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raft.go
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raft.go
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// 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"
"crypto/rand"
"errors"
"fmt"
"math"
"math/big"
"sort"
"strings"
"sync"
"go.etcd.io/raft/v3/confchange"
"go.etcd.io/raft/v3/quorum"
pb "go.etcd.io/raft/v3/raftpb"
"go.etcd.io/raft/v3/tracker"
)
const (
// None is a placeholder node ID used when there is no leader.
None uint64 = 0
// LocalAppendThread is a reference to a local thread that saves unstable
// log entries and snapshots to stable storage. The identifier is used as a
// target for MsgStorageAppend messages when AsyncStorageWrites is enabled.
LocalAppendThread uint64 = math.MaxUint64
// LocalApplyThread is a reference to a local thread that applies committed
// log entries to the local state machine. The identifier is used as a
// target for MsgStorageApply messages when AsyncStorageWrites is enabled.
LocalApplyThread uint64 = math.MaxUint64 - 1
)
// 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"
)
const noLimit = math.MaxUint64
// 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
}
func (r *lockedRand) Intn(n int) int {
r.mu.Lock()
v, _ := rand.Int(rand.Reader, big.NewInt(int64(n)))
r.mu.Unlock()
return int(v.Int64())
}
var globalRand = &lockedRand{}
// 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[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
// 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
// AsyncStorageWrites configures the raft node to write to its local storage
// (raft log and state machine) using a request/response message passing
// interface instead of the default Ready/Advance function call interface.
// Local storage messages can be pipelined and processed asynchronously
// (with respect to Ready iteration), facilitating reduced interference
// between Raft proposals and increased batching of log appends and state
// machine application. As a result, use of asynchronous storage writes can
// reduce end-to-end commit latency and increase maximum throughput.
//
// When true, the Ready.Message slice will include MsgStorageAppend and
// MsgStorageApply messages. The messages will target a LocalAppendThread
// and a LocalApplyThread, respectively. Messages to the same target must be
// reliably processed in order. In other words, they can't be dropped (like
// messages over the network) and those targeted at the same thread can't be
// reordered. Messages to different targets can be processed in any order.
//
// MsgStorageAppend carries Raft log entries to append, election votes /
// term changes / updated commit indexes to persist, and snapshots to apply.
// All writes performed in service of a MsgStorageAppend must be durable
// before response messages are delivered. However, if the MsgStorageAppend
// carries no response messages, durability is not required. The message
// assumes the role of the Entries, HardState, and Snapshot fields in Ready.
//
// MsgStorageApply carries committed entries to apply. Writes performed in
// service of a MsgStorageApply need not be durable before response messages
// are delivered. The message assumes the role of the CommittedEntries field
// in Ready.
//
// Local messages each carry one or more response messages which should be
// delivered after the corresponding storage write has been completed. These
// responses may target the same node or may target other nodes. The storage
// threads are not responsible for understanding the response messages, only
// for delivering them to the correct target after performing the storage
// write.
AsyncStorageWrites bool
// 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 applying at the same time.
//
// Despite its name (preserved for compatibility), this quota applies across
// Ready structs to encompass all outstanding entries in unacknowledged
// MsgStorageApply messages when AsyncStorageWrites is enabled.
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
// MaxInflightBytes limits the number of in-flight bytes in append messages.
// Complements MaxInflightMsgs. Ignored if zero.
//
// This effectively bounds the bandwidth-delay product. Note that especially
// in high-latency deployments setting this too low can lead to a dramatic
// reduction in throughput. For example, with a peer that has a round-trip
// latency of 100ms to the leader and this setting is set to 1 MB, there is a
// throughput limit of 10 MB/s for this group. With RTT of 400ms, this drops
// to 2.5 MB/s. See Little's law to understand the maths behind.
MaxInflightBytes uint64
// 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 IsLocalMsgTarget(c.ID) {
return errors.New("cannot use local target 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.MaxInflightBytes == 0 {
c.MaxInflightBytes = noLimit
} else if c.MaxInflightBytes < c.MaxSizePerMsg {
return errors.New("max inflight bytes must be >= max message size")
}
if c.Logger == nil {
c.Logger = getLogger()
}
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 entryEncodingSize
maxUncommittedSize entryPayloadSize
// TODO(tbg): rename to trk.
prs tracker.ProgressTracker
state StateType
// isLearner is true if the local raft node is a learner.
isLearner bool
// msgs contains the list of messages that should be sent out immediately to
// other nodes.
//
// Messages in this list must target other nodes.
msgs []pb.Message
// msgsAfterAppend contains the list of messages that should be sent after
// the accumulated unstable state (e.g. term, vote, []entry, and snapshot)
// has been persisted to durable storage. This includes waiting for any
// unstable state that is already in the process of being persisted (i.e.
// has already been handed out in a prior Ready struct) to complete.
//
// Messages in this list may target other nodes or may target this node.
//
// Messages in this list have the type MsgAppResp, MsgVoteResp, or
// MsgPreVoteResp. See the comment in raft.send for details.
msgsAfterAppend []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 entryPayloadSize
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
// pendingReadIndexMessages is used to store messages of type MsgReadIndex
// that can't be answered as new leader didn't committed any log in
// current term. Those will be handled as fast as first log is committed in
// current term.
pendingReadIndexMessages []pb.Message
}
func newRaft(c *Config) *raft {
if err := c.validate(); err != nil {
panic(err.Error())
}
raftlog := newLogWithSize(c.Storage, c.Logger, entryEncodingSize(c.MaxCommittedSizePerReady))
hs, cs, err := c.Storage.InitialState()
if err != nil {
panic(err) // TODO(bdarnell)
}
r := &raft{
id: c.ID,
lead: None,
isLearner: false,
raftLog: raftlog,
maxMsgSize: entryEncodingSize(c.MaxSizePerMsg),
maxUncommittedSize: entryPayloadSize(c.MaxUncommittedEntriesSize),
prs: tracker.MakeProgressTracker(c.MaxInflightMsgs, c.MaxInflightBytes),
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, 0 /* size */)
}
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 schedules persisting state to a stable storage and AFTER that
// sending the message (as part of next Ready message processing).
func (r *raft) send(m pb.Message) {
if m.From == None {
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
r.logger.Panicf("term should be set when sending %s", m.Type)
}
} else {
if m.Term != 0 {
r.logger.Panicf("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
}
}
if m.Type == pb.MsgAppResp || m.Type == pb.MsgVoteResp || m.Type == pb.MsgPreVoteResp {
// If async storage writes are enabled, messages added to the msgs slice
// are allowed to be sent out before unstable state (e.g. log entry
// writes and election votes) have been durably synced to the local
// disk.
//
// For most message types, this is not an issue. However, response
// messages that relate to "voting" on either leader election or log
// appends require durability before they can be sent. It would be
// incorrect to publish a vote in an election before that vote has been
// synced to stable storage locally. Similarly, it would be incorrect to
// acknowledge a log append to the leader before that entry has been
// synced to stable storage locally.
//
// Per the Raft thesis, section 3.8 Persisted state and server restarts:
//
// > Raft servers must persist enough information to stable storage to
// > survive server restarts safely. In particular, each server persists
// > its current term and vote; this is necessary to prevent the server
// > from voting twice in the same term or replacing log entries from a
// > newer leader with those from a deposed leader. Each server also
// > persists new log entries before they are counted towards the entries’
// > commitment; this prevents committed entries from being lost or
// > “uncommitted” when servers restart
//
// To enforce this durability requirement, these response messages are
// queued to be sent out as soon as the current collection of unstable
// state (the state that the response message was predicated upon) has
// been durably persisted. This unstable state may have already been
// passed to a Ready struct whose persistence is in progress or may be
// waiting for the next Ready struct to begin being written to Storage.
// These messages must wait for all of this state to be durable before
// being published.
//
// Rejected responses (m.Reject == true) present an interesting case
// where the durability requirement is less unambiguous. A rejection may
// be predicated upon unstable state. For instance, a node may reject a
// vote for one peer because it has already begun syncing its vote for
// another peer. Or it may reject a vote from one peer because it has
// unstable log entries that indicate that the peer is behind on its
// log. In these cases, it is likely safe to send out the rejection
// response immediately without compromising safety in the presence of a
// server restart. However, because these rejections are rare and
// because the safety of such behavior has not been formally verified,
// we err on the side of safety and omit a `&& !m.Reject` condition
// above.
r.msgsAfterAppend = append(r.msgsAfterAppend, m)
} else {
if m.To == r.id {
r.logger.Panicf("message should not be self-addressed when sending %s", m.Type)
}
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
}
lastIndex, nextIndex := pr.Next-1, pr.Next
lastTerm, errt := r.raftLog.term(lastIndex)
var ents []pb.Entry
var erre error
// In a throttled StateReplicate only send empty MsgApp, to ensure progress.
// Otherwise, if we had a full Inflights and all inflight messages were in
// fact dropped, replication to that follower would stall. Instead, an empty
// MsgApp will eventually reach the follower (heartbeats responses prompt the
// leader to send an append), allowing it to be acked or rejected, both of
// which will clear out Inflights.
if pr.State != tracker.StateReplicate || !pr.Inflights.Full() {
ents, erre = r.raftLog.entries(nextIndex, 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
}
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")
}
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)
r.send(pb.Message{To: to, Type: pb.MsgSnap, Snapshot: &snapshot})
return true
}
// Send the actual MsgApp otherwise, and update the progress accordingly.
if err := pr.UpdateOnEntriesSend(len(ents), uint64(payloadsSize(ents)), nextIndex); err != nil {
r.logger.Panicf("%x: %v", r.id, err)
}
// NB: pr has been updated, but we make sure to only use its old values below.
r.send(pb.Message{
To: to,
Type: pb.MsgApp,
Index: lastIndex,
LogTerm: lastTerm,
Entries: ents,
Commit: r.raftLog.committed,
})
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) appliedTo(index uint64, size entryEncodingSize) {
oldApplied := r.raftLog.applied
newApplied := max(index, oldApplied)
r.raftLog.appliedTo(newApplied, size)
if r.prs.Config.AutoLeave && newApplied >= 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. We use a
// nil Data which unmarshals into an empty ConfChangeV2 and has the
// benefit that appendEntry can never refuse it based on its size
// (which registers as zero).
m, err := confChangeToMsg(nil)
if err != nil {
panic(err)
}
// NB: this proposal can't be dropped due to size, but can be
// dropped if a leadership transfer is in progress. We'll keep
// checking this condition on each applied entry, so either the
// leadership transfer will succeed and the new leader will leave
// the joint configuration, or the leadership transfer will fail,
// and we will propose the config change on the next advance.
if err := r.Step(m); err != nil {
r.logger.Debugf("not initiating automatic transition out of joint configuration %s: %v", r.prs.Config, err)
} else {
r.logger.Infof("initiating automatic transition out of joint configuration %s", r.prs.Config)
}
}
}
func (r *raft) appliedSnap(snap *pb.Snapshot) {
index := snap.Metadata.Index
r.raftLog.stableSnapTo(index)
r.appliedTo(index, 0 /* size */)
}
// 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, r.prs.MaxInflightBytes),
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.Warningf(
"%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...)
// The leader needs to self-ack the entries just appended once they have
// been durably persisted (since it doesn't send an MsgApp to itself). This
// response message will be added to msgsAfterAppend and delivered back to
// this node after these entries have been written to stable storage. When
// handled, this is roughly equivalent to:
//
// r.prs.Progress[r.id].MaybeUpdate(e.Index)
// if r.maybeCommit() {
// r.bcastAppend()
// }
r.send(pb.Message{To: r.id, Type: pb.MsgAppResp, Index: li})
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
if err := r.Step(pb.Message{From: r.id, Type: pb.MsgHup}); err != nil {
r.logger.Debugf("error occurred during election: %v", err)
}
}
}
// 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 {
if err := r.Step(pb.Message{From: r.id, Type: pb.MsgCheckQuorum}); err != nil {
r.logger.Debugf("error occurred during checking sending heartbeat: %v", err)
}
}
// 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
if err := r.Step(pb.Message{From: r.id, Type: pb.MsgBeat}); err != nil {
r.logger.Debugf("error occurred during checking sending heartbeat: %v", err)
}
}
}
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.
pr := r.prs.Progress[r.id]
pr.BecomeReplicate()
// The leader always has RecentActive == true; MsgCheckQuorum makes sure to
// preserve this.
pr.RecentActive = true
// 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")
}
// The payloadSize of an empty entry is 0 (see TestPayloadSizeOfEmptyEntry),
// so the preceding log append does not count against the uncommitted log
// quota of the new leader. In other words, after the call to appendEntry,
// r.uncommittedSize is still 0.
r.logger.Infof("%x became leader at term %d", r.id, r.Term)
}
func (r *raft) hup(t CampaignType) {
if r.state == StateLeader {
r.logger.Debugf("%x ignoring MsgHup because already leader", r.id)
return
}
if !r.promotable() {
r.logger.Warningf("%x is unpromotable and can not campaign", r.id)
return
}
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
}
r.logger.Infof("%x is starting a new election at term %d", r.id, r.Term)
r.campaign(t)
}
// 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
}
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 {
// The candidate votes for itself and should account for this self
// vote once the vote has been durably persisted (since it doesn't
// send a MsgVote to itself). This response message will be added to
// msgsAfterAppend and delivered back to this node after the vote
// has been written to stable storage.
r.send(pb.Message{To: id, Term: term, Type: voteRespMsgType(voteMsg)})
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{To: id, Term: term, 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