/usr/share/gocode/src/github.com/hashicorp/raft/replication.go is in golang-github-hashicorp-raft-dev 0.0~git20150728.9b586e2-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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import (
"errors"
"fmt"
"sync"
"time"
"github.com/armon/go-metrics"
)
const (
maxFailureScale = 12
failureWait = 10 * time.Millisecond
)
var (
// ErrLogNotFound indicates a given log entry is not available.
ErrLogNotFound = errors.New("log not found")
// ErrPipelineReplicationNotSupported can be returned by the transport to
// signal that pipeline replication is not supported in general, and that
// no error message should be produced.
ErrPipelineReplicationNotSupported = errors.New("pipeline replication not supported")
)
type followerReplication struct {
peer string
inflight *inflight
stopCh chan uint64
triggerCh chan struct{}
currentTerm uint64
matchIndex uint64
nextIndex uint64
lastContact time.Time
lastContactLock sync.RWMutex
failures uint64
notifyCh chan struct{}
notify []*verifyFuture
notifyLock sync.Mutex
// stepDown is used to indicate to the leader that we
// should step down based on information from a follower.
stepDown chan struct{}
// allowPipeline is used to control it seems like
// pipeline replication should be enabled.
allowPipeline bool
}
// notifyAll is used to notify all the waiting verify futures
// if the follower believes we are still the leader.
func (s *followerReplication) notifyAll(leader bool) {
// Clear the waiting notifies minimizing lock time
s.notifyLock.Lock()
n := s.notify
s.notify = nil
s.notifyLock.Unlock()
// Submit our votes
for _, v := range n {
v.vote(leader)
}
}
// LastContact returns the time of last contact.
func (s *followerReplication) LastContact() time.Time {
s.lastContactLock.RLock()
last := s.lastContact
s.lastContactLock.RUnlock()
return last
}
// setLastContact sets the last contact to the current time.
func (s *followerReplication) setLastContact() {
s.lastContactLock.Lock()
s.lastContact = time.Now()
s.lastContactLock.Unlock()
}
// replicate is a long running routine that is used to manage
// the process of replicating logs to our followers.
func (r *Raft) replicate(s *followerReplication) {
// Start an async heartbeating routing
stopHeartbeat := make(chan struct{})
defer close(stopHeartbeat)
r.goFunc(func() { r.heartbeat(s, stopHeartbeat) })
RPC:
shouldStop := false
for !shouldStop {
select {
case maxIndex := <-s.stopCh:
// Make a best effort to replicate up to this index
if maxIndex > 0 {
r.replicateTo(s, maxIndex)
}
return
case <-s.triggerCh:
shouldStop = r.replicateTo(s, r.getLastLogIndex())
case <-randomTimeout(r.conf.CommitTimeout):
shouldStop = r.replicateTo(s, r.getLastLogIndex())
}
// If things looks healthy, switch to pipeline mode
if !shouldStop && s.allowPipeline {
goto PIPELINE
}
}
return
PIPELINE:
// Disable until re-enabled
s.allowPipeline = false
// Replicates using a pipeline for high performance. This method
// is not able to gracefully recover from errors, and so we fall back
// to standard mode on failure.
if err := r.pipelineReplicate(s); err != nil {
if err != ErrPipelineReplicationNotSupported {
r.logger.Printf("[ERR] raft: Failed to start pipeline replication to %s: %s", s.peer, err)
}
}
goto RPC
}
// replicateTo is used to replicate the logs up to a given last index.
// If the follower log is behind, we take care to bring them up to date.
func (r *Raft) replicateTo(s *followerReplication, lastIndex uint64) (shouldStop bool) {
// Create the base request
var req AppendEntriesRequest
var resp AppendEntriesResponse
var start time.Time
START:
// Prevent an excessive retry rate on errors
if s.failures > 0 {
select {
case <-time.After(backoff(failureWait, s.failures, maxFailureScale)):
case <-r.shutdownCh:
}
}
// Setup the request
if err := r.setupAppendEntries(s, &req, s.nextIndex, lastIndex); err == ErrLogNotFound {
goto SEND_SNAP
} else if err != nil {
return
}
// Make the RPC call
start = time.Now()
if err := r.trans.AppendEntries(s.peer, &req, &resp); err != nil {
r.logger.Printf("[ERR] raft: Failed to AppendEntries to %v: %v", s.peer, err)
s.failures++
return
}
appendStats(s.peer, start, float32(len(req.Entries)))
// Check for a newer term, stop running
if resp.Term > req.Term {
r.handleStaleTerm(s)
return true
}
// Update the last contact
s.setLastContact()
// Update s based on success
if resp.Success {
// Update our replication state
updateLastAppended(s, &req)
// Clear any failures, allow pipelining
s.failures = 0
s.allowPipeline = true
} else {
s.nextIndex = max(min(s.nextIndex-1, resp.LastLog+1), 1)
s.matchIndex = s.nextIndex - 1
s.failures++
r.logger.Printf("[WARN] raft: AppendEntries to %v rejected, sending older logs (next: %d)", s.peer, s.nextIndex)
}
CHECK_MORE:
// Check if there are more logs to replicate
if s.nextIndex <= lastIndex {
goto START
}
return
// SEND_SNAP is used when we fail to get a log, usually because the follower
// is too far behind, and we must ship a snapshot down instead
SEND_SNAP:
if stop, err := r.sendLatestSnapshot(s); stop {
return true
} else if err != nil {
r.logger.Printf("[ERR] raft: Failed to send snapshot to %v: %v", s.peer, err)
return
}
// Check if there is more to replicate
goto CHECK_MORE
}
// sendLatestSnapshot is used to send the latest snapshot we have
// down to our follower.
func (r *Raft) sendLatestSnapshot(s *followerReplication) (bool, error) {
// Get the snapshots
snapshots, err := r.snapshots.List()
if err != nil {
r.logger.Printf("[ERR] raft: Failed to list snapshots: %v", err)
return false, err
}
// Check we have at least a single snapshot
if len(snapshots) == 0 {
return false, fmt.Errorf("no snapshots found")
}
// Open the most recent snapshot
snapID := snapshots[0].ID
meta, snapshot, err := r.snapshots.Open(snapID)
if err != nil {
r.logger.Printf("[ERR] raft: Failed to open snapshot %v: %v", snapID, err)
return false, err
}
defer snapshot.Close()
// Setup the request
req := InstallSnapshotRequest{
Term: s.currentTerm,
Leader: r.trans.EncodePeer(r.localAddr),
LastLogIndex: meta.Index,
LastLogTerm: meta.Term,
Peers: meta.Peers,
Size: meta.Size,
}
// Make the call
start := time.Now()
var resp InstallSnapshotResponse
if err := r.trans.InstallSnapshot(s.peer, &req, &resp, snapshot); err != nil {
r.logger.Printf("[ERR] raft: Failed to install snapshot %v: %v", snapID, err)
s.failures++
return false, err
}
metrics.MeasureSince([]string{"raft", "replication", "installSnapshot", s.peer}, start)
// Check for a newer term, stop running
if resp.Term > req.Term {
r.handleStaleTerm(s)
return true, nil
}
// Update the last contact
s.setLastContact()
// Check for success
if resp.Success {
// Mark any inflight logs as committed
s.inflight.CommitRange(s.matchIndex+1, meta.Index)
// Update the indexes
s.matchIndex = meta.Index
s.nextIndex = s.matchIndex + 1
// Clear any failures
s.failures = 0
// Notify we are still leader
s.notifyAll(true)
} else {
s.failures++
r.logger.Printf("[WARN] raft: InstallSnapshot to %v rejected", s.peer)
}
return false, nil
}
// heartbeat is used to periodically invoke AppendEntries on a peer
// to ensure they don't time out. This is done async of replicate(),
// since that routine could potentially be blocked on disk IO.
func (r *Raft) heartbeat(s *followerReplication, stopCh chan struct{}) {
var failures uint64
req := AppendEntriesRequest{
Term: s.currentTerm,
Leader: r.trans.EncodePeer(r.localAddr),
}
var resp AppendEntriesResponse
for {
// Wait for the next heartbeat interval or forced notify
select {
case <-s.notifyCh:
case <-randomTimeout(r.conf.HeartbeatTimeout / 10):
case <-stopCh:
return
}
start := time.Now()
if err := r.trans.AppendEntries(s.peer, &req, &resp); err != nil {
r.logger.Printf("[ERR] raft: Failed to heartbeat to %v: %v", s.peer, err)
failures++
select {
case <-time.After(backoff(failureWait, failures, maxFailureScale)):
case <-stopCh:
}
} else {
s.setLastContact()
failures = 0
metrics.MeasureSince([]string{"raft", "replication", "heartbeat", s.peer}, start)
s.notifyAll(resp.Success)
}
}
}
// pipelineReplicate is used when we have synchronized our state with the follower,
// and want to switch to a higher performance pipeline mode of replication.
// We only pipeline AppendEntries commands, and if we ever hit an error, we fall
// back to the standard replication which can handle more complex situations.
func (r *Raft) pipelineReplicate(s *followerReplication) error {
// Create a new pipeline
pipeline, err := r.trans.AppendEntriesPipeline(s.peer)
if err != nil {
return err
}
defer pipeline.Close()
// Log start and stop of pipeline
r.logger.Printf("[INFO] raft: pipelining replication to peer %v", s.peer)
defer r.logger.Printf("[INFO] raft: aborting pipeline replication to peer %v", s.peer)
// Create a shutdown and finish channel
stopCh := make(chan struct{})
finishCh := make(chan struct{})
// Start a dedicated decoder
r.goFunc(func() { r.pipelineDecode(s, pipeline, stopCh, finishCh) })
// Start pipeline sends at the last good nextIndex
nextIndex := s.nextIndex
shouldStop := false
SEND:
for !shouldStop {
select {
case <-finishCh:
break SEND
case maxIndex := <-s.stopCh:
if maxIndex > 0 {
r.pipelineSend(s, pipeline, &nextIndex, maxIndex)
}
break SEND
case <-s.triggerCh:
shouldStop = r.pipelineSend(s, pipeline, &nextIndex, r.getLastLogIndex())
case <-randomTimeout(r.conf.CommitTimeout):
shouldStop = r.pipelineSend(s, pipeline, &nextIndex, r.getLastLogIndex())
}
}
// Stop our decoder, and wait for it to finish
close(stopCh)
select {
case <-finishCh:
case <-r.shutdownCh:
}
return nil
}
// pipelineSend is used to send data over a pipeline.
func (r *Raft) pipelineSend(s *followerReplication, p AppendPipeline, nextIdx *uint64, lastIndex uint64) (shouldStop bool) {
// Create a new append request
req := new(AppendEntriesRequest)
if err := r.setupAppendEntries(s, req, *nextIdx, lastIndex); err != nil {
return true
}
// Pipeline the append entries
if _, err := p.AppendEntries(req, new(AppendEntriesResponse)); err != nil {
r.logger.Printf("[ERR] raft: Failed to pipeline AppendEntries to %v: %v", s.peer, err)
return true
}
// Increase the next send log to avoid re-sending old logs
if n := len(req.Entries); n > 0 {
last := req.Entries[n-1]
*nextIdx = last.Index + 1
}
return false
}
// pipelineDecode is used to decode the responses of pipelined requests.
func (r *Raft) pipelineDecode(s *followerReplication, p AppendPipeline, stopCh, finishCh chan struct{}) {
defer close(finishCh)
respCh := p.Consumer()
for {
select {
case ready := <-respCh:
req, resp := ready.Request(), ready.Response()
appendStats(s.peer, ready.Start(), float32(len(req.Entries)))
// Check for a newer term, stop running
if resp.Term > req.Term {
r.handleStaleTerm(s)
return
}
// Update the last contact
s.setLastContact()
// Abort pipeline if not successful
if !resp.Success {
return
}
// Update our replication state
updateLastAppended(s, req)
case <-stopCh:
return
}
}
}
// setupAppendEntries is used to setup an append entries request.
func (r *Raft) setupAppendEntries(s *followerReplication, req *AppendEntriesRequest, nextIndex, lastIndex uint64) error {
req.Term = s.currentTerm
req.Leader = r.trans.EncodePeer(r.localAddr)
req.LeaderCommitIndex = r.getCommitIndex()
if err := r.setPreviousLog(req, nextIndex); err != nil {
return err
}
if err := r.setNewLogs(req, nextIndex, lastIndex); err != nil {
return err
}
return nil
}
// setPreviousLog is used to setup the PrevLogEntry and PrevLogTerm for an
// AppendEntriesRequest given the next index to replicate.
func (r *Raft) setPreviousLog(req *AppendEntriesRequest, nextIndex uint64) error {
// Guard for the first index, since there is no 0 log entry
// Guard against the previous index being a snapshot as well
if nextIndex == 1 {
req.PrevLogEntry = 0
req.PrevLogTerm = 0
} else if (nextIndex - 1) == r.getLastSnapshotIndex() {
req.PrevLogEntry = r.getLastSnapshotIndex()
req.PrevLogTerm = r.getLastSnapshotTerm()
} else {
var l Log
if err := r.logs.GetLog(nextIndex-1, &l); err != nil {
r.logger.Printf("[ERR] raft: Failed to get log at index %d: %v",
nextIndex-1, err)
return err
}
// Set the previous index and term (0 if nextIndex is 1)
req.PrevLogEntry = l.Index
req.PrevLogTerm = l.Term
}
return nil
}
// setNewLogs is used to setup the logs which should be appended for a request.
func (r *Raft) setNewLogs(req *AppendEntriesRequest, nextIndex, lastIndex uint64) error {
// Append up to MaxAppendEntries or up to the lastIndex
req.Entries = make([]*Log, 0, r.conf.MaxAppendEntries)
maxIndex := min(nextIndex+uint64(r.conf.MaxAppendEntries)-1, lastIndex)
for i := nextIndex; i <= maxIndex; i++ {
oldLog := new(Log)
if err := r.logs.GetLog(i, oldLog); err != nil {
r.logger.Printf("[ERR] raft: Failed to get log at index %d: %v", i, err)
return err
}
req.Entries = append(req.Entries, oldLog)
}
return nil
}
// appendStats is used to emit stats about an AppendEntries invocation.
func appendStats(peer string, start time.Time, logs float32) {
metrics.MeasureSince([]string{"raft", "replication", "appendEntries", "rpc", peer}, start)
metrics.IncrCounter([]string{"raft", "replication", "appendEntries", "logs", peer}, logs)
}
// handleStaleTerm is used when a follower indicates that we have a stale term.
func (r *Raft) handleStaleTerm(s *followerReplication) {
r.logger.Printf("[ERR] raft: peer %v has newer term, stopping replication", s.peer)
s.notifyAll(false) // No longer leader
asyncNotifyCh(s.stepDown)
}
// updateLastAppended is used to update follower replication state after a successful
// AppendEntries RPC.
func updateLastAppended(s *followerReplication, req *AppendEntriesRequest) {
// Mark any inflight logs as committed
if logs := req.Entries; len(logs) > 0 {
first := logs[0]
last := logs[len(logs)-1]
s.inflight.CommitRange(first.Index, last.Index)
// Update the indexes
s.matchIndex = last.Index
s.nextIndex = last.Index + 1
}
// Notify still leader
s.notifyAll(true)
}
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