etcd/raft/log.go

/*
   Copyright 2014 CoreOS, Inc.

   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.
	// Invariant: committed < unstable
	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
}

// newLog returns log using the given storage. It recovers the log to the state
// that it just commits and applies the lastest snapshot.
func newLog(storage Storage) *raftLog {
	if storage == nil {
		log.Panic("storage must not be nil")
	}
	log := &raftLog{
		storage: storage,
	}
	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
	// 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.unstable.offset, l.committed, l.applied, 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) {
	lastnewi = index + uint64(len(ents))
	if l.matchTerm(index, logTerm) {
		ci := l.findConflict(ents)
		switch {
		case ci == 0:
		case ci <= l.committed:
			log.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 {
		log.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() {
				log.Printf("raftlog: found conflict at index %d [existing term: %d, conflicting term: %d]",
					ne.Index, 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 {
		return l.slice(off, l.committed+1)
	}
	return nil
}

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 {
			log.Panicf("tocommit(%d) is out of range [lastIndex(%d)]", tocommit, l.lastIndex())
		}
		l.committed = tocommit
	}
}

func (l *raftLog) appliedTo(i uint64) {
	if i == 0 {
		return
	}
	if l.committed < i || i < l.applied {
		log.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 { return l.term(l.lastIndex()) }

func (l *raftLog) term(i uint64) uint64 {
	if i > l.lastIndex() {
		return 0
	}

	if t, ok := l.unstable.maybeTerm(i); ok {
		return t
	}

	t, err := l.storage.Term(i)
	if err == nil {
		return t
	}
	if err == ErrCompacted {
		return 0
	}
	panic(err) // TODO(bdarnell)
}

func (l *raftLog) entries(i uint64) []pb.Entry {
	if i > l.lastIndex() {
		return nil
	}
	return l.slice(i, l.lastIndex()+1)
}

// allEntries returns all entries in the log.
func (l *raftLog) allEntries() []pb.Entry { return l.entries(l.firstIndex()) }

// 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 { return l.term(i) == term }

func (l *raftLog) maybeCommit(maxIndex, term uint64) bool {
	if maxIndex > l.committed && l.term(maxIndex) == term {
		l.commitTo(maxIndex)
		return true
	}
	return false
}

func (l *raftLog) restore(s pb.Snapshot) {
	log.Printf("raftlog: 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 uint64, hi uint64) []pb.Entry {
	l.mustCheckOutOfBounds(lo, hi)
	if lo == hi {
		return nil
	}
	var ents []pb.Entry
	if lo < l.unstable.offset {
		storedEnts, err := l.storage.Entries(lo, min(hi, l.unstable.offset))
		if err == ErrCompacted {
			// This should never fail because it has been checked before.
			log.Panicf("entries[%d:%d) from storage is out of bound", lo, min(hi, l.unstable.offset))
		} else if err == ErrUnavailable {
			log.Panicf("entries[%d:%d) is unavailable from storage", lo, min(hi, l.unstable.offset))
		} else if err != nil {
			panic(err) // TODO(bdarnell)
		}
		ents = append(ents, storedEnts...)
	}
	if hi > l.unstable.offset {
		unstable := l.unstable.slice(max(lo, l.unstable.offset), hi)
		ents = append(ents, unstable...)
	}
	return ents
}

// l.firstIndex <= lo <= hi <= l.firstIndex + len(l.entries)
func (l *raftLog) mustCheckOutOfBounds(lo, hi uint64) {
	if lo > hi {
		log.Panicf("raft: invalid slice %d > %d", lo, hi)
	}
	length := l.lastIndex() - l.firstIndex() + 1
	if lo < l.firstIndex() || hi > l.firstIndex()+length {
		log.Panicf("raft: slice[%d,%d) out of bound [%d,%d]", lo, hi, l.firstIndex(), l.lastIndex())
	}
}