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log.go
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log.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 (
"fmt"
"log"
pb "github.com/coreos/etcd/raft/raftpb"
)
type raftLog struct {
// storage contains all stable entries since the last snapshot.
storage Storage
// unstable contains all unstable entries and snapshot.
// they will be saved into storage.
unstable unstable
// committed is the highest log position that is known to be in
// stable storage on a quorum of nodes.
committed uint64
// applied is the highest log position that the application has
// been instructed to apply to its state machine.
// Invariant: applied <= committed
applied uint64
logger Logger
}
// newLog returns log using the given storage. It recovers the log to the state
// that it just commits and applies the latest snapshot.
func newLog(storage Storage, logger Logger) *raftLog {
if storage == nil {
log.Panic("storage must not be nil")
}
log := &raftLog{
storage: storage,
logger: logger,
}
firstIndex, err := storage.FirstIndex()
if err != nil {
panic(err) // TODO(bdarnell)
}
lastIndex, err := storage.LastIndex()
if err != nil {
panic(err) // TODO(bdarnell)
}
log.unstable.offset = lastIndex + 1
log.unstable.logger = logger
// Initialize our committed and applied pointers to the time of the last compaction.
log.committed = firstIndex - 1
log.applied = firstIndex - 1
return log
}
func (l *raftLog) String() string {
return fmt.Sprintf("committed=%d, applied=%d, unstable.offset=%d, len(unstable.Entries)=%d", l.committed, l.applied, l.unstable.offset, len(l.unstable.entries))
}
// maybeAppend returns (0, false) if the entries cannot be appended. Otherwise,
// it returns (last index of new entries, true).
func (l *raftLog) maybeAppend(index, logTerm, committed uint64, ents ...pb.Entry) (lastnewi uint64, ok bool) {
if l.matchTerm(index, logTerm) {
lastnewi = index + uint64(len(ents))
ci := l.findConflict(ents)
switch {
case ci == 0:
case ci <= l.committed:
l.logger.Panicf("entry %d conflict with committed entry [committed(%d)]", ci, l.committed)
default:
offset := index + 1
l.append(ents[ci-offset:]...)
}
l.commitTo(min(committed, lastnewi))
return lastnewi, true
}
return 0, false
}
func (l *raftLog) append(ents ...pb.Entry) uint64 {
if len(ents) == 0 {
return l.lastIndex()
}
if after := ents[0].Index - 1; after < l.committed {
l.logger.Panicf("after(%d) is out of range [committed(%d)]", after, l.committed)
}
l.unstable.truncateAndAppend(ents)
return l.lastIndex()
}
// findConflict finds the index of the conflict.
// It returns the first pair of conflicting entries between the existing
// entries and the given entries, if there are any.
// If there is no conflicting entries, and the existing entries contains
// all the given entries, zero will be returned.
// If there is no conflicting entries, but the given entries contains new
// entries, the index of the first new entry will be returned.
// An entry is considered to be conflicting if it has the same index but
// a different term.
// The first entry MUST have an index equal to the argument 'from'.
// The index of the given entries MUST be continuously increasing.
func (l *raftLog) findConflict(ents []pb.Entry) uint64 {
for _, ne := range ents {
if !l.matchTerm(ne.Index, ne.Term) {
if ne.Index <= l.lastIndex() {
l.logger.Infof("found conflict at index %d [existing term: %d, conflicting term: %d]",
ne.Index, l.zeroTermOnErrCompacted(l.term(ne.Index)), ne.Term)
}
return ne.Index
}
}
return 0
}
func (l *raftLog) unstableEntries() []pb.Entry {
if len(l.unstable.entries) == 0 {
return nil
}
return l.unstable.entries
}
// nextEnts returns all the available entries for execution.
// If applied is smaller than the index of snapshot, it returns all committed
// entries after the index of snapshot.
func (l *raftLog) nextEnts() (ents []pb.Entry) {
off := max(l.applied+1, l.firstIndex())
if l.committed+1 > off {
ents, err := l.slice(off, l.committed+1, noLimit)
if err != nil {
l.logger.Panicf("unexpected error when getting unapplied entries (%v)", err)
}
return ents
}
return nil
}
// hasNextEnts returns if there is any available entries for execution. This
// is a fast check without heavy raftLog.slice() in raftLog.nextEnts().
func (l *raftLog) hasNextEnts() bool {
off := max(l.applied+1, l.firstIndex())
return l.committed+1 > off
}
func (l *raftLog) snapshot() (pb.Snapshot, error) {
if l.unstable.snapshot != nil {
return *l.unstable.snapshot, nil
}
return l.storage.Snapshot()
}
func (l *raftLog) firstIndex() uint64 {
if i, ok := l.unstable.maybeFirstIndex(); ok {
return i
}
index, err := l.storage.FirstIndex()
if err != nil {
panic(err) // TODO(bdarnell)
}
return index
}
func (l *raftLog) lastIndex() uint64 {
if i, ok := l.unstable.maybeLastIndex(); ok {
return i
}
i, err := l.storage.LastIndex()
if err != nil {
panic(err) // TODO(bdarnell)
}
return i
}
func (l *raftLog) commitTo(tocommit uint64) {
// never decrease commit
if l.committed < tocommit {
if l.lastIndex() < tocommit {
l.logger.Panicf("tocommit(%d) is out of range [lastIndex(%d)]. Was the raft log corrupted, truncated, or lost?", tocommit, l.lastIndex())
}
l.committed = tocommit
}
}
func (l *raftLog) appliedTo(i uint64) {
if i == 0 {
return
}
if l.committed < i || i < l.applied {
l.logger.Panicf("applied(%d) is out of range [prevApplied(%d), committed(%d)]", i, l.applied, l.committed)
}
l.applied = i
}
func (l *raftLog) stableTo(i, t uint64) { l.unstable.stableTo(i, t) }
func (l *raftLog) stableSnapTo(i uint64) { l.unstable.stableSnapTo(i) }
func (l *raftLog) lastTerm() uint64 {
t, err := l.term(l.lastIndex())
if err != nil {
l.logger.Panicf("unexpected error when getting the last term (%v)", err)
}
return t
}
func (l *raftLog) term(i uint64) (uint64, error) {
// the valid term range is [index of dummy entry, last index]
dummyIndex := l.firstIndex() - 1
if i < dummyIndex || i > l.lastIndex() {
// TODO: return an error instead?
return 0, nil
}
if t, ok := l.unstable.maybeTerm(i); ok {
return t, nil
}
t, err := l.storage.Term(i)
if err == nil {
return t, nil
}
if err == ErrCompacted || err == ErrUnavailable {
return 0, err
}
panic(err) // TODO(bdarnell)
}
func (l *raftLog) entries(i, maxsize uint64) ([]pb.Entry, error) {
if i > l.lastIndex() {
return nil, nil
}
return l.slice(i, l.lastIndex()+1, maxsize)
}
// allEntries returns all entries in the log.
func (l *raftLog) allEntries() []pb.Entry {
ents, err := l.entries(l.firstIndex(), noLimit)
if err == nil {
return ents
}
if err == ErrCompacted { // try again if there was a racing compaction
return l.allEntries()
}
// TODO (xiangli): handle error?
panic(err)
}
// isUpToDate determines if the given (lastIndex,term) log is more up-to-date
// by comparing the index and term of the last entries in the existing logs.
// If the logs have last entries with different terms, then the log with the
// later term is more up-to-date. If the logs end with the same term, then
// whichever log has the larger lastIndex is more up-to-date. If the logs are
// the same, the given log is up-to-date.
func (l *raftLog) isUpToDate(lasti, term uint64) bool {
return term > l.lastTerm() || (term == l.lastTerm() && lasti >= l.lastIndex())
}
func (l *raftLog) matchTerm(i, term uint64) bool {
t, err := l.term(i)
if err != nil {
return false
}
return t == term
}
func (l *raftLog) maybeCommit(maxIndex, term uint64) bool {
if maxIndex > l.committed && l.zeroTermOnErrCompacted(l.term(maxIndex)) == term {
l.commitTo(maxIndex)
return true
}
return false
}
func (l *raftLog) restore(s pb.Snapshot) {
l.logger.Infof("log [%s] starts to restore snapshot [index: %d, term: %d]", l, s.Metadata.Index, s.Metadata.Term)
l.committed = s.Metadata.Index
l.unstable.restore(s)
}
// slice returns a slice of log entries from lo through hi-1, inclusive.
func (l *raftLog) slice(lo, hi, maxSize uint64) ([]pb.Entry, error) {
err := l.mustCheckOutOfBounds(lo, hi)
if err != nil {
return nil, err
}
if lo == hi {
return nil, nil
}
var ents []pb.Entry
if lo < l.unstable.offset {
storedEnts, err := l.storage.Entries(lo, min(hi, l.unstable.offset), maxSize)
if err == ErrCompacted {
return nil, err
} else if err == ErrUnavailable {
l.logger.Panicf("entries[%d:%d) is unavailable from storage", lo, min(hi, l.unstable.offset))
} else if err != nil {
panic(err) // TODO(bdarnell)
}
// check if ents has reached the size limitation
if uint64(len(storedEnts)) < min(hi, l.unstable.offset)-lo {
return storedEnts, nil
}
ents = storedEnts
}
if hi > l.unstable.offset {
unstable := l.unstable.slice(max(lo, l.unstable.offset), hi)
if len(ents) > 0 {
ents = append([]pb.Entry{}, ents...)
ents = append(ents, unstable...)
} else {
ents = unstable
}
}
return limitSize(ents, maxSize), nil
}
// l.firstIndex <= lo <= hi <= l.firstIndex + len(l.entries)
func (l *raftLog) mustCheckOutOfBounds(lo, hi uint64) error {
if lo > hi {
l.logger.Panicf("invalid slice %d > %d", lo, hi)
}
fi := l.firstIndex()
if lo < fi {
return ErrCompacted
}
length := l.lastIndex() + 1 - fi
if lo < fi || hi > fi+length {
l.logger.Panicf("slice[%d,%d) out of bound [%d,%d]", lo, hi, fi, l.lastIndex())
}
return nil
}
func (l *raftLog) zeroTermOnErrCompacted(t uint64, err error) uint64 {
if err == nil {
return t
}
if err == ErrCompacted {
return 0
}
l.logger.Panicf("unexpected error (%v)", err)
return 0
}