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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 "fmt"
const (
ProgressStateProbe ProgressStateType = iota
ProgressStateReplicate
ProgressStateSnapshot
)
type ProgressStateType uint64
var prstmap = [...]string{
"ProgressStateProbe",
"ProgressStateReplicate",
"ProgressStateSnapshot",
}
func (st ProgressStateType) String() string { return prstmap[uint64(st)] }
// Progress represents a follower’s progress in the view of the leader. Leader maintains
// progresses of all followers, and sends entries to the follower based on its progress.
type Progress struct {
Match, Next uint64
// State defines how the leader should interact with the follower.
//
// When in ProgressStateProbe, leader sends at most one replication message
// per heartbeat interval. It also probes actual progress of the follower.
//
// When in ProgressStateReplicate, leader optimistically increases next
// to the latest entry sent after sending replication message. This is
// an optimized state for fast replicating log entries to the follower.
//
// When in ProgressStateSnapshot, leader should have sent out snapshot
// before and stops sending any replication message.
State ProgressStateType
// Paused is used in ProgressStateProbe.
// When Paused is true, raft should pause sending replication message to this peer.
Paused bool
// PendingSnapshot is used in ProgressStateSnapshot.
// If there is a pending snapshot, the pendingSnapshot will be set to the
// index of the snapshot. If pendingSnapshot is set, the replication process of
// this Progress will be paused. raft will not resend snapshot until the pending one
// is reported to be failed.
PendingSnapshot uint64
// RecentActive is true if the progress is recently active. Receiving any messages
// from the corresponding follower indicates the progress is active.
// RecentActive can be reset to false after an election timeout.
RecentActive bool
// inflights is a sliding window for the inflight messages.
// Each inflight message contains one or more log entries.
// The max number of entries per message is defined in raft config as MaxSizePerMsg.
// Thus inflight effectively limits both the number of inflight messages
// and the bandwidth each Progress can use.
// When inflights is full, no more message should be sent.
// When a leader sends out a message, the index of the last
// entry should be added to inflights. The index MUST be added
// into inflights in order.
// When a leader receives a reply, the previous inflights should
// be freed by calling inflights.freeTo with the index of the last
// received entry.
ins *inflights
// IsLearner is true if this progress is tracked for a learner.
IsLearner bool
}
func (pr *Progress) resetState(state ProgressStateType) {
pr.Paused = false
pr.PendingSnapshot = 0
pr.State = state
pr.ins.reset()
}
func (pr *Progress) becomeProbe() {
// If the original state is ProgressStateSnapshot, progress knows that
// the pending snapshot has been sent to this peer successfully, then
// probes from pendingSnapshot + 1.
if pr.State == ProgressStateSnapshot {
pendingSnapshot := pr.PendingSnapshot
pr.resetState(ProgressStateProbe)
pr.Next = max(pr.Match+1, pendingSnapshot+1)
} else {
pr.resetState(ProgressStateProbe)
pr.Next = pr.Match + 1
}
}
func (pr *Progress) becomeReplicate() {
pr.resetState(ProgressStateReplicate)
pr.Next = pr.Match + 1
}
func (pr *Progress) becomeSnapshot(snapshoti uint64) {
pr.resetState(ProgressStateSnapshot)
pr.PendingSnapshot = snapshoti
}
// maybeUpdate returns false if the given n index comes from an outdated message.
// Otherwise it updates the progress and returns true.
func (pr *Progress) maybeUpdate(n uint64) bool {
var updated bool
if pr.Match < n {
pr.Match = n
updated = true
pr.resume()
}
if pr.Next < n+1 {
pr.Next = n + 1
}
return updated
}
func (pr *Progress) optimisticUpdate(n uint64) { pr.Next = n + 1 }
// maybeDecrTo returns false if the given to index comes from an out of order message.
// Otherwise it decreases the progress next index to min(rejected, last) and returns true.
func (pr *Progress) maybeDecrTo(rejected, last uint64) bool {
if pr.State == ProgressStateReplicate {
// the rejection must be stale if the progress has matched and "rejected"
// is smaller than "match".
if rejected <= pr.Match {
return false
}
// directly decrease next to match + 1
pr.Next = pr.Match + 1
return true
}
// the rejection must be stale if "rejected" does not match next - 1
if pr.Next-1 != rejected {
return false
}
if pr.Next = min(rejected, last+1); pr.Next < 1 {
pr.Next = 1
}
pr.resume()
return true
}
func (pr *Progress) pause() { pr.Paused = true }
func (pr *Progress) resume() { pr.Paused = false }
// IsPaused returns whether sending log entries to this node has been
// paused. A node may be paused because it has rejected recent
// MsgApps, is currently waiting for a snapshot, or has reached the
// MaxInflightMsgs limit.
func (pr *Progress) IsPaused() bool {
switch pr.State {
case ProgressStateProbe:
return pr.Paused
case ProgressStateReplicate:
return pr.ins.full()
case ProgressStateSnapshot:
return true
default:
panic("unexpected state")
}
}
func (pr *Progress) snapshotFailure() { pr.PendingSnapshot = 0 }
// needSnapshotAbort returns true if snapshot progress's Match
// is equal or higher than the pendingSnapshot.
func (pr *Progress) needSnapshotAbort() bool {
return pr.State == ProgressStateSnapshot && pr.Match >= pr.PendingSnapshot
}
func (pr *Progress) String() string {
return fmt.Sprintf("next = %d, match = %d, state = %s, waiting = %v, pendingSnapshot = %d", pr.Next, pr.Match, pr.State, pr.IsPaused(), pr.PendingSnapshot)
}
type inflights struct {
// the starting index in the buffer
start int
// number of inflights in the buffer
count int
// the size of the buffer
size int
// buffer contains the index of the last entry
// inside one message.
buffer []uint64
}
func newInflights(size int) *inflights {
return &inflights{
size: size,
}
}
// add adds an inflight into inflights
func (in *inflights) add(inflight uint64) {
if in.full() {
panic("cannot add into a full inflights")
}
next := in.start + in.count
size := in.size
if next >= size {
next -= size
}
if next >= len(in.buffer) {
in.growBuf()
}
in.buffer[next] = inflight
in.count++
}
// grow the inflight buffer by doubling up to inflights.size. We grow on demand
// instead of preallocating to inflights.size to handle systems which have
// thousands of Raft groups per process.
func (in *inflights) growBuf() {
newSize := len(in.buffer) * 2
if newSize == 0 {
newSize = 1
} else if newSize > in.size {
newSize = in.size
}
newBuffer := make([]uint64, newSize)
copy(newBuffer, in.buffer)
in.buffer = newBuffer
}
// freeTo frees the inflights smaller or equal to the given `to` flight.
func (in *inflights) freeTo(to uint64) {
if in.count == 0 || to < in.buffer[in.start] {
// out of the left side of the window
return
}
idx := in.start
var i int
for i = 0; i < in.count; i++ {
if to < in.buffer[idx] { // found the first large inflight
break
}
// increase index and maybe rotate
size := in.size
if idx++; idx >= size {
idx -= size
}
}
// free i inflights and set new start index
in.count -= i
in.start = idx
if in.count == 0 {
// inflights is empty, reset the start index so that we don't grow the
// buffer unnecessarily.
in.start = 0
}
}
func (in *inflights) freeFirstOne() { in.freeTo(in.buffer[in.start]) }
// full returns true if the inflights is full.
func (in *inflights) full() bool {
return in.count == in.size
}
// resets frees all inflights.
func (in *inflights) reset() {
in.count = 0
in.start = 0
}