etcd/raft/log_unstable.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 (
	"log"

	pb "github.com/coreos/etcd/raft/raftpb"
)

// unstable.entris[i] has raft log position i+unstable.offset.
// Note that unstable.offset may be less than the highest log
// position in storage; this means that the next write to storage
// might need to truncate the log before persisting unstable.entries.
type unstable struct {
	// the incoming unstable snapshot, if any.
	snapshot *pb.Snapshot
	// all entries that have not yet been written to storage.
	entries []pb.Entry
	offset  uint64
}

// maybeFirstIndex returns the index of the first possible entry in entries
// if it has a snapshot.
func (u *unstable) maybeFirstIndex() (uint64, bool) {
	if u.snapshot != nil {
		return u.snapshot.Metadata.Index + 1, true
	}
	return 0, false
}

// maybeLastIndex returns the last index if it has at least one
// unstable entry or snapshot.
func (u *unstable) maybeLastIndex() (uint64, bool) {
	if l := len(u.entries); l != 0 {
		return u.offset + uint64(l) - 1, true
	}
	if u.snapshot != nil {
		return u.snapshot.Metadata.Index, true
	}
	return 0, false
}

// myabeTerm returns the term of the entry at index i, if there
// is any.
func (u *unstable) maybeTerm(i uint64) (uint64, bool) {
	if i < u.offset {
		if u.snapshot == nil {
			return 0, false
		}
		if u.snapshot.Metadata.Index == i {
			return u.snapshot.Metadata.Term, true
		}
		return 0, false
	}

	last, ok := u.maybeLastIndex()
	if !ok {
		return 0, false
	}
	if i > last {
		return 0, false
	}
	return u.entries[i-u.offset].Term, true
}

func (u *unstable) stableTo(i, t uint64) {
	gt, ok := u.maybeTerm(i)
	if !ok {
		return
	}
	// if i < offest, term is matched with the snapshot
	// only update the unstalbe entries if term is matched with
	// an unstable entry.
	if gt == t && i >= u.offset {
		u.entries = u.entries[i+1-u.offset:]
		u.offset = i + 1
	}
}

func (u *unstable) stableSnapTo(i uint64) {
	if u.snapshot != nil && u.snapshot.Metadata.Index == i {
		u.snapshot = nil
	}
}

func (u *unstable) restore(s pb.Snapshot) {
	u.offset = s.Metadata.Index + 1
	u.entries = nil
	u.snapshot = &s
}

func (u *unstable) truncateAndAppend(ents []pb.Entry) {
	after := ents[0].Index - 1
	switch {
	case after == u.offset+uint64(len(u.entries))-1:
		// after is the last index in the u.entries
		// directly append
		u.entries = append(u.entries, ents...)
	case after < u.offset:
		log.Printf("raftlog: replace the unstable entries from index %d", after+1)
		// The log is being truncated to before our current offset
		// portion, so set the offset and replace the entries
		u.offset = after + 1
		u.entries = ents
	default:
		// truncate to after and copy to u.entries
		// then append
		log.Printf("raftlog: truncate the unstable entries to index %d", after)
		u.entries = append([]pb.Entry{}, u.slice(u.offset, after+1)...)
		u.entries = append(u.entries, ents...)
	}
}

func (u *unstable) slice(lo uint64, hi uint64) []pb.Entry {
	if lo >= hi {
		return nil
	}
	if u.isOutOfBounds(lo) || u.isOutOfBounds(hi-1) {
		return nil
	}
	return u.entries[lo-u.offset : hi-u.offset]
}

func (u *unstable) isOutOfBounds(i uint64) bool {
	if len(u.entries) == 0 {
		return true
	}
	last := u.offset + uint64(len(u.entries)) - 1
	if i < u.offset || i > last {
		return true
	}
	return false
}