https://github.com/etcd-io/etcd
Tip revision: e694b7bb087538c146e188a29753967d189d202b authored by Gyuho Lee on 01 April 2020, 17:46:54 UTC
version: 3.4.7
version: 3.4.7
Tip revision: e694b7b
raft.go
// Copyright 2015 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 raft
import (
"bytes"
"errors"
"fmt"
"math"
"math/rand"
"sort"
"strings"
"sync"
"time"
"go.etcd.io/etcd/raft/confchange"
"go.etcd.io/etcd/raft/quorum"
pb "go.etcd.io/etcd/raft/raftpb"
"go.etcd.io/etcd/raft/tracker"
)
// None is a placeholder node ID used when there is no leader.
const None uint64 = 0
const noLimit = math.MaxUint64
// Possible values for StateType.
const (
StateFollower StateType = iota
StateCandidate
StateLeader
StatePreCandidate
numStates
)
type ReadOnlyOption int
const (
// ReadOnlySafe guarantees the linearizability of the read only request by
// communicating with the quorum. It is the default and suggested option.
ReadOnlySafe ReadOnlyOption = iota
// ReadOnlyLeaseBased ensures linearizability of the read only request by
// relying on the leader lease. It can be affected by clock drift.
// If the clock drift is unbounded, leader might keep the lease longer than it
// should (clock can move backward/pause without any bound). ReadIndex is not safe
// in that case.
ReadOnlyLeaseBased
)
// Possible values for CampaignType
const (
// campaignPreElection represents the first phase of a normal election when
// Config.PreVote is true.
campaignPreElection CampaignType = "CampaignPreElection"
// campaignElection represents a normal (time-based) election (the second phase
// of the election when Config.PreVote is true).
campaignElection CampaignType = "CampaignElection"
// campaignTransfer represents the type of leader transfer
campaignTransfer CampaignType = "CampaignTransfer"
)
// ErrProposalDropped is returned when the proposal is ignored by some cases,
// so that the proposer can be notified and fail fast.
var ErrProposalDropped = errors.New("raft proposal dropped")
// lockedRand is a small wrapper around rand.Rand to provide
// synchronization among multiple raft groups. Only the methods needed
// by the code are exposed (e.g. Intn).
type lockedRand struct {
mu sync.Mutex
rand *rand.Rand
}
func (r *lockedRand) Intn(n int) int {
r.mu.Lock()
v := r.rand.Intn(n)
r.mu.Unlock()
return v
}
var globalRand = &lockedRand{
rand: rand.New(rand.NewSource(time.Now().UnixNano())),
}
// CampaignType represents the type of campaigning
// the reason we use the type of string instead of uint64
// is because it's simpler to compare and fill in raft entries
type CampaignType string
// StateType represents the role of a node in a cluster.
type StateType uint64
var stmap = [...]string{
"StateFollower",
"StateCandidate",
"StateLeader",
"StatePreCandidate",
}
func (st StateType) String() string {
return stmap[uint64(st)]
}
// Config contains the parameters to start a raft.
type Config struct {
// ID is the identity of the local raft. ID cannot be 0.
ID uint64
// peers contains the IDs of all nodes (including self) in the raft cluster. It
// should only be set when starting a new raft cluster. Restarting raft from
// previous configuration will panic if peers is set. peer is private and only
// used for testing right now.
peers []uint64
// learners contains the IDs of all learner nodes (including self if the
// local node is a learner) in the raft cluster. learners only receives
// entries from the leader node. It does not vote or promote itself.
learners []uint64
// ElectionTick is the number of Node.Tick invocations that must pass between
// elections. That is, if a follower does not receive any message from the
// leader of current term before ElectionTick has elapsed, it will become
// candidate and start an election. ElectionTick must be greater than
// HeartbeatTick. We suggest ElectionTick = 10 * HeartbeatTick to avoid
// unnecessary leader switching.
ElectionTick int
// HeartbeatTick is the number of Node.Tick invocations that must pass between
// heartbeats. That is, a leader sends heartbeat messages to maintain its
// leadership every HeartbeatTick ticks.
HeartbeatTick int
// Storage is the storage for raft. raft generates entries and states to be
// stored in storage. raft reads the persisted entries and states out of
// Storage when it needs. raft reads out the previous state and configuration
// out of storage when restarting.
Storage Storage
// Applied is the last applied index. It should only be set when restarting
// raft. raft will not return entries to the application smaller or equal to
// Applied. If Applied is unset when restarting, raft might return previous
// applied entries. This is a very application dependent configuration.
Applied uint64
// MaxSizePerMsg limits the max byte size of each append message. Smaller
// value lowers the raft recovery cost(initial probing and message lost
// during normal operation). On the other side, it might affect the
// throughput during normal replication. Note: math.MaxUint64 for unlimited,
// 0 for at most one entry per message.
MaxSizePerMsg uint64
// MaxCommittedSizePerReady limits the size of the committed entries which
// can be applied.
MaxCommittedSizePerReady uint64
// MaxUncommittedEntriesSize limits the aggregate byte size of the
// uncommitted entries that may be appended to a leader's log. Once this
// limit is exceeded, proposals will begin to return ErrProposalDropped
// errors. Note: 0 for no limit.
MaxUncommittedEntriesSize uint64
// MaxInflightMsgs limits the max number of in-flight append messages during
// optimistic replication phase. The application transportation layer usually
// has its own sending buffer over TCP/UDP. Setting MaxInflightMsgs to avoid
// overflowing that sending buffer. TODO (xiangli): feedback to application to
// limit the proposal rate?
MaxInflightMsgs int
// CheckQuorum specifies if the leader should check quorum activity. Leader
// steps down when quorum is not active for an electionTimeout.
CheckQuorum bool
// PreVote enables the Pre-Vote algorithm described in raft thesis section
// 9.6. This prevents disruption when a node that has been partitioned away
// rejoins the cluster.
PreVote bool
// ReadOnlyOption specifies how the read only request is processed.
//
// ReadOnlySafe guarantees the linearizability of the read only request by
// communicating with the quorum. It is the default and suggested option.
//
// ReadOnlyLeaseBased ensures linearizability of the read only request by
// relying on the leader lease. It can be affected by clock drift.
// If the clock drift is unbounded, leader might keep the lease longer than it
// should (clock can move backward/pause without any bound). ReadIndex is not safe
// in that case.
// CheckQuorum MUST be enabled if ReadOnlyOption is ReadOnlyLeaseBased.
ReadOnlyOption ReadOnlyOption
// Logger is the logger used for raft log. For multinode which can host
// multiple raft group, each raft group can have its own logger
Logger Logger
// DisableProposalForwarding set to true means that followers will drop
// proposals, rather than forwarding them to the leader. One use case for
// this feature would be in a situation where the Raft leader is used to
// compute the data of a proposal, for example, adding a timestamp from a
// hybrid logical clock to data in a monotonically increasing way. Forwarding
// should be disabled to prevent a follower with an inaccurate hybrid
// logical clock from assigning the timestamp and then forwarding the data
// to the leader.
DisableProposalForwarding bool
}
func (c *Config) validate() error {
if c.ID == None {
return errors.New("cannot use none as id")
}
if c.HeartbeatTick <= 0 {
return errors.New("heartbeat tick must be greater than 0")
}
if c.ElectionTick <= c.HeartbeatTick {
return errors.New("election tick must be greater than heartbeat tick")
}
if c.Storage == nil {
return errors.New("storage cannot be nil")
}
if c.MaxUncommittedEntriesSize == 0 {
c.MaxUncommittedEntriesSize = noLimit
}
// default MaxCommittedSizePerReady to MaxSizePerMsg because they were
// previously the same parameter.
if c.MaxCommittedSizePerReady == 0 {
c.MaxCommittedSizePerReady = c.MaxSizePerMsg
}
if c.MaxInflightMsgs <= 0 {
return errors.New("max inflight messages must be greater than 0")
}
if c.Logger == nil {
c.Logger = raftLogger
}
if c.ReadOnlyOption == ReadOnlyLeaseBased && !c.CheckQuorum {
return errors.New("CheckQuorum must be enabled when ReadOnlyOption is ReadOnlyLeaseBased")
}
return nil
}
type raft struct {
id uint64
Term uint64
Vote uint64
readStates []ReadState
// the log
raftLog *raftLog
maxMsgSize uint64
maxUncommittedSize uint64
// TODO(tbg): rename to trk.
prs tracker.ProgressTracker
state StateType
// isLearner is true if the local raft node is a learner.
isLearner bool
msgs []pb.Message
// the leader id
lead uint64
// leadTransferee is id of the leader transfer target when its value is not zero.
// Follow the procedure defined in raft thesis 3.10.
leadTransferee uint64
// Only one conf change may be pending (in the log, but not yet
// applied) at a time. This is enforced via pendingConfIndex, which
// is set to a value >= the log index of the latest pending
// configuration change (if any). Config changes are only allowed to
// be proposed if the leader's applied index is greater than this
// value.
pendingConfIndex uint64
// an estimate of the size of the uncommitted tail of the Raft log. Used to
// prevent unbounded log growth. Only maintained by the leader. Reset on
// term changes.
uncommittedSize uint64
readOnly *readOnly
// number of ticks since it reached last electionTimeout when it is leader
// or candidate.
// number of ticks since it reached last electionTimeout or received a
// valid message from current leader when it is a follower.
electionElapsed int
// number of ticks since it reached last heartbeatTimeout.
// only leader keeps heartbeatElapsed.
heartbeatElapsed int
checkQuorum bool
preVote bool
heartbeatTimeout int
electionTimeout int
// randomizedElectionTimeout is a random number between
// [electiontimeout, 2 * electiontimeout - 1]. It gets reset
// when raft changes its state to follower or candidate.
randomizedElectionTimeout int
disableProposalForwarding bool
tick func()
step stepFunc
logger Logger
}
func newRaft(c *Config) *raft {
if err := c.validate(); err != nil {
panic(err.Error())
}
raftlog := newLogWithSize(c.Storage, c.Logger, c.MaxCommittedSizePerReady)
hs, cs, err := c.Storage.InitialState()
if err != nil {
panic(err) // TODO(bdarnell)
}
if len(c.peers) > 0 || len(c.learners) > 0 {
if len(cs.Voters) > 0 || len(cs.Learners) > 0 {
// TODO(bdarnell): the peers argument is always nil except in
// tests; the argument should be removed and these tests should be
// updated to specify their nodes through a snapshot.
panic("cannot specify both newRaft(peers, learners) and ConfState.(Voters, Learners)")
}
cs.Voters = c.peers
cs.Learners = c.learners
}
r := &raft{
id: c.ID,
lead: None,
isLearner: false,
raftLog: raftlog,
maxMsgSize: c.MaxSizePerMsg,
maxUncommittedSize: c.MaxUncommittedEntriesSize,
prs: tracker.MakeProgressTracker(c.MaxInflightMsgs),
electionTimeout: c.ElectionTick,
heartbeatTimeout: c.HeartbeatTick,
logger: c.Logger,
checkQuorum: c.CheckQuorum,
preVote: c.PreVote,
readOnly: newReadOnly(c.ReadOnlyOption),
disableProposalForwarding: c.DisableProposalForwarding,
}
cfg, prs, err := confchange.Restore(confchange.Changer{
Tracker: r.prs,
LastIndex: raftlog.lastIndex(),
}, cs)
if err != nil {
panic(err)
}
assertConfStatesEquivalent(r.logger, cs, r.switchToConfig(cfg, prs))
if !IsEmptyHardState(hs) {
r.loadState(hs)
}
if c.Applied > 0 {
raftlog.appliedTo(c.Applied)
}
r.becomeFollower(r.Term, None)
var nodesStrs []string
for _, n := range r.prs.VoterNodes() {
nodesStrs = append(nodesStrs, fmt.Sprintf("%x", n))
}
r.logger.Infof("newRaft %x [peers: [%s], term: %d, commit: %d, applied: %d, lastindex: %d, lastterm: %d]",
r.id, strings.Join(nodesStrs, ","), r.Term, r.raftLog.committed, r.raftLog.applied, r.raftLog.lastIndex(), r.raftLog.lastTerm())
return r
}
func (r *raft) hasLeader() bool { return r.lead != None }
func (r *raft) softState() *SoftState { return &SoftState{Lead: r.lead, RaftState: r.state} }
func (r *raft) hardState() pb.HardState {
return pb.HardState{
Term: r.Term,
Vote: r.Vote,
Commit: r.raftLog.committed,
}
}
// send persists state to stable storage and then sends to its mailbox.
func (r *raft) send(m pb.Message) {
m.From = r.id
if m.Type == pb.MsgVote || m.Type == pb.MsgVoteResp || m.Type == pb.MsgPreVote || m.Type == pb.MsgPreVoteResp {
if m.Term == 0 {
// All {pre-,}campaign messages need to have the term set when
// sending.
// - MsgVote: m.Term is the term the node is campaigning for,
// non-zero as we increment the term when campaigning.
// - MsgVoteResp: m.Term is the new r.Term if the MsgVote was
// granted, non-zero for the same reason MsgVote is
// - MsgPreVote: m.Term is the term the node will campaign,
// non-zero as we use m.Term to indicate the next term we'll be
// campaigning for
// - MsgPreVoteResp: m.Term is the term received in the original
// MsgPreVote if the pre-vote was granted, non-zero for the
// same reasons MsgPreVote is
panic(fmt.Sprintf("term should be set when sending %s", m.Type))
}
} else {
if m.Term != 0 {
panic(fmt.Sprintf("term should not be set when sending %s (was %d)", m.Type, m.Term))
}
// do not attach term to MsgProp, MsgReadIndex
// proposals are a way to forward to the leader and
// should be treated as local message.
// MsgReadIndex is also forwarded to leader.
if m.Type != pb.MsgProp && m.Type != pb.MsgReadIndex {
m.Term = r.Term
}
}
r.msgs = append(r.msgs, m)
}
// sendAppend sends an append RPC with new entries (if any) and the
// current commit index to the given peer.
func (r *raft) sendAppend(to uint64) {
r.maybeSendAppend(to, true)
}
// maybeSendAppend sends an append RPC with new entries to the given peer,
// if necessary. Returns true if a message was sent. The sendIfEmpty
// argument controls whether messages with no entries will be sent
// ("empty" messages are useful to convey updated Commit indexes, but
// are undesirable when we're sending multiple messages in a batch).
func (r *raft) maybeSendAppend(to uint64, sendIfEmpty bool) bool {
pr := r.prs.Progress[to]
if pr.IsPaused() {
return false
}
m := pb.Message{}
m.To = to
term, errt := r.raftLog.term(pr.Next - 1)
ents, erre := r.raftLog.entries(pr.Next, r.maxMsgSize)
if len(ents) == 0 && !sendIfEmpty {
return false
}
if errt != nil || erre != nil { // send snapshot if we failed to get term or entries
if !pr.RecentActive {
r.logger.Debugf("ignore sending snapshot to %x since it is not recently active", to)
return false
}
m.Type = pb.MsgSnap
snapshot, err := r.raftLog.snapshot()
if err != nil {
if err == ErrSnapshotTemporarilyUnavailable {
r.logger.Debugf("%x failed to send snapshot to %x because snapshot is temporarily unavailable", r.id, to)
return false
}
panic(err) // TODO(bdarnell)
}
if IsEmptySnap(snapshot) {
panic("need non-empty snapshot")
}
m.Snapshot = snapshot
sindex, sterm := snapshot.Metadata.Index, snapshot.Metadata.Term
r.logger.Debugf("%x [firstindex: %d, commit: %d] sent snapshot[index: %d, term: %d] to %x [%s]",
r.id, r.raftLog.firstIndex(), r.raftLog.committed, sindex, sterm, to, pr)
pr.BecomeSnapshot(sindex)
r.logger.Debugf("%x paused sending replication messages to %x [%s]", r.id, to, pr)
} else {
m.Type = pb.MsgApp
m.Index = pr.Next - 1
m.LogTerm = term
m.Entries = ents
m.Commit = r.raftLog.committed
if n := len(m.Entries); n != 0 {
switch pr.State {
// optimistically increase the next when in StateReplicate
case tracker.StateReplicate:
last := m.Entries[n-1].Index
pr.OptimisticUpdate(last)
pr.Inflights.Add(last)
case tracker.StateProbe:
pr.ProbeSent = true
default:
r.logger.Panicf("%x is sending append in unhandled state %s", r.id, pr.State)
}
}
}
r.send(m)
return true
}
// sendHeartbeat sends a heartbeat RPC to the given peer.
func (r *raft) sendHeartbeat(to uint64, ctx []byte) {
// Attach the commit as min(to.matched, r.committed).
// When the leader sends out heartbeat message,
// the receiver(follower) might not be matched with the leader
// or it might not have all the committed entries.
// The leader MUST NOT forward the follower's commit to
// an unmatched index.
commit := min(r.prs.Progress[to].Match, r.raftLog.committed)
m := pb.Message{
To: to,
Type: pb.MsgHeartbeat,
Commit: commit,
Context: ctx,
}
r.send(m)
}
// bcastAppend sends RPC, with entries to all peers that are not up-to-date
// according to the progress recorded in r.prs.
func (r *raft) bcastAppend() {
r.prs.Visit(func(id uint64, _ *tracker.Progress) {
if id == r.id {
return
}
r.sendAppend(id)
})
}
// bcastHeartbeat sends RPC, without entries to all the peers.
func (r *raft) bcastHeartbeat() {
lastCtx := r.readOnly.lastPendingRequestCtx()
if len(lastCtx) == 0 {
r.bcastHeartbeatWithCtx(nil)
} else {
r.bcastHeartbeatWithCtx([]byte(lastCtx))
}
}
func (r *raft) bcastHeartbeatWithCtx(ctx []byte) {
r.prs.Visit(func(id uint64, _ *tracker.Progress) {
if id == r.id {
return
}
r.sendHeartbeat(id, ctx)
})
}
func (r *raft) advance(rd Ready) {
// If entries were applied (or a snapshot), update our cursor for
// the next Ready. Note that if the current HardState contains a
// new Commit index, this does not mean that we're also applying
// all of the new entries due to commit pagination by size.
if index := rd.appliedCursor(); index > 0 {
r.raftLog.appliedTo(index)
if r.prs.Config.AutoLeave && index >= r.pendingConfIndex && r.state == StateLeader {
// If the current (and most recent, at least for this leader's term)
// configuration should be auto-left, initiate that now.
ccdata, err := (&pb.ConfChangeV2{}).Marshal()
if err != nil {
panic(err)
}
ent := pb.Entry{
Type: pb.EntryConfChangeV2,
Data: ccdata,
}
if !r.appendEntry(ent) {
// If we could not append the entry, bump the pending conf index
// so that we'll try again later.
//
// TODO(tbg): test this case.
r.pendingConfIndex = r.raftLog.lastIndex()
} else {
r.logger.Infof("initiating automatic transition out of joint configuration %s", r.prs.Config)
}
}
}
r.reduceUncommittedSize(rd.CommittedEntries)
if len(rd.Entries) > 0 {
e := rd.Entries[len(rd.Entries)-1]
r.raftLog.stableTo(e.Index, e.Term)
}
if !IsEmptySnap(rd.Snapshot) {
r.raftLog.stableSnapTo(rd.Snapshot.Metadata.Index)
}
}
// maybeCommit attempts to advance the commit index. Returns true if
// the commit index changed (in which case the caller should call
// r.bcastAppend).
func (r *raft) maybeCommit() bool {
mci := r.prs.Committed()
return r.raftLog.maybeCommit(mci, r.Term)
}
func (r *raft) reset(term uint64) {
if r.Term != term {
r.Term = term
r.Vote = None
}
r.lead = None
r.electionElapsed = 0
r.heartbeatElapsed = 0
r.resetRandomizedElectionTimeout()
r.abortLeaderTransfer()
r.prs.ResetVotes()
r.prs.Visit(func(id uint64, pr *tracker.Progress) {
*pr = tracker.Progress{
Match: 0,
Next: r.raftLog.lastIndex() + 1,
Inflights: tracker.NewInflights(r.prs.MaxInflight),
IsLearner: pr.IsLearner,
}
if id == r.id {
pr.Match = r.raftLog.lastIndex()
}
})
r.pendingConfIndex = 0
r.uncommittedSize = 0
r.readOnly = newReadOnly(r.readOnly.option)
}
func (r *raft) appendEntry(es ...pb.Entry) (accepted bool) {
li := r.raftLog.lastIndex()
for i := range es {
es[i].Term = r.Term
es[i].Index = li + 1 + uint64(i)
}
// Track the size of this uncommitted proposal.
if !r.increaseUncommittedSize(es) {
r.logger.Debugf(
"%x appending new entries to log would exceed uncommitted entry size limit; dropping proposal",
r.id,
)
// Drop the proposal.
return false
}
// use latest "last" index after truncate/append
li = r.raftLog.append(es...)
r.prs.Progress[r.id].MaybeUpdate(li)
// Regardless of maybeCommit's return, our caller will call bcastAppend.
r.maybeCommit()
return true
}
// tickElection is run by followers and candidates after r.electionTimeout.
func (r *raft) tickElection() {
r.electionElapsed++
if r.promotable() && r.pastElectionTimeout() {
r.electionElapsed = 0
r.Step(pb.Message{From: r.id, Type: pb.MsgHup})
}
}
// tickHeartbeat is run by leaders to send a MsgBeat after r.heartbeatTimeout.
func (r *raft) tickHeartbeat() {
r.heartbeatElapsed++
r.electionElapsed++
if r.electionElapsed >= r.electionTimeout {
r.electionElapsed = 0
if r.checkQuorum {
r.Step(pb.Message{From: r.id, Type: pb.MsgCheckQuorum})
}
// If current leader cannot transfer leadership in electionTimeout, it becomes leader again.
if r.state == StateLeader && r.leadTransferee != None {
r.abortLeaderTransfer()
}
}
if r.state != StateLeader {
return
}
if r.heartbeatElapsed >= r.heartbeatTimeout {
r.heartbeatElapsed = 0
r.Step(pb.Message{From: r.id, Type: pb.MsgBeat})
}
}
func (r *raft) becomeFollower(term uint64, lead uint64) {
r.step = stepFollower
r.reset(term)
r.tick = r.tickElection
r.lead = lead
r.state = StateFollower
r.logger.Infof("%x became follower at term %d", r.id, r.Term)
}
func (r *raft) becomeCandidate() {
// TODO(xiangli) remove the panic when the raft implementation is stable
if r.state == StateLeader {
panic("invalid transition [leader -> candidate]")
}
r.step = stepCandidate
r.reset(r.Term + 1)
r.tick = r.tickElection
r.Vote = r.id
r.state = StateCandidate
r.logger.Infof("%x became candidate at term %d", r.id, r.Term)
}
func (r *raft) becomePreCandidate() {
// TODO(xiangli) remove the panic when the raft implementation is stable
if r.state == StateLeader {
panic("invalid transition [leader -> pre-candidate]")
}
// Becoming a pre-candidate changes our step functions and state,
// but doesn't change anything else. In particular it does not increase
// r.Term or change r.Vote.
r.step = stepCandidate
r.prs.ResetVotes()
r.tick = r.tickElection
r.lead = None
r.state = StatePreCandidate
r.logger.Infof("%x became pre-candidate at term %d", r.id, r.Term)
}
func (r *raft) becomeLeader() {
// TODO(xiangli) remove the panic when the raft implementation is stable
if r.state == StateFollower {
panic("invalid transition [follower -> leader]")
}
r.step = stepLeader
r.reset(r.Term)
r.tick = r.tickHeartbeat
r.lead = r.id
r.state = StateLeader
// Followers enter replicate mode when they've been successfully probed
// (perhaps after having received a snapshot as a result). The leader is
// trivially in this state. Note that r.reset() has initialized this
// progress with the last index already.
r.prs.Progress[r.id].BecomeReplicate()
// Conservatively set the pendingConfIndex to the last index in the
// log. There may or may not be a pending config change, but it's
// safe to delay any future proposals until we commit all our
// pending log entries, and scanning the entire tail of the log
// could be expensive.
r.pendingConfIndex = r.raftLog.lastIndex()
emptyEnt := pb.Entry{Data: nil}
if !r.appendEntry(emptyEnt) {
// This won't happen because we just called reset() above.
r.logger.Panic("empty entry was dropped")
}
// As a special case, don't count the initial empty entry towards the
// uncommitted log quota. This is because we want to preserve the
// behavior of allowing one entry larger than quota if the current
// usage is zero.
r.reduceUncommittedSize([]pb.Entry{emptyEnt})
r.logger.Infof("%x became leader at term %d", r.id, r.Term)
}
// campaign transitions the raft instance to candidate state. This must only be
// called after verifying that this is a legitimate transition.
func (r *raft) campaign(t CampaignType) {
if !r.promotable() {
// This path should not be hit (callers are supposed to check), but
// better safe than sorry.
r.logger.Warningf("%x is unpromotable; campaign() should have been called", r.id)
}
var term uint64
var voteMsg pb.MessageType
if t == campaignPreElection {
r.becomePreCandidate()
voteMsg = pb.MsgPreVote
// PreVote RPCs are sent for the next term before we've incremented r.Term.
term = r.Term + 1
} else {
r.becomeCandidate()
voteMsg = pb.MsgVote
term = r.Term
}
if _, _, res := r.poll(r.id, voteRespMsgType(voteMsg), true); res == quorum.VoteWon {
// We won the election after voting for ourselves (which must mean that
// this is a single-node cluster). Advance to the next state.
if t == campaignPreElection {
r.campaign(campaignElection)
} else {
r.becomeLeader()
}
return
}
var ids []uint64
{
idMap := r.prs.Voters.IDs()
ids = make([]uint64, 0, len(idMap))
for id := range idMap {
ids = append(ids, id)
}
sort.Slice(ids, func(i, j int) bool { return ids[i] < ids[j] })
}
for _, id := range ids {
if id == r.id {
continue
}
r.logger.Infof("%x [logterm: %d, index: %d] sent %s request to %x at term %d",
r.id, r.raftLog.lastTerm(), r.raftLog.lastIndex(), voteMsg, id, r.Term)
var ctx []byte
if t == campaignTransfer {
ctx = []byte(t)
}
r.send(pb.Message{Term: term, To: id, Type: voteMsg, Index: r.raftLog.lastIndex(), LogTerm: r.raftLog.lastTerm(), Context: ctx})
}
}
func (r *raft) poll(id uint64, t pb.MessageType, v bool) (granted int, rejected int, result quorum.VoteResult) {
if v {
r.logger.Infof("%x received %s from %x at term %d", r.id, t, id, r.Term)
} else {
r.logger.Infof("%x received %s rejection from %x at term %d", r.id, t, id, r.Term)
}
r.prs.RecordVote(id, v)
return r.prs.TallyVotes()
}
func (r *raft) Step(m pb.Message) error {
// Handle the message term, which may result in our stepping down to a follower.
switch {
case m.Term == 0:
// local message
case m.Term > r.Term:
if m.Type == pb.MsgVote || m.Type == pb.MsgPreVote {
force := bytes.Equal(m.Context, []byte(campaignTransfer))
inLease := r.checkQuorum && r.lead != None && r.electionElapsed < r.electionTimeout
if !force && inLease {
// If a server receives a RequestVote request within the minimum election timeout
// of hearing from a current leader, it does not update its term or grant its vote
r.logger.Infof("%x [logterm: %d, index: %d, vote: %x] ignored %s from %x [logterm: %d, index: %d] at term %d: lease is not expired (remaining ticks: %d)",
r.id, r.raftLog.lastTerm(), r.raftLog.lastIndex(), r.Vote, m.Type, m.From, m.LogTerm, m.Index, r.Term, r.electionTimeout-r.electionElapsed)
return nil
}
}
switch {
case m.Type == pb.MsgPreVote:
// Never change our term in response to a PreVote
case m.Type == pb.MsgPreVoteResp && !m.Reject:
// We send pre-vote requests with a term in our future. If the
// pre-vote is granted, we will increment our term when we get a
// quorum. If it is not, the term comes from the node that
// rejected our vote so we should become a follower at the new
// term.
default:
r.logger.Infof("%x [term: %d] received a %s message with higher term from %x [term: %d]",
r.id, r.Term, m.Type, m.From, m.Term)
if m.Type == pb.MsgApp || m.Type == pb.MsgHeartbeat || m.Type == pb.MsgSnap {
r.becomeFollower(m.Term, m.From)
} else {
r.becomeFollower(m.Term, None)
}
}
case m.Term < r.Term:
if (r.checkQuorum || r.preVote) && (m.Type == pb.MsgHeartbeat || m.Type == pb.MsgApp) {
// We have received messages from a leader at a lower term. It is possible
// that these messages were simply delayed in the network, but this could
// also mean that this node has advanced its term number during a network
// partition, and it is now unable to either win an election or to rejoin
// the majority on the old term. If checkQuorum is false, this will be
// handled by incrementing term numbers in response to MsgVote with a
// higher term, but if checkQuorum is true we may not advance the term on
// MsgVote and must generate other messages to advance the term. The net
// result of these two features is to minimize the disruption caused by
// nodes that have been removed from the cluster's configuration: a
// removed node will send MsgVotes (or MsgPreVotes) which will be ignored,
// but it will not receive MsgApp or MsgHeartbeat, so it will not create
// disruptive term increases, by notifying leader of this node's activeness.
// The above comments also true for Pre-Vote
//
// When follower gets isolated, it soon starts an election ending
// up with a higher term than leader, although it won't receive enough
// votes to win the election. When it regains connectivity, this response
// with "pb.MsgAppResp" of higher term would force leader to step down.
// However, this disruption is inevitable to free this stuck node with
// fresh election. This can be prevented with Pre-Vote phase.
r.send(pb.Message{To: m.From, Type: pb.MsgAppResp})
} else if m.Type == pb.MsgPreVote {
// Before Pre-Vote enable, there may have candidate with higher term,
// but less log. After update to Pre-Vote, the cluster may deadlock if
// we drop messages with a lower term.
r.logger.Infof("%x [logterm: %d, index: %d, vote: %x] rejected %s from %x [logterm: %d, index: %d] at term %d",
r.id, r.raftLog.lastTerm(), r.raftLog.lastIndex(), r.Vote, m.Type, m.From, m.LogTerm, m.Index, r.Term)
r.send(pb.Message{To: m.From, Term: r.Term, Type: pb.MsgPreVoteResp, Reject: true})
} else {
// ignore other cases
r.logger.Infof("%x [term: %d] ignored a %s message with lower term from %x [term: %d]",
r.id, r.Term, m.Type, m.From, m.Term)
}
return nil
}
switch m.Type {
case pb.MsgHup:
if r.state != StateLeader {
if !r.promotable() {
r.logger.Warningf("%x is unpromotable and can not campaign; ignoring MsgHup", r.id)
return nil
}
ents, err := r.raftLog.slice(r.raftLog.applied+1, r.raftLog.committed+1, noLimit)
if err != nil {
r.logger.Panicf("unexpected error getting unapplied entries (%v)", err)
}
if n := numOfPendingConf(ents); n != 0 && r.raftLog.committed > r.raftLog.applied {
r.logger.Warningf("%x cannot campaign at term %d since there are still %d pending configuration changes to apply", r.id, r.Term, n)
return nil
}
r.logger.Infof("%x is starting a new election at term %d", r.id, r.Term)
if r.preVote {
r.campaign(campaignPreElection)
} else {
r.campaign(campaignElection)
}
} else {
r.logger.Debugf("%x ignoring MsgHup because already leader", r.id)
}
case pb.MsgVote, pb.MsgPreVote:
// We can vote if this is a repeat of a vote we've already cast...
canVote := r.Vote == m.From ||
// ...we haven't voted and we don't think there's a leader yet in this term...
(r.Vote == None && r.lead == None) ||
// ...or this is a PreVote for a future term...
(m.Type == pb.MsgPreVote && m.Term > r.Term)
// ...and we believe the candidate is up to date.
if canVote && r.raftLog.isUpToDate(m.Index, m.LogTerm) {
// Note: it turns out that that learners must be allowed to cast votes.
// This seems counter- intuitive but is necessary in the situation in which
// a learner has been promoted (i.e. is now a voter) but has not learned
// about this yet.
// For example, consider a group in which id=1 is a learner and id=2 and
// id=3 are voters. A configuration change promoting 1 can be committed on
// the quorum `{2,3}` without the config change being appended to the
// learner's log. If the leader (say 2) fails, there are de facto two
// voters remaining. Only 3 can win an election (due to its log containing
// all committed entries), but to do so it will need 1 to vote. But 1
// considers itself a learner and will continue to do so until 3 has
// stepped up as leader, replicates the conf change to 1, and 1 applies it.
// Ultimately, by receiving a request to vote, the learner realizes that
// the candidate believes it to be a voter, and that it should act
// accordingly. The candidate's config may be stale, too; but in that case
// it won't win the election, at least in the absence of the bug discussed
// in:
// https://github.com/etcd-io/etcd/issues/7625#issuecomment-488798263.
r.logger.Infof("%x [logterm: %d, index: %d, vote: %x] cast %s for %x [logterm: %d, index: %d] at term %d",
r.id, r.raftLog.lastTerm(), r.raftLog.lastIndex(), r.Vote, m.Type, m.From, m.LogTerm, m.Index, r.Term)
// When responding to Msg{Pre,}Vote messages we include the term
// from the message, not the local term. To see why, consider the
// case where a single node was previously partitioned away and
// it's local term is now out of date. If we include the local term
// (recall that for pre-votes we don't update the local term), the
// (pre-)campaigning node on the other end will proceed to ignore
// the message (it ignores all out of date messages).
// The term in the original message and current local term are the
// same in the case of regular votes, but different for pre-votes.
r.send(pb.Message{To: m.From, Term: m.Term, Type: voteRespMsgType(m.Type)})
if m.Type == pb.MsgVote {
// Only record real votes.
r.electionElapsed = 0
r.Vote = m.From
}
} else {
r.logger.Infof("%x [logterm: %d, index: %d, vote: %x] rejected %s from %x [logterm: %d, index: %d] at term %d",
r.id, r.raftLog.lastTerm(), r.raftLog.lastIndex(), r.Vote, m.Type, m.From, m.LogTerm, m.Index, r.Term)
r.send(pb.Message{To: m.From, Term: r.Term, Type: voteRespMsgType(m.Type), Reject: true})
}
default:
err := r.step(r, m)
if err != nil {
return err
}
}
return nil
}
type stepFunc func(r *raft, m pb.Message) error
func stepLeader(r *raft, m pb.Message) error {
// These message types do not require any progress for m.From.
switch m.Type {
case pb.MsgBeat:
r.bcastHeartbeat()
return nil
case pb.MsgCheckQuorum:
// The leader should always see itself as active. As a precaution, handle
// the case in which the leader isn't in the configuration any more (for
// example if it just removed itself).
//
// TODO(tbg): I added a TODO in removeNode, it doesn't seem that the
// leader steps down when removing itself. I might be missing something.
if pr := r.prs.Progress[r.id]; pr != nil {
pr.RecentActive = true
}
if !r.prs.QuorumActive() {
r.logger.Warningf("%x stepped down to follower since quorum is not active", r.id)
r.becomeFollower(r.Term, None)
}
// Mark everyone (but ourselves) as inactive in preparation for the next
// CheckQuorum.
r.prs.Visit(func(id uint64, pr *tracker.Progress) {
if id != r.id {
pr.RecentActive = false
}
})
return nil
case pb.MsgProp:
if len(m.Entries) == 0 {
r.logger.Panicf("%x stepped empty MsgProp", r.id)
}
if r.prs.Progress[r.id] == nil {
// If we are not currently a member of the range (i.e. this node
// was removed from the configuration while serving as leader),
// drop any new proposals.
return ErrProposalDropped
}
if r.leadTransferee != None {
r.logger.Debugf("%x [term %d] transfer leadership to %x is in progress; dropping proposal", r.id, r.Term, r.leadTransferee)
return ErrProposalDropped
}
for i := range m.Entries {
e := &m.Entries[i]
var cc pb.ConfChangeI
if e.Type == pb.EntryConfChange {
var ccc pb.ConfChange
if err := ccc.Unmarshal(e.Data); err != nil {
panic(err)
}
cc = ccc
} else if e.Type == pb.EntryConfChangeV2 {
var ccc pb.ConfChangeV2
if err := ccc.Unmarshal(e.Data); err != nil {
panic(err)
}
cc = ccc
}
if cc != nil {
alreadyPending := r.pendingConfIndex > r.raftLog.applied
alreadyJoint := len(r.prs.Config.Voters[1]) > 0
wantsLeaveJoint := len(cc.AsV2().Changes) == 0
var refused string
if alreadyPending {
refused = fmt.Sprintf("possible unapplied conf change at index %d (applied to %d)", r.pendingConfIndex, r.raftLog.applied)
} else if alreadyJoint && !wantsLeaveJoint {
refused = "must transition out of joint config first"
} else if !alreadyJoint && wantsLeaveJoint {
refused = "not in joint state; refusing empty conf change"
}
if refused != "" {
r.logger.Infof("%x ignoring conf change %v at config %s: %s", r.id, cc, r.prs.Config, refused)
m.Entries[i] = pb.Entry{Type: pb.EntryNormal}
} else {
r.pendingConfIndex = r.raftLog.lastIndex() + uint64(i) + 1
}
}
}
if !r.appendEntry(m.Entries...) {
return ErrProposalDropped
}
r.bcastAppend()
return nil
case pb.MsgReadIndex:
// If more than the local vote is needed, go through a full broadcast,
// otherwise optimize.
if !r.prs.IsSingleton() {
if r.raftLog.zeroTermOnErrCompacted(r.raftLog.term(r.raftLog.committed)) != r.Term {
// Reject read only request when this leader has not committed any log entry at its term.
return nil
}
// thinking: use an interally defined context instead of the user given context.
// We can express this in terms of the term and index instead of a user-supplied value.
// This would allow multiple reads to piggyback on the same message.
switch r.readOnly.option {
case ReadOnlySafe:
r.readOnly.addRequest(r.raftLog.committed, m)
// The local node automatically acks the request.
r.readOnly.recvAck(r.id, m.Entries[0].Data)
r.bcastHeartbeatWithCtx(m.Entries[0].Data)
case ReadOnlyLeaseBased:
ri := r.raftLog.committed
if m.From == None || m.From == r.id { // from local member
r.readStates = append(r.readStates, ReadState{Index: ri, RequestCtx: m.Entries[0].Data})
} else {
r.send(pb.Message{To: m.From, Type: pb.MsgReadIndexResp, Index: ri, Entries: m.Entries})
}
}
} else { // only one voting member (the leader) in the cluster
if m.From == None || m.From == r.id { // from leader itself
r.readStates = append(r.readStates, ReadState{Index: r.raftLog.committed, RequestCtx: m.Entries[0].Data})
} else { // from learner member
r.send(pb.Message{To: m.From, Type: pb.MsgReadIndexResp, Index: r.raftLog.committed, Entries: m.Entries})
}
}
return nil
}
// All other message types require a progress for m.From (pr).
pr := r.prs.Progress[m.From]
if pr == nil {
r.logger.Debugf("%x no progress available for %x", r.id, m.From)
return nil
}
switch m.Type {
case pb.MsgAppResp:
pr.RecentActive = true
if m.Reject {
r.logger.Debugf("%x received MsgAppResp(MsgApp was rejected, lastindex: %d) from %x for index %d",
r.id, m.RejectHint, m.From, m.Index)
if pr.MaybeDecrTo(m.Index, m.RejectHint) {
r.logger.Debugf("%x decreased progress of %x to [%s]", r.id, m.From, pr)
if pr.State == tracker.StateReplicate {
pr.BecomeProbe()
}
r.sendAppend(m.From)
}
} else {
oldPaused := pr.IsPaused()
if pr.MaybeUpdate(m.Index) {
switch {
case pr.State == tracker.StateProbe:
pr.BecomeReplicate()
case pr.State == tracker.StateSnapshot && pr.Match >= pr.PendingSnapshot:
// TODO(tbg): we should also enter this branch if a snapshot is
// received that is below pr.PendingSnapshot but which makes it
// possible to use the log again.
r.logger.Debugf("%x recovered from needing snapshot, resumed sending replication messages to %x [%s]", r.id, m.From, pr)
// Transition back to replicating state via probing state
// (which takes the snapshot into account). If we didn't
// move to replicating state, that would only happen with
// the next round of appends (but there may not be a next
// round for a while, exposing an inconsistent RaftStatus).
pr.BecomeProbe()
pr.BecomeReplicate()
case pr.State == tracker.StateReplicate:
pr.Inflights.FreeLE(m.Index)
}
if r.maybeCommit() {
r.bcastAppend()
} else if oldPaused {
// If we were paused before, this node may be missing the
// latest commit index, so send it.
r.sendAppend(m.From)
}
// We've updated flow control information above, which may
// allow us to send multiple (size-limited) in-flight messages
// at once (such as when transitioning from probe to
// replicate, or when freeTo() covers multiple messages). If
// we have more entries to send, send as many messages as we
// can (without sending empty messages for the commit index)
for r.maybeSendAppend(m.From, false) {
}
// Transfer leadership is in progress.
if m.From == r.leadTransferee && pr.Match == r.raftLog.lastIndex() {
r.logger.Infof("%x sent MsgTimeoutNow to %x after received MsgAppResp", r.id, m.From)
r.sendTimeoutNow(m.From)
}
}
}
case pb.MsgHeartbeatResp:
pr.RecentActive = true
pr.ProbeSent = false
// free one slot for the full inflights window to allow progress.
if pr.State == tracker.StateReplicate && pr.Inflights.Full() {
pr.Inflights.FreeFirstOne()
}
if pr.Match < r.raftLog.lastIndex() {
r.sendAppend(m.From)
}
if r.readOnly.option != ReadOnlySafe || len(m.Context) == 0 {
return nil
}
if r.prs.Voters.VoteResult(r.readOnly.recvAck(m.From, m.Context)) != quorum.VoteWon {
return nil
}
rss := r.readOnly.advance(m)
for _, rs := range rss {
req := rs.req
if req.From == None || req.From == r.id { // from local member
r.readStates = append(r.readStates, ReadState{Index: rs.index, RequestCtx: req.Entries[0].Data})
} else {
r.send(pb.Message{To: req.From, Type: pb.MsgReadIndexResp, Index: rs.index, Entries: req.Entries})
}
}
case pb.MsgSnapStatus:
if pr.State != tracker.StateSnapshot {
return nil
}
// TODO(tbg): this code is very similar to the snapshot handling in
// MsgAppResp above. In fact, the code there is more correct than the
// code here and should likely be updated to match (or even better, the
// logic pulled into a newly created Progress state machine handler).
if !m.Reject {
pr.BecomeProbe()
r.logger.Debugf("%x snapshot succeeded, resumed sending replication messages to %x [%s]", r.id, m.From, pr)
} else {
// NB: the order here matters or we'll be probing erroneously from
// the snapshot index, but the snapshot never applied.
pr.PendingSnapshot = 0
pr.BecomeProbe()
r.logger.Debugf("%x snapshot failed, resumed sending replication messages to %x [%s]", r.id, m.From, pr)
}
// If snapshot finish, wait for the MsgAppResp from the remote node before sending
// out the next MsgApp.
// If snapshot failure, wait for a heartbeat interval before next try
pr.ProbeSent = true
case pb.MsgUnreachable:
// During optimistic replication, if the remote becomes unreachable,
// there is huge probability that a MsgApp is lost.
if pr.State == tracker.StateReplicate {
pr.BecomeProbe()
}
r.logger.Debugf("%x failed to send message to %x because it is unreachable [%s]", r.id, m.From, pr)
case pb.MsgTransferLeader:
if pr.IsLearner {
r.logger.Debugf("%x is learner. Ignored transferring leadership", r.id)
return nil
}
leadTransferee := m.From
lastLeadTransferee := r.leadTransferee
if lastLeadTransferee != None {
if lastLeadTransferee == leadTransferee {
r.logger.Infof("%x [term %d] transfer leadership to %x is in progress, ignores request to same node %x",
r.id, r.Term, leadTransferee, leadTransferee)
return nil
}
r.abortLeaderTransfer()
r.logger.Infof("%x [term %d] abort previous transferring leadership to %x", r.id, r.Term, lastLeadTransferee)
}
if leadTransferee == r.id {
r.logger.Debugf("%x is already leader. Ignored transferring leadership to self", r.id)
return nil
}
// Transfer leadership to third party.
r.logger.Infof("%x [term %d] starts to transfer leadership to %x", r.id, r.Term, leadTransferee)
// Transfer leadership should be finished in one electionTimeout, so reset r.electionElapsed.
r.electionElapsed = 0
r.leadTransferee = leadTransferee
if pr.Match == r.raftLog.lastIndex() {
r.sendTimeoutNow(leadTransferee)
r.logger.Infof("%x sends MsgTimeoutNow to %x immediately as %x already has up-to-date log", r.id, leadTransferee, leadTransferee)
} else {
r.sendAppend(leadTransferee)
}
}
return nil
}
// stepCandidate is shared by StateCandidate and StatePreCandidate; the difference is
// whether they respond to MsgVoteResp or MsgPreVoteResp.
func stepCandidate(r *raft, m pb.Message) error {
// Only handle vote responses corresponding to our candidacy (while in
// StateCandidate, we may get stale MsgPreVoteResp messages in this term from
// our pre-candidate state).
var myVoteRespType pb.MessageType
if r.state == StatePreCandidate {
myVoteRespType = pb.MsgPreVoteResp
} else {
myVoteRespType = pb.MsgVoteResp
}
switch m.Type {
case pb.MsgProp:
r.logger.Infof("%x no leader at term %d; dropping proposal", r.id, r.Term)
return ErrProposalDropped
case pb.MsgApp:
r.becomeFollower(m.Term, m.From) // always m.Term == r.Term
r.handleAppendEntries(m)
case pb.MsgHeartbeat:
r.becomeFollower(m.Term, m.From) // always m.Term == r.Term
r.handleHeartbeat(m)
case pb.MsgSnap:
r.becomeFollower(m.Term, m.From) // always m.Term == r.Term
r.handleSnapshot(m)
case myVoteRespType:
gr, rj, res := r.poll(m.From, m.Type, !m.Reject)
r.logger.Infof("%x has received %d %s votes and %d vote rejections", r.id, gr, m.Type, rj)
switch res {
case quorum.VoteWon:
if r.state == StatePreCandidate {
r.campaign(campaignElection)
} else {
r.becomeLeader()
r.bcastAppend()
}
case quorum.VoteLost:
// pb.MsgPreVoteResp contains future term of pre-candidate
// m.Term > r.Term; reuse r.Term
r.becomeFollower(r.Term, None)
}
case pb.MsgTimeoutNow:
r.logger.Debugf("%x [term %d state %v] ignored MsgTimeoutNow from %x", r.id, r.Term, r.state, m.From)
}
return nil
}
func stepFollower(r *raft, m pb.Message) error {
switch m.Type {
case pb.MsgProp:
if r.lead == None {
r.logger.Infof("%x no leader at term %d; dropping proposal", r.id, r.Term)
return ErrProposalDropped
} else if r.disableProposalForwarding {
r.logger.Infof("%x not forwarding to leader %x at term %d; dropping proposal", r.id, r.lead, r.Term)
return ErrProposalDropped
}
m.To = r.lead
r.send(m)
case pb.MsgApp:
r.electionElapsed = 0
r.lead = m.From
r.handleAppendEntries(m)
case pb.MsgHeartbeat:
r.electionElapsed = 0
r.lead = m.From
r.handleHeartbeat(m)
case pb.MsgSnap:
r.electionElapsed = 0
r.lead = m.From
r.handleSnapshot(m)
case pb.MsgTransferLeader:
if r.lead == None {
r.logger.Infof("%x no leader at term %d; dropping leader transfer msg", r.id, r.Term)
return nil
}
m.To = r.lead
r.send(m)
case pb.MsgTimeoutNow:
if r.promotable() {
r.logger.Infof("%x [term %d] received MsgTimeoutNow from %x and starts an election to get leadership.", r.id, r.Term, m.From)
// Leadership transfers never use pre-vote even if r.preVote is true; we
// know we are not recovering from a partition so there is no need for the
// extra round trip.
r.campaign(campaignTransfer)
} else {
r.logger.Infof("%x received MsgTimeoutNow from %x but is not promotable", r.id, m.From)
}
case pb.MsgReadIndex:
if r.lead == None {
r.logger.Infof("%x no leader at term %d; dropping index reading msg", r.id, r.Term)
return nil
}
m.To = r.lead
r.send(m)
case pb.MsgReadIndexResp:
if len(m.Entries) != 1 {
r.logger.Errorf("%x invalid format of MsgReadIndexResp from %x, entries count: %d", r.id, m.From, len(m.Entries))
return nil
}
r.readStates = append(r.readStates, ReadState{Index: m.Index, RequestCtx: m.Entries[0].Data})
}
return nil
}
func (r *raft) handleAppendEntries(m pb.Message) {
if m.Index < r.raftLog.committed {
r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.committed})
return
}
if mlastIndex, ok := r.raftLog.maybeAppend(m.Index, m.LogTerm, m.Commit, m.Entries...); ok {
r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: mlastIndex})
} else {
r.logger.Debugf("%x [logterm: %d, index: %d] rejected MsgApp [logterm: %d, index: %d] from %x",
r.id, r.raftLog.zeroTermOnErrCompacted(r.raftLog.term(m.Index)), m.Index, m.LogTerm, m.Index, m.From)
r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: m.Index, Reject: true, RejectHint: r.raftLog.lastIndex()})
}
}
func (r *raft) handleHeartbeat(m pb.Message) {
r.raftLog.commitTo(m.Commit)
r.send(pb.Message{To: m.From, Type: pb.MsgHeartbeatResp, Context: m.Context})
}
func (r *raft) handleSnapshot(m pb.Message) {
sindex, sterm := m.Snapshot.Metadata.Index, m.Snapshot.Metadata.Term
if r.restore(m.Snapshot) {
r.logger.Infof("%x [commit: %d] restored snapshot [index: %d, term: %d]",
r.id, r.raftLog.committed, sindex, sterm)
r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.lastIndex()})
} else {
r.logger.Infof("%x [commit: %d] ignored snapshot [index: %d, term: %d]",
r.id, r.raftLog.committed, sindex, sterm)
r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.committed})
}
}
// restore recovers the state machine from a snapshot. It restores the log and the
// configuration of state machine. If this method returns false, the snapshot was
// ignored, either because it was obsolete or because of an error.
func (r *raft) restore(s pb.Snapshot) bool {
if s.Metadata.Index <= r.raftLog.committed {
return false
}
if r.state != StateFollower {
// This is defense-in-depth: if the leader somehow ended up applying a
// snapshot, it could move into a new term without moving into a
// follower state. This should never fire, but if it did, we'd have
// prevented damage by returning early, so log only a loud warning.
//
// At the time of writing, the instance is guaranteed to be in follower
// state when this method is called.
r.logger.Warningf("%x attempted to restore snapshot as leader; should never happen", r.id)
r.becomeFollower(r.Term+1, None)
return false
}
// More defense-in-depth: throw away snapshot if recipient is not in the
// config. This shouuldn't ever happen (at the time of writing) but lots of
// code here and there assumes that r.id is in the progress tracker.
found := false
cs := s.Metadata.ConfState
for _, set := range [][]uint64{
cs.Voters,
cs.Learners,
} {
for _, id := range set {
if id == r.id {
found = true
break
}
}
}
if !found {
r.logger.Warningf(
"%x attempted to restore snapshot but it is not in the ConfState %v; should never happen",
r.id, cs,
)
return false
}
// Now go ahead and actually restore.
if r.raftLog.matchTerm(s.Metadata.Index, s.Metadata.Term) {
r.logger.Infof("%x [commit: %d, lastindex: %d, lastterm: %d] fast-forwarded commit to snapshot [index: %d, term: %d]",
r.id, r.raftLog.committed, r.raftLog.lastIndex(), r.raftLog.lastTerm(), s.Metadata.Index, s.Metadata.Term)
r.raftLog.commitTo(s.Metadata.Index)
return false
}
r.raftLog.restore(s)
// Reset the configuration and add the (potentially updated) peers in anew.
r.prs = tracker.MakeProgressTracker(r.prs.MaxInflight)
cfg, prs, err := confchange.Restore(confchange.Changer{
Tracker: r.prs,
LastIndex: r.raftLog.lastIndex(),
}, cs)
if err != nil {
// This should never happen. Either there's a bug in our config change
// handling or the client corrupted the conf change.
panic(fmt.Sprintf("unable to restore config %+v: %s", cs, err))
}
assertConfStatesEquivalent(r.logger, cs, r.switchToConfig(cfg, prs))
pr := r.prs.Progress[r.id]
pr.MaybeUpdate(pr.Next - 1) // TODO(tbg): this is untested and likely unneeded
r.logger.Infof("%x [commit: %d, lastindex: %d, lastterm: %d] restored snapshot [index: %d, term: %d]",
r.id, r.raftLog.committed, r.raftLog.lastIndex(), r.raftLog.lastTerm(), s.Metadata.Index, s.Metadata.Term)
return true
}
// promotable indicates whether state machine can be promoted to leader,
// which is true when its own id is in progress list.
func (r *raft) promotable() bool {
pr := r.prs.Progress[r.id]
return pr != nil && !pr.IsLearner
}
func (r *raft) applyConfChange(cc pb.ConfChangeV2) pb.ConfState {
cfg, prs, err := func() (tracker.Config, tracker.ProgressMap, error) {
changer := confchange.Changer{
Tracker: r.prs,
LastIndex: r.raftLog.lastIndex(),
}
if cc.LeaveJoint() {
return changer.LeaveJoint()
} else if autoLeave, ok := cc.EnterJoint(); ok {
return changer.EnterJoint(autoLeave, cc.Changes...)
}
return changer.Simple(cc.Changes...)
}()
if err != nil {
// TODO(tbg): return the error to the caller.
panic(err)
}
return r.switchToConfig(cfg, prs)
}
// switchToConfig reconfigures this node to use the provided configuration. It
// updates the in-memory state and, when necessary, carries out additional
// actions such as reacting to the removal of nodes or changed quorum
// requirements.
//
// The inputs usually result from restoring a ConfState or applying a ConfChange.
func (r *raft) switchToConfig(cfg tracker.Config, prs tracker.ProgressMap) pb.ConfState {
r.prs.Config = cfg
r.prs.Progress = prs
r.logger.Infof("%x switched to configuration %s", r.id, r.prs.Config)
cs := r.prs.ConfState()
pr, ok := r.prs.Progress[r.id]
// Update whether the node itself is a learner, resetting to false when the
// node is removed.
r.isLearner = ok && pr.IsLearner
if (!ok || r.isLearner) && r.state == StateLeader {
// This node is leader and was removed or demoted. We prevent demotions
// at the time writing but hypothetically we handle them the same way as
// removing the leader: stepping down into the next Term.
//
// TODO(tbg): step down (for sanity) and ask follower with largest Match
// to TimeoutNow (to avoid interruption). This might still drop some
// proposals but it's better than nothing.
//
// TODO(tbg): test this branch. It is untested at the time of writing.
return cs
}
// The remaining steps only make sense if this node is the leader and there
// are other nodes.
if r.state != StateLeader || len(cs.Voters) == 0 {
return cs
}
if r.maybeCommit() {
// If the configuration change means that more entries are committed now,
// broadcast/append to everyone in the updated config.
r.bcastAppend()
} else {
// Otherwise, still probe the newly added replicas; there's no reason to
// let them wait out a heartbeat interval (or the next incoming
// proposal).
r.prs.Visit(func(id uint64, pr *tracker.Progress) {
r.maybeSendAppend(id, false /* sendIfEmpty */)
})
}
// If the the leadTransferee was removed, abort the leadership transfer.
if _, tOK := r.prs.Progress[r.leadTransferee]; !tOK && r.leadTransferee != 0 {
r.abortLeaderTransfer()
}
return cs
}
func (r *raft) loadState(state pb.HardState) {
if state.Commit < r.raftLog.committed || state.Commit > r.raftLog.lastIndex() {
r.logger.Panicf("%x state.commit %d is out of range [%d, %d]", r.id, state.Commit, r.raftLog.committed, r.raftLog.lastIndex())
}
r.raftLog.committed = state.Commit
r.Term = state.Term
r.Vote = state.Vote
}
// pastElectionTimeout returns true iff r.electionElapsed is greater
// than or equal to the randomized election timeout in
// [electiontimeout, 2 * electiontimeout - 1].
func (r *raft) pastElectionTimeout() bool {
return r.electionElapsed >= r.randomizedElectionTimeout
}
func (r *raft) resetRandomizedElectionTimeout() {
r.randomizedElectionTimeout = r.electionTimeout + globalRand.Intn(r.electionTimeout)
}
func (r *raft) sendTimeoutNow(to uint64) {
r.send(pb.Message{To: to, Type: pb.MsgTimeoutNow})
}
func (r *raft) abortLeaderTransfer() {
r.leadTransferee = None
}
// increaseUncommittedSize computes the size of the proposed entries and
// determines whether they would push leader over its maxUncommittedSize limit.
// If the new entries would exceed the limit, the method returns false. If not,
// the increase in uncommitted entry size is recorded and the method returns
// true.
func (r *raft) increaseUncommittedSize(ents []pb.Entry) bool {
var s uint64
for _, e := range ents {
s += uint64(PayloadSize(e))
}
if r.uncommittedSize > 0 && r.uncommittedSize+s > r.maxUncommittedSize {
// If the uncommitted tail of the Raft log is empty, allow any size
// proposal. Otherwise, limit the size of the uncommitted tail of the
// log and drop any proposal that would push the size over the limit.
return false
}
r.uncommittedSize += s
return true
}
// reduceUncommittedSize accounts for the newly committed entries by decreasing
// the uncommitted entry size limit.
func (r *raft) reduceUncommittedSize(ents []pb.Entry) {
if r.uncommittedSize == 0 {
// Fast-path for followers, who do not track or enforce the limit.
return
}
var s uint64
for _, e := range ents {
s += uint64(PayloadSize(e))
}
if s > r.uncommittedSize {
// uncommittedSize may underestimate the size of the uncommitted Raft
// log tail but will never overestimate it. Saturate at 0 instead of
// allowing overflow.
r.uncommittedSize = 0
} else {
r.uncommittedSize -= s
}
}
func numOfPendingConf(ents []pb.Entry) int {
n := 0
for i := range ents {
if ents[i].Type == pb.EntryConfChange {
n++
}
}
return n
}