forked from mystiq/dex
288 lines
8.5 KiB
Go
288 lines
8.5 KiB
Go
// Copyright 2019 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package tracker
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import (
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"fmt"
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"sort"
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"strings"
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"go.etcd.io/etcd/raft/quorum"
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pb "go.etcd.io/etcd/raft/raftpb"
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)
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// Config reflects the configuration tracked in a ProgressTracker.
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type Config struct {
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Voters quorum.JointConfig
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// AutoLeave is true if the configuration is joint and a transition to the
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// incoming configuration should be carried out automatically by Raft when
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// this is possible. If false, the configuration will be joint until the
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// application initiates the transition manually.
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AutoLeave bool
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// Learners is a set of IDs corresponding to the learners active in the
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// current configuration.
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//
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// Invariant: Learners and Voters does not intersect, i.e. if a peer is in
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// either half of the joint config, it can't be a learner; if it is a
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// learner it can't be in either half of the joint config. This invariant
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// simplifies the implementation since it allows peers to have clarity about
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// its current role without taking into account joint consensus.
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Learners map[uint64]struct{}
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// When we turn a voter into a learner during a joint consensus transition,
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// we cannot add the learner directly when entering the joint state. This is
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// because this would violate the invariant that the intersection of
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// voters and learners is empty. For example, assume a Voter is removed and
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// immediately re-added as a learner (or in other words, it is demoted):
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//
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// Initially, the configuration will be
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//
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// voters: {1 2 3}
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// learners: {}
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//
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// and we want to demote 3. Entering the joint configuration, we naively get
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//
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// voters: {1 2} & {1 2 3}
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// learners: {3}
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//
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// but this violates the invariant (3 is both voter and learner). Instead,
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// we get
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//
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// voters: {1 2} & {1 2 3}
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// learners: {}
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// next_learners: {3}
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//
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// Where 3 is now still purely a voter, but we are remembering the intention
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// to make it a learner upon transitioning into the final configuration:
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//
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// voters: {1 2}
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// learners: {3}
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// next_learners: {}
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//
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// Note that next_learners is not used while adding a learner that is not
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// also a voter in the joint config. In this case, the learner is added
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// right away when entering the joint configuration, so that it is caught up
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// as soon as possible.
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LearnersNext map[uint64]struct{}
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}
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func (c Config) String() string {
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var buf strings.Builder
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fmt.Fprintf(&buf, "voters=%s", c.Voters)
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if c.Learners != nil {
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fmt.Fprintf(&buf, " learners=%s", quorum.MajorityConfig(c.Learners).String())
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}
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if c.LearnersNext != nil {
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fmt.Fprintf(&buf, " learners_next=%s", quorum.MajorityConfig(c.LearnersNext).String())
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}
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if c.AutoLeave {
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fmt.Fprintf(&buf, " autoleave")
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}
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return buf.String()
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}
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// Clone returns a copy of the Config that shares no memory with the original.
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func (c *Config) Clone() Config {
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clone := func(m map[uint64]struct{}) map[uint64]struct{} {
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if m == nil {
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return nil
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}
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mm := make(map[uint64]struct{}, len(m))
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for k := range m {
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mm[k] = struct{}{}
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}
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return mm
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}
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return Config{
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Voters: quorum.JointConfig{clone(c.Voters[0]), clone(c.Voters[1])},
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Learners: clone(c.Learners),
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LearnersNext: clone(c.LearnersNext),
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}
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}
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// ProgressTracker tracks the currently active configuration and the information
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// known about the nodes and learners in it. In particular, it tracks the match
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// index for each peer which in turn allows reasoning about the committed index.
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type ProgressTracker struct {
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Config
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Progress ProgressMap
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Votes map[uint64]bool
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MaxInflight int
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}
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// MakeProgressTracker initializes a ProgressTracker.
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func MakeProgressTracker(maxInflight int) ProgressTracker {
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p := ProgressTracker{
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MaxInflight: maxInflight,
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Config: Config{
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Voters: quorum.JointConfig{
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quorum.MajorityConfig{},
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nil, // only populated when used
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},
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Learners: nil, // only populated when used
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LearnersNext: nil, // only populated when used
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},
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Votes: map[uint64]bool{},
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Progress: map[uint64]*Progress{},
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}
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return p
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}
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// ConfState returns a ConfState representing the active configuration.
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func (p *ProgressTracker) ConfState() pb.ConfState {
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return pb.ConfState{
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Voters: p.Voters[0].Slice(),
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VotersOutgoing: p.Voters[1].Slice(),
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Learners: quorum.MajorityConfig(p.Learners).Slice(),
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LearnersNext: quorum.MajorityConfig(p.LearnersNext).Slice(),
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AutoLeave: p.AutoLeave,
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}
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}
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// IsSingleton returns true if (and only if) there is only one voting member
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// (i.e. the leader) in the current configuration.
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func (p *ProgressTracker) IsSingleton() bool {
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return len(p.Voters[0]) == 1 && len(p.Voters[1]) == 0
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}
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type matchAckIndexer map[uint64]*Progress
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var _ quorum.AckedIndexer = matchAckIndexer(nil)
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// AckedIndex implements IndexLookuper.
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func (l matchAckIndexer) AckedIndex(id uint64) (quorum.Index, bool) {
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pr, ok := l[id]
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if !ok {
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return 0, false
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}
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return quorum.Index(pr.Match), true
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}
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// Committed returns the largest log index known to be committed based on what
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// the voting members of the group have acknowledged.
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func (p *ProgressTracker) Committed() uint64 {
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return uint64(p.Voters.CommittedIndex(matchAckIndexer(p.Progress)))
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}
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func insertionSort(sl []uint64) {
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a, b := 0, len(sl)
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for i := a + 1; i < b; i++ {
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for j := i; j > a && sl[j] < sl[j-1]; j-- {
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sl[j], sl[j-1] = sl[j-1], sl[j]
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}
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}
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}
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// Visit invokes the supplied closure for all tracked progresses in stable order.
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func (p *ProgressTracker) Visit(f func(id uint64, pr *Progress)) {
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n := len(p.Progress)
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// We need to sort the IDs and don't want to allocate since this is hot code.
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// The optimization here mirrors that in `(MajorityConfig).CommittedIndex`,
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// see there for details.
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var sl [7]uint64
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ids := sl[:]
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if len(sl) >= n {
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ids = sl[:n]
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} else {
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ids = make([]uint64, n)
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}
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for id := range p.Progress {
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n--
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ids[n] = id
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}
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insertionSort(ids)
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for _, id := range ids {
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f(id, p.Progress[id])
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}
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}
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// QuorumActive returns true if the quorum is active from the view of the local
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// raft state machine. Otherwise, it returns false.
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func (p *ProgressTracker) QuorumActive() bool {
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votes := map[uint64]bool{}
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p.Visit(func(id uint64, pr *Progress) {
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if pr.IsLearner {
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return
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}
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votes[id] = pr.RecentActive
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})
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return p.Voters.VoteResult(votes) == quorum.VoteWon
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}
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// VoterNodes returns a sorted slice of voters.
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func (p *ProgressTracker) VoterNodes() []uint64 {
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m := p.Voters.IDs()
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nodes := make([]uint64, 0, len(m))
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for id := range m {
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nodes = append(nodes, id)
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}
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sort.Slice(nodes, func(i, j int) bool { return nodes[i] < nodes[j] })
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return nodes
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}
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// LearnerNodes returns a sorted slice of learners.
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func (p *ProgressTracker) LearnerNodes() []uint64 {
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if len(p.Learners) == 0 {
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return nil
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}
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nodes := make([]uint64, 0, len(p.Learners))
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for id := range p.Learners {
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nodes = append(nodes, id)
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}
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sort.Slice(nodes, func(i, j int) bool { return nodes[i] < nodes[j] })
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return nodes
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}
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// ResetVotes prepares for a new round of vote counting via recordVote.
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func (p *ProgressTracker) ResetVotes() {
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p.Votes = map[uint64]bool{}
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}
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// RecordVote records that the node with the given id voted for this Raft
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// instance if v == true (and declined it otherwise).
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func (p *ProgressTracker) RecordVote(id uint64, v bool) {
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_, ok := p.Votes[id]
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if !ok {
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p.Votes[id] = v
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}
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}
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// TallyVotes returns the number of granted and rejected Votes, and whether the
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// election outcome is known.
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func (p *ProgressTracker) TallyVotes() (granted int, rejected int, _ quorum.VoteResult) {
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// Make sure to populate granted/rejected correctly even if the Votes slice
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// contains members no longer part of the configuration. This doesn't really
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// matter in the way the numbers are used (they're informational), but might
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// as well get it right.
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for id, pr := range p.Progress {
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if pr.IsLearner {
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continue
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}
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v, voted := p.Votes[id]
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if !voted {
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continue
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}
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if v {
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granted++
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} else {
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rejected++
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}
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}
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result := p.Voters.VoteResult(p.Votes)
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return granted, rejected, result
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}
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