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// Copyright 2019 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 tracker
import (
"fmt"
"sort"
"strings"
"go.etcd.io/etcd/raft/quorum"
pb "go.etcd.io/etcd/raft/raftpb"
)
// Config reflects the configuration tracked in a ProgressTracker.
type Config struct {
Voters quorum.JointConfig
// AutoLeave is true if the configuration is joint and a transition to the
// incoming configuration should be carried out automatically by Raft when
// this is possible. If false, the configuration will be joint until the
// application initiates the transition manually.
AutoLeave bool
// Learners is a set of IDs corresponding to the learners active in the
// current configuration.
//
// Invariant: Learners and Voters does not intersect, i.e. if a peer is in
// either half of the joint config, it can't be a learner; if it is a
// learner it can't be in either half of the joint config. This invariant
// simplifies the implementation since it allows peers to have clarity about
// its current role without taking into account joint consensus.
Learners map[uint64]struct{}
// When we turn a voter into a learner during a joint consensus transition,
// we cannot add the learner directly when entering the joint state. This is
// because this would violate the invariant that the intersection of
// voters and learners is empty. For example, assume a Voter is removed and
// immediately re-added as a learner (or in other words, it is demoted):
//
// Initially, the configuration will be
//
// voters: {1 2 3}
// learners: {}
//
// and we want to demote 3. Entering the joint configuration, we naively get
//
// voters: {1 2} & {1 2 3}
// learners: {3}
//
// but this violates the invariant (3 is both voter and learner). Instead,
// we get
//
// voters: {1 2} & {1 2 3}
// learners: {}
// next_learners: {3}
//
// Where 3 is now still purely a voter, but we are remembering the intention
// to make it a learner upon transitioning into the final configuration:
//
// voters: {1 2}
// learners: {3}
// next_learners: {}
//
// Note that next_learners is not used while adding a learner that is not
// also a voter in the joint config. In this case, the learner is added
// right away when entering the joint configuration, so that it is caught up
// as soon as possible.
LearnersNext map[uint64]struct{}
}
func (c Config) String() string {
var buf strings.Builder
fmt.Fprintf(&buf, "voters=%s", c.Voters)
if c.Learners != nil {
fmt.Fprintf(&buf, " learners=%s", quorum.MajorityConfig(c.Learners).String())
}
if c.LearnersNext != nil {
fmt.Fprintf(&buf, " learners_next=%s", quorum.MajorityConfig(c.LearnersNext).String())
}
if c.AutoLeave {
fmt.Fprintf(&buf, " autoleave")
}
return buf.String()
}
// Clone returns a copy of the Config that shares no memory with the original.
func (c *Config) Clone() Config {
clone := func(m map[uint64]struct{}) map[uint64]struct{} {
if m == nil {
return nil
}
mm := make(map[uint64]struct{}, len(m))
for k := range m {
mm[k] = struct{}{}
}
return mm
}
return Config{
Voters: quorum.JointConfig{clone(c.Voters[0]), clone(c.Voters[1])},
Learners: clone(c.Learners),
LearnersNext: clone(c.LearnersNext),
}
}
// ProgressTracker tracks the currently active configuration and the information
// known about the nodes and learners in it. In particular, it tracks the match
// index for each peer which in turn allows reasoning about the committed index.
type ProgressTracker struct {
Config
Progress ProgressMap
Votes map[uint64]bool
MaxInflight int
}
// MakeProgressTracker initializes a ProgressTracker.
func MakeProgressTracker(maxInflight int) ProgressTracker {
p := ProgressTracker{
MaxInflight: maxInflight,
Config: Config{
Voters: quorum.JointConfig{
quorum.MajorityConfig{},
nil, // only populated when used
},
Learners: nil, // only populated when used
LearnersNext: nil, // only populated when used
},
Votes: map[uint64]bool{},
Progress: map[uint64]*Progress{},
}
return p
}
// ConfState returns a ConfState representing the active configuration.
func (p *ProgressTracker) ConfState() pb.ConfState {
return pb.ConfState{
Voters: p.Voters[0].Slice(),
VotersOutgoing: p.Voters[1].Slice(),
Learners: quorum.MajorityConfig(p.Learners).Slice(),
LearnersNext: quorum.MajorityConfig(p.LearnersNext).Slice(),
AutoLeave: p.AutoLeave,
}
}
// IsSingleton returns true if (and only if) there is only one voting member
// (i.e. the leader) in the current configuration.
func (p *ProgressTracker) IsSingleton() bool {
return len(p.Voters[0]) == 1 && len(p.Voters[1]) == 0
}
type matchAckIndexer map[uint64]*Progress
var _ quorum.AckedIndexer = matchAckIndexer(nil)
// AckedIndex implements IndexLookuper.
func (l matchAckIndexer) AckedIndex(id uint64) (quorum.Index, bool) {
pr, ok := l[id]
if !ok {
return 0, false
}
return quorum.Index(pr.Match), true
}
// Committed returns the largest log index known to be committed based on what
// the voting members of the group have acknowledged.
func (p *ProgressTracker) Committed() uint64 {
return uint64(p.Voters.CommittedIndex(matchAckIndexer(p.Progress)))
}
func insertionSort(sl []uint64) {
a, b := 0, len(sl)
for i := a + 1; i < b; i++ {
for j := i; j > a && sl[j] < sl[j-1]; j-- {
sl[j], sl[j-1] = sl[j-1], sl[j]
}
}
}
// Visit invokes the supplied closure for all tracked progresses in stable order.
func (p *ProgressTracker) Visit(f func(id uint64, pr *Progress)) {
n := len(p.Progress)
// We need to sort the IDs and don't want to allocate since this is hot code.
// The optimization here mirrors that in `(MajorityConfig).CommittedIndex`,
// see there for details.
var sl [7]uint64
ids := sl[:]
if len(sl) >= n {
ids = sl[:n]
} else {
ids = make([]uint64, n)
}
for id := range p.Progress {
n--
ids[n] = id
}
insertionSort(ids)
for _, id := range ids {
f(id, p.Progress[id])
}
}
// QuorumActive returns true if the quorum is active from the view of the local
// raft state machine. Otherwise, it returns false.
func (p *ProgressTracker) QuorumActive() bool {
votes := map[uint64]bool{}
p.Visit(func(id uint64, pr *Progress) {
if pr.IsLearner {
return
}
votes[id] = pr.RecentActive
})
return p.Voters.VoteResult(votes) == quorum.VoteWon
}
// VoterNodes returns a sorted slice of voters.
func (p *ProgressTracker) VoterNodes() []uint64 {
m := p.Voters.IDs()
nodes := make([]uint64, 0, len(m))
for id := range m {
nodes = append(nodes, id)
}
sort.Slice(nodes, func(i, j int) bool { return nodes[i] < nodes[j] })
return nodes
}
// LearnerNodes returns a sorted slice of learners.
func (p *ProgressTracker) LearnerNodes() []uint64 {
if len(p.Learners) == 0 {
return nil
}
nodes := make([]uint64, 0, len(p.Learners))
for id := range p.Learners {
nodes = append(nodes, id)
}
sort.Slice(nodes, func(i, j int) bool { return nodes[i] < nodes[j] })
return nodes
}
// ResetVotes prepares for a new round of vote counting via recordVote.
func (p *ProgressTracker) ResetVotes() {
p.Votes = map[uint64]bool{}
}
// RecordVote records that the node with the given id voted for this Raft
// instance if v == true (and declined it otherwise).
func (p *ProgressTracker) RecordVote(id uint64, v bool) {
_, ok := p.Votes[id]
if !ok {
p.Votes[id] = v
}
}
// TallyVotes returns the number of granted and rejected Votes, and whether the
// election outcome is known.
func (p *ProgressTracker) TallyVotes() (granted int, rejected int, _ quorum.VoteResult) {
// Make sure to populate granted/rejected correctly even if the Votes slice
// contains members no longer part of the configuration. This doesn't really
// matter in the way the numbers are used (they're informational), but might
// as well get it right.
for id, pr := range p.Progress {
if pr.IsLearner {
continue
}
v, voted := p.Votes[id]
if !voted {
continue
}
if v {
granted++
} else {
rejected++
}
}
result := p.Voters.VoteResult(p.Votes)
return granted, rejected, result
}