshotStopped) ||
		errors.Is(err, raft.ErrSnapshotOutOfDate)
}

func (n *node) save(rec rsm.Task) error {
	index, err := n.doSave(rec.SSRequest)
	if err != nil {
		return err
	}
	n.pendingSnapshot.apply(rec.SSRequest.Key, index == 0, false, index)
	n.sysEvents.Publish(server.SystemEvent{
		Type:      server.SnapshotCreated,
		ShardID:   n.shardID,
		ReplicaID: n.replicaID,
	})
	return nil
}

func (n *node) doSave(req rsm.SSRequest) (uint64, error) {
	n.snapshotLock.Lock()
	defer n.snapshotLock.Unlock()
	if !req.Exported() && n.sm.GetLastApplied() <= n.ss.getIndex() {
		// a snapshot has been pushed to the sm but not applied yet
		// or the snapshot has been applied and there is no further progress
		return 0, nil
	}
	ss, ssenv, err := n.sm.Save(req)
	if err != nil {
		if saveAborted(err) {
			plog.Warningf("%s save snapshot aborted, %v", n.id(), err)
			ssenv.MustRemoveTempDir()
			n.pendingSnapshot.apply(req.Key, false, true, 0)
			return 0, nil
		} else if isSoftSnapshotError(err) {
			// e.g. trying to save a snapshot at the same index twice
			return 0, nil
		}
		return 0, errors.Wrapf(err, "%s save snapshot failed", n.id())
	}
	plog.Infof("%s saved %s, term %d, file count %d",
		n.id(), n.ssid(ss.Index), ss.Term, len(ss.Files))
	if err := n.snapshotter.Commit(ss, req); err != nil {
		if snapshotCommitAborted(err) || saveAborted(err) {
			// saveAborted() will only be true in monkey test
			// commit abort happens when the final dir already exists, probably due to
			// incoming snapshot
			ssenv.MustRemoveTempDir()
			return 0, nil
		}
		return 0, errors.Wrapf(err, "%s commit snapshot failed", n.id())
	}
	if req.Exported() {
		return ss.Index, nil
	}
	if !ss.Validate(n.snapshotter.fs) {
		plog.Panicf("%s generated invalid snapshot %v", n.id(), ss)
	}
	if err = n.logReader.CreateSnapshot(ss); err != nil {
		if isSoftSnapshotError(err) {
			return 0, nil
		}
		return 0, errors.Wrapf(err, "%s create snapshot failed", n.id())
	}
	n.compactLog(req, ss.Index)
	n.ss.setIndex(ss.Index)
	return ss.Index, nil
}

func (n *node) compactLog(req rsm.SSRequest, index uint64) {
	if compactionIndex, ok := n.getCompactionIndex(req, index); ok {
		n.ss.setCompactLogTo(compactionIndex)
	}
}

func (n *node) getCompactionIndex(req rsm.SSRequest, index uint64) (uint64, bool) {
	if req.OverrideCompaction {
		if req.CompactionIndex > 0 {
			if index >= req.CompactionIndex+1 {
				return req.CompactionIndex, true
			}
			return 0, false
		}
		if index > req.CompactionOverhead {
			return index - req.CompactionOverhead, true
		}
		return 0, false
	}
	if index > n.config.CompactionOverhead {
		return index - n.config.CompactionOverhead, true
	}

	return 0, false
}

func (n *node) stream(sink pb.IChunkSink) error {
	if sink != nil {
		plog.Infof("%s requested to stream to %d", n.id(), sink.ToReplicaID())
		if err := n.sm.Stream(sink); err != nil {
			if !streamAborted(err) {
				return errors.Wrapf(err, "%s stream failed", n.id())
			}
		}
	}
	return nil
}

func (n *node) recover(rec rsm.Task) (_ uint64, err error) {
	n.snapshotLock.Lock()
	defer n.snapshotLock.Unlock()
	if rec.Initial && n.OnDiskStateMachine() {
		plog.Debugf("%s on disk SM is beng initialized", n.id())
		idx, err := n.sm.OpenOnDiskStateMachine()
		if err != nil {
			if openAborted(err) {
				plog.Warningf("%s aborted OpenOnDiskStateMachine", n.id())
				return 0, nil
			}
			return 0, errors.Wrapf(err, "%s OpenOnDiskStateMachine failed", n.id())
		}
		if idx > 0 && rec.NewNode {
			plog.Panicf("%s new node at non-zero index %d", n.id(), idx)
		}
	}
	ss, err := n.sm.Recover(rec)
	if err != nil {
		if recoverAborted(err) {
			plog.Warningf("%s aborted recovery", n.id())
			return 0, nil
		}
		return 0, errors.Wrapf(err, "%s recover failed", n.id())
	}
	if !pb.IsEmptySnapshot(ss) {
		defer func() {
			err = firstError(err, ss.Unref())
		}()
		plog.Infof("%s recovered from %s", n.id(), n.ssid(ss.Index))
		if n.OnDiskStateMachine() {
			if err := n.sm.Sync(); err != nil {
				return 0, errors.Wrapf(err, "%s sync failed", n.id())
			}
			if err := n.snapshotter.Shrink(ss.Index); err != nil {
				return 0, errors.Wrapf(err, "%s shrink failed", n.id())
			}
		}
		n.compactLog(rsm.DefaultSSRequest, ss.Index)
	}
	n.sysEvents.Publish(server.SystemEvent{
		Type:      server.SnapshotRecovered,
		ShardID:   n.shardID,
		ReplicaID: n.replicaID,
		Index:     ss.Index,
	})
	return ss.Index, nil
}

func (n *node) streamDone() {
	n.ss.notifySnapshotStatus(false, false, true, false, 0)
	n.applyReady()
}

func (n *node) saveDone() {
	n.ss.notifySnapshotStatus(true, false, false, false, 0)
	n.applyReady()
}

func (n *node) recoverDone(index uint64) {
	if !n.initialized() {
		n.initialSnapshotDone(index)
	} else {
		n.recoverFromSnapshotDone()
	}
}

func (n *node) initialSnapshotDone(index uint64) {
	n.ss.notifySnapshotStatus(false, true, false, true, index)
	n.applyReady()
}

func (n *node) recoverFromSnapshotDone() {
	n.ss.notifySnapshotStatus(false, true, false, false, 0)
	n.applyReady()
}

func (n *node) handleTask(ts []rsm.Task, es []sm.Entry) (rsm.Task, error) {
	return n.sm.Handle(ts, es)
}

func (n *node) removeSnapshotFlagFile(index uint64) error {
	return n.snapshotter.removeFlagFile(index)
}

func (n *node) runSyncTask() {
	if !n.sm.OnDiskStateMachine() {
		return
	}
	if !n.syncTask.timeToRun(n.millisecondSinceStart()) {
		return
	}
	if !n.sm.TaskChanBusy() {
		n.pushTask(rsm.Task{PeriodicSync: true}, true)
	}
}

func (n *node) removeLog() error {
	if n.ss.hasCompactLogTo() {
		compactTo := n.ss.getCompactLogTo()
		if compactTo == 0 {
			panic("racy compact log to value?")
		}
		if err := n.logReader.Compact(compactTo); err != nil {
			if err != raft.ErrCompacted {
				return err
			}
		}
		if err := n.logdb.RemoveEntriesTo(n.shardID,
			n.replicaID, compactTo); err != nil {
			return err
		}
		plog.Infof("%s compacted log up to index %d", n.id(), compactTo)
		n.ss.setCompactedTo(compactTo)
		n.sysEvents.Publish(server.SystemEvent{
			Type:      server.LogCompacted,
			ShardID:   n.shardID,
			ReplicaID: n.replicaID,
			Index:     compactTo,
		})
		if !n.config.DisableAutoCompactions {
			if _, err := n.requestCompaction(); err != nil {
				if err != ErrRejected {
					return errors.Wrapf(err, "%s failed to request compaction", n.id())
				}
			}
		}
	}
	return nil
}

func (n *node) requestCompaction() (*SysOpState, error) {
	if compactTo := n.ss.getCompactedTo(); compactTo > 0 {
		done, err := n.logdb.CompactEntriesTo(n.shardID, n.replicaID, compactTo)
		if err != nil {
			return nil, err
		}
		n.sysEvents.Publish(server.SystemEvent{
			Type:      server.LogDBCompacted,
			ShardID:   n.shardID,
			ReplicaID: n.replicaID,
			Index:     compactTo,
		})
		return &SysOpState{completedC: done}, nil
	}
	return nil, ErrRejected
}

func isFreeOrderMessage(m pb.Message) bool {
	return m.Type == pb.Replicate || m.Type == pb.Ping
}

func (n *node) sendEnterQuiesceMessages() {
	for replicaID := range n.sm.GetMembership().Addresses {
		if replicaID != n.replicaID {
			msg := pb.Message{
				Type:    pb.Quiesce,
				From:    n.replicaID,
				To:      replicaID,
				ShardID: n.shardID,
			}
			n.sendRaftMessage(msg)
		}
	}
}

func (n *node) sendMessages(msgs []pb.Message) {
	for _, msg := range msgs {
		if !isFreeOrderMessage(msg) {
			msg.ShardID = n.shardID
			n.sendRaftMessage(msg)
		}
	}
}

func (n *node) sendReplicateMessages(ud pb.Update) {
	for _, msg := range ud.Messages {
		if isFreeOrderMessage(msg) {
			msg.ShardID = n.shardID
			n.sendRaftMessage(msg)
		}
	}
}

func (n *node) getUpdate() (pb.Update, bool, error) {
	moreEntries := n.moreEntriesToApply()
	if n.p.HasUpdate(moreEntries) ||
		n.confirmedIndex != n.appliedIndex ||
		n.ss.hasCompactLogTo() || n.ss.hasCompactedTo() {
		if n.appliedIndex < n.confirmedIndex {
			plog.Panicf("applied index moving backwards, %d, now %d",
				n.confirmedIndex, n.appliedIndex)
		}
		ud, err := n.p.GetUpdate(moreEntries, n.appliedIndex)
		if err != nil {
			return pb.Update{}, false, err
		}
		n.confirmedIndex = n.appliedIndex
		return ud, true, nil
	}
	return pb.Update{}, false, nil
}

func (n *node) processDroppedReadIndexes(ud pb.Update) {
	for _, sysctx := range ud.DroppedReadIndexes {
		n.pendingReadIndexes.dropped(sysctx)
	}
}

func (n *node) processDroppedEntries(ud pb.Update) {
	for _, e := range ud.DroppedEntries {
		if e.IsProposal() {
			n.pendingProposals.dropped(e.ClientID, e.SeriesID, e.Key)
		} else if e.Type == pb.ConfigChangeEntry {
			n.pendingConfigChange.dropped(e.Key)
		} else {
			plog.Panicf("unknown entry type %s", e.Type)
		}
	}
}

func (n *node) notifyCommittedEntries() {
	tasks := n.toCommitQ.GetAll()
	for _, t := range tasks {
		for _, e := range t.Entries {
			if e.IsProposal() {
				n.pendingProposals.committed(e.ClientID, e.SeriesID, e.Key)
			} else if e.Type == pb.ConfigChangeEntry {
				n.pendingConfigChange.committed(e.Key)
			} else {
				plog.Panicf("unknown entry type %s", e.Type)
			}
		}
		n.toApplyQ.Add(t)
	}
	if len(tasks) > 0 {
		n.applyReady()
	}
}

func (n *node) processReadyToRead(ud pb.Update) {
	if len(ud.ReadyToReads) > 0 {
		n.pendingReadIndexes.addReady(ud.ReadyToReads)
		n.pendingReadIndexes.applied(ud.LastApplied)
	}
}

func (n *node) processSnapshot(ud pb.Update) error {
	if !pb.IsEmptySnapshot(ud.Snapshot) {
		err := n.logReader.ApplySnapshot(ud.Snapshot)
		if err != nil && !isSoftSnapshotError(err) {
			return errors.Wrapf(err, "%s failed to apply snapshot", n.id())
		}
		plog.Debugf("%s, push snapshot %d", n.id(), ud.Snapshot.Index)
		n.pushSnapshot(ud.Snapshot, ud.LastApplied)
	}
	return nil
}

func (n *node) applyRaftUpdates(ud pb.Update) {
	n.pushEntries(pb.EntriesToApply(ud.CommittedEntries, n.pushedIndex, true))
}

func (n *node) processRaftUpdate(ud pb.Update) error {
	if err := n.logReader.Append(ud.EntriesToSave); err != nil {
		return err
	}
	n.sendMessages(ud.Messages)
	if err := n.removeLog(); err != nil {
		return err
	}
	n.runSyncTask()
	if n.saveSnapshotRequired(ud.LastApplied) {
		n.pushTakeSnapshotRequest(rsm.SSRequest{})
	}
	return nil
}

func (n *node) commitRaftUpdate(ud pb.Update) {
	n.raftMu.Lock()
	n.p.Commit(ud)
	n.raftMu.Unlock()
}

func (n *node) moreEntriesToApply() bool {
	return n.toApplyQ.MoreEntryToApply()
}

func (n *node) hasEntryToApply() bool {
	return n.p.HasEntryToApply()
}

func (n *node) updateAppliedIndex() uint64 {
	n.appliedIndex = n.sm.GetLastApplied()
	n.p.NotifyRaftLastApplied(n.appliedIndex)
	return n.appliedIndex
}

func (n *node) stepNode() (pb.Update, bool, error) {
	n.raftMu.Lock()
	defer n.raftMu.Unlock()
	if n.initialized() {
		hasEvent, err := n.handleEvents()
		if err != nil {
			return pb.Update{}, false, err
		}
		if hasEvent {
			if n.qs.newQuiesceState() {
				n.sendEnterQuiesceMessages()
			}
			ud, hasUpdate, err := n.getUpdate()
			if err != nil {
				return pb.Update{}, false, err
			}
			return ud, hasUpdate, nil
		}
	}
	return pb.Update{}, false, nil
}

func (n *node) handleEvents() (bool, error) {
	hasEvent := false
	lastApplied := n.updateAppliedIndex()
	if lastApplied != n.confirmedIndex {
		hasEvent = true
	}
	if n.hasEntryToApply() {
		hasEvent = true
	}
	event, err := n.handleReadIndex()
	if err != nil {
		return false, err
	}
	if event {
		hasEvent = true
	}
	event, err = n.handleReceivedMessages()
	if err != nil {
		return false, err
	}
	if event {
		hasEvent = true
	}
	event, err = n.handleConfigChange()
	if err != nil {
		return false, err
	}
	if event {
		hasEvent = true
	}
	event, err = n.handleProposals()
	if err != nil {
		return false, err
	}
	if event {
		hasEvent = true
	}
	event, err = n.handleLeaderTransfer()
	if err != nil {
		return false, err
	}
	if event {
		hasEvent = true
	}
	if n.handleSnapshot(lastApplied) {
		hasEvent = true
	}
	if n.handleCompaction() {
		hasEvent = true
	}
	event, err = n.handleLogQuery()
	if err != nil {
		return false, err
	}
	if event {
		hasEvent = true
	}
	n.gc()
	if hasEvent {
		n.pendingReadIndexes.applied(lastApplied)
	}
	return hasEvent, nil
}

func (n *node) gc() {
	if n.gcTick != n.currentTick {
		n.pendingProposals.gc()
		n.pendingConfigChange.gc()
		n.pendingSnapshot.gc()
		n.gcTick = n.currentTick
	}
}

func (n *node) handleCompaction() bool {
	return n.ss.hasCompactedTo() || n.ss.hasCompactLogTo()
}

func (n *node) handleLogQuery() (bool, error) {
	if req := n.pendingRaftLogQuery.get(); req != nil {
		if err := n.p.QueryRaftLog(req.logRange.FirstIndex,
			req.logRange.LastIndex, req.maxSize); err != nil {
			return false, err
		}
		return true, nil
	}
	return false, nil
}

func (n *node) handleLeaderTransfer() (bool, error) {
	target, ok := n.pendingLeaderTransfer.get()
	if ok {
		if err := n.p.RequestLeaderTransfer(target); err != nil {
			return false, err
		}
	}
	return ok, nil
}

func (n *node) handleSnapshot(lastApplied uint64) bool {
	var req rsm.SSRequest
	select {
	case req = <-n.snapshotC:
	default:
		return false
	}
	if !req.Exported() && lastApplied == n.ss.getReqIndex() {
		n.reportIgnoredSnapshotRequest(req.Key)
		return false
	}
	n.ss.setReqIndex(lastApplied)
	n.pushTakeSnapshotRequest(req)
	return true
}

func (n *node) handleProposals() (bool, error) {
	rateLimited := n.p.RateLimited()
	if n.rateLimited != rateLimited {
		n.rateLimited = rateLimited
		plog.Infof("%s new rate limit state is %t", n.id(), rateLimited)
	}
	logDBBusy := n.logDBBusy()
	if n.logDBLimited != logDBBusy {
		n.logDBLimited = logDBBusy
		plog.Infof("%s new LogDB busy state is %t", n.id(), logDBBusy)
	}
	paused := logDBBusy || n.rateLimited
	if entries := n.incomingProposals.get(paused); len(entries) > 0 {
		if err := n.p.ProposeEntries(entries); err != nil {
			return false, err
		}
		return true, nil
	}
	return false, nil
}

func (n *node) handleReadIndex() (bool, error) {
	if reqs := n.incomingReadIndexes.get(); len(reqs) > 0 {
		n.qs.record(pb.ReadIndex)
		ctx := n.pendingReadIndexes.nextCtx()
		n.pendingReadIndexes.add(ctx, reqs)
		if err := n.p.ReadIndex(ctx); err != nil {
			return false, err
		}
		return true, nil
	}
	return false, nil
}

func (n *node) handleConfigChange() (bool, error) {
	if len(n.configChangeC) == 0 {
		return false, nil
	}
	select {
	case req, ok := <-n.configChangeC:
		if !ok {
			n.configChangeC = nil
		} else {
			n.qs.record(pb.ConfigChangeEvent)
			var cc pb.ConfigChange
			pb.MustUnmarshal(&cc, req.data)
			if err := n.p.ProposeConfigChange(cc, req.key); err != nil {
				return false, err
			}
		}
	default:
		return false, nil
	}
	return true, nil
}

func (n *node) isBusySnapshotting() bool {
	snapshotting := n.ss.recovering()
	if !n.concurrentSnapshot() {
		snapshotting = snapshotting || n.ss.saving()
	}
	return snapshotting && n.sm.TaskChanBusy()
}

func (n *node) recordMessage(m pb.Message) {
	if (m.Type == pb.Heartbeat || m.Type == pb.HeartbeatResp) && m.Hint > 0 {
		n.qs.record(pb.ReadIndex)
	} else {
		n.qs.record(m.Type)
	}
}

func (n *node) handleReceivedMessages() (bool, error) {
	count := uint64(0)
	busy := n.isBusySnapshotting()
	msgs := n.mq.Get()
	for _, m := range msgs {
		if m.Type == pb.LocalTick {
			count++
		} else if m.Type == pb.Replicate && busy {
			continue
		}
		done, err := n.handleMessage(m)
		if err != nil {
			return false, err
		}
		if !done {
			n.recordMessage(m)
			if err := n.p.Handle(m); err != nil {
				return false, err
			}
		}
	}
	if count > n.config.ElectionRTT/2 {
		plog.Warningf("%s had %d LocalTick msgs in one batch", n.id(), count)
	}
	if lazyFreeCycle > 0 {
		for i := range msgs {
			msgs[i].Entries = nil
		}
	}
	return len(msgs) > 0, nil
}

func (n *node) handleMessage(m pb.Message) (bool, error) {
	switch m.Type {
	case pb.LocalTick:
		if err := n.tick(m.Hint); err != nil {
			return false, err
		}
	case pb.Quiesce:
		n.qs.tryEnterQuiesce()
	case pb.SnapshotStatus:
		plog.Debugf("%s got ReportSnapshot from %d, rejected %t",
			n.id(), m.From, m.Reject)
		if err := n.p.ReportSnapshotStatus(m.From, m.Reject); err != nil {
			return false, err
		}
	case pb.Unreachable:
		if err := n.p.ReportUnreachableNode(m.From); err != nil {
			return false, err
		}
	default:
		return false, nil
	}
	return true, nil
}

func (n *node) setInitialStatus(index uint64) {
	if n.initialized() {
		plog.Panicf("setInitialStatus called twice")
	}
	plog.Infof("%s initial index set to %d", n.id(), index)
	n.ss.setIndex(index)
	n.pushedIndex = index
	n.setInitialized()
}

func (n *node) handleSnapshotTask(task rsm.Task) {
	if n.ss.recovering() {
		plog.Panicf("%s recovering from snapshot again on %s",
			n.id(), n.getRaftAddress())
	}
	if task.Recover {
		n.reportRecoverSnapshot(task)
	} else if task.Save {
		if n.ss.saving() {
			plog.Warningf("%s taking snapshot, ignored new snapshot req", n.id())
			n.reportIgnoredSnapshotRequest(task.SSRequest.Key)
			return
		}
		n.reportSaveSnapshot(task)
	} else if task.Stream {
		if !n.canStream() {
			n.reportSnapshotStatus(task.ShardID, task.ReplicaID, true)
			return
		}
		n.reportStreamSnapshot(task)
	} else {
		plog.Panicf("unknown task type %+v", task)
	}
}

func (n *node) reportSnapshotStatus(shardID uint64,
	replicaID uint64, failed bool) {
	n.handleSnapshotStatus(shardID, replicaID, failed)
}

func (n *node) reportStreamSnapshot(rec rsm.Task) {
	n.ss.setStreaming()
	getSinkFn := func() pb.IChunkSink {
		conn := n.getStreamSink(rec.ShardID, rec.ReplicaID)
		if conn == nil {
			plog.Errorf("failed to connect to %s", dn(rec.ShardID, rec.ReplicaID))
			return nil
		}
		return conn
	}
	n.ss.setStreamReq(rec, getSinkFn)
	n.pipeline.setStreamReady(n.shardID)
}

func (n *node) canStream() bool {
	if n.ss.streaming() {
		plog.Warningf("%s ignored task.StreamSnapshot", n.id())
		return false
	}
	if !n.sm.ReadyToStream() {
		plog.Warningf("%s is not ready to stream snapshot", n.id())
		return false
	}
	return true
}

func (n *node) reportSaveSnapshot(rec rsm.Task) {
	n.ss.setSaving()
	n.ss.setSaveReq(rec)
	n.pipeline.setSaveReady(n.shardID)
}

func (n *node) reportRecoverSnapshot(rec rsm.Task) {
	n.ss.setRecovering()
	n.ss.setRecoverReq(rec)
	n.pipeline.setRecoverReady(n.shardID)
}

// returns a boolean flag indicating whether to skip task handling for the
// current node
func (n *node) processStatusTransition() bool {
	if n.processSaveStatus() {
		return true
	}
	if n.processStreamStatus() {
		return true
	}
	if n.processRecoverStatus() {
		return true
	}
	if n.processUninitializedNodeStatus() {
		return true
	}
	return false
}

func (n *node) processUninitializedNodeStatus() bool {
	if !n.initialized() {
		plog.Debugf("%s checking initial snapshot", n.id())
		n.reportRecoverSnapshot(rsm.Task{
			Recover: true,
			Initial: true,
			NewNode: n.new,
		})
		return true
	}
	return false
}

func (n *node) processRecoverStatus() bool {
	if n.ss.recovering() {
		rec, ok := n.ss.getRecoverCompleted()
		if !ok {
			return true
		}
		if rec.Save {
			plog.Panicf("got a completed.SnapshotRequested")
		}
		if rec.Initial {
			plog.Infof("%s initialized using %s", n.id(), n.ssid(rec.Index))
			n.setInitialStatus(rec.Index)
			n.sysEvents.Publish(server.SystemEvent{
				Type:      server.NodeReady,
				ShardID:   n.shardID,
				ReplicaID: n.replicaID,
			})
		}
		n.ss.clearRecovering()
	}
	return false
}

func (n *node) processSaveStatus() bool {
	if n.ss.saving() {
		rec, ok := n.ss.getSaveCompleted()
		if !ok {
			return !n.concurrentSnapshot()
		}
		if rec.Save && !n.initialized() {
			plog.Panicf("%s taking snapshot when uninitialized", n.id())
		}
		n.ss.clearSaving()
	}
	return false
}

func (n *node) processStreamStatus() bool {
	if n.ss.streaming() {
		if !n.OnDiskStateMachine() {
			plog.Panicf("non-on disk sm is streaming snapshot")
		}
		if _, ok := n.ss.getStreamCompleted(); !ok {
			return false
		}
		n.ss.clearStreaming()
	}
	return false
}

func (n *node) tick(tick uint64) error {
	n.currentTick++
	n.qs.tick()
	if n.qs.quiesced() {
		if err := n.p.QuiescedTick(); err != nil {
			return err
		}
	} else {
		if err := n.p.Tick(); err != nil {
			return err
		}
	}
	n.pendingSnapshot.tick(tick)
	n.pendingProposals.tick(tick)
	n.pendingReadIndexes.tick(tick)
	n.pendingConfigChange.tick(tick)
	return nil
}

func (n *node) notifySelfRemove() {
	n.sysEvents.Publish(server.SystemEvent{
		Type:      server.NodeDeleted,
		ShardID:   n.shardID,
		ReplicaID: n.replicaID,
	})
}

func (n *node) notifyConfigChange() {
	m := n.sm.GetMembership()
	if len(m.Addresses) == 0 {
		plog.Panicf("empty nodes %s", n.id())
	}
	_, isNonVoting := m.NonVotings[n.replicaID]
	_, isWitness := m.Witnesses[n.replicaID]
	ci := &ShardInfo{
		ShardID:           n.shardID,
		ReplicaID:         n.replicaID,
		IsNonVoting:       isNonVoting,
		IsWitness:         isWitness,
		ConfigChangeIndex: m.ConfigChangeId,
		Replicas:          m.Addresses,
	}
	n.shardInfo.Store(ci)
	n.sysEvents.Publish(server.SystemEvent{
		Type:      server.MembershipChanged,
		ShardID:   n.shardID,
		ReplicaID: n.replicaID,
	})
}

func (n *node) getShardInfo() ShardInfo {
	v := n.shardInfo.Load()
	if v == nil {
		return ShardInfo{
			ShardID:          n.shardID,
			ReplicaID:        n.replicaID,
			Pending:          true,
			StateMachineType: sm.Type(n.sm.Type()),
		}
	}
	info := v.(*ShardInfo)

	leaderID := uint64(0)
	term := uint64(0)
	lv := n.leaderInfo.Load()
	if lv != nil {
		leaderInfo := lv.(*leaderInfo)
		leaderID = leaderInfo.leaderID
		term = leaderInfo.term
	}

	return ShardInfo{
		ShardID:           info.ShardID,
		ReplicaID:         info.ReplicaID,
		LeaderID:          leaderID,
		Term:              term,
		IsNonVoting:       info.IsNonVoting,
		ConfigChangeIndex: info.ConfigChangeIndex,
		Replicas:          info.Replicas,
		StateMachineType:  sm.Type(n.sm.Type()),
	}
}

func (n *node) logDBBusy() bool {
	if n.metrics == nil {
		// only happens in tests
		return false
	}
	return n.metrics.isBusy()
}

func (n *node) id() string {
	return dn(n.shardID, n.replicaID)
}

func (n *node) ssid(index uint64) string {
	return logutil.DescribeSS(n.shardID, n.replicaID, index)
}

func (n *node) isLeader() bool {
	v := n.leaderInfo.Load()
	if v == nil {
		return false
	}
	leaderInfo := v.(*leaderInfo)
	if leaderInfo.term == 0 {
		return false
	}
	return n.replicaID == leaderInfo.leaderID
}

func (n *node) isFollower() bool {
	v := n.leaderInfo.Load()
	if v == nil {
		return false
	}
	leaderInfo := v.(*leaderInfo)
	if leaderInfo.term == 0 {
		return false
	}
	return n.replicaID != leaderInfo.leaderID
}

func (n *node) initialized() bool {
	if atomic.LoadUint64(&n.initializedFlag) != 0 {
		return true
	}
	select {
	case <-n.initializedC:
		atomic.StoreUint64(&n.initializedFlag, 1)
		return true
	default:
	}
	return false
}

func (n *node) setInitialized() {
	close(n.initializedC)
}

func (n *node) millisecondSinceStart() uint64 {
	return n.tickMillisecond * n.currentTick
}

func (n *node) getRaftAddress() string {
	return n.raftAddress
}