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@xiang90 @gyuho @yichengq @sinsharat @heyitsanthony @tbg @siddontang @shrajfr12 @shawnps @kkaneda @jonboulle
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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 (
"errors"
"sync"
pb "go.etcd.io/etcd/raft/raftpb"
)
// ErrCompacted is returned by Storage.Entries/Compact when a requested
// index is unavailable because it predates the last snapshot.
var ErrCompacted = errors.New("requested index is unavailable due to compaction")
// ErrSnapOutOfDate is returned by Storage.CreateSnapshot when a requested
// index is older than the existing snapshot.
var ErrSnapOutOfDate = errors.New("requested index is older than the existing snapshot")
// ErrUnavailable is returned by Storage interface when the requested log entries
// are unavailable.
var ErrUnavailable = errors.New("requested entry at index is unavailable")
// ErrSnapshotTemporarilyUnavailable is returned by the Storage interface when the required
// snapshot is temporarily unavailable.
var ErrSnapshotTemporarilyUnavailable = errors.New("snapshot is temporarily unavailable")
// Storage is an interface that may be implemented by the application
// to retrieve log entries from storage.
//
// If any Storage method returns an error, the raft instance will
// become inoperable and refuse to participate in elections; the
// application is responsible for cleanup and recovery in this case.
type Storage interface {
// TODO(tbg): split this into two interfaces, LogStorage and StateStorage.
// InitialState returns the saved HardState and ConfState information.
InitialState() (pb.HardState, pb.ConfState, error)
// Entries returns a slice of log entries in the range [lo,hi).
// MaxSize limits the total size of the log entries returned, but
// Entries returns at least one entry if any.
Entries(lo, hi, maxSize uint64) ([]pb.Entry, error)
// Term returns the term of entry i, which must be in the range
// [FirstIndex()-1, LastIndex()]. The term of the entry before
// FirstIndex is retained for matching purposes even though the
// rest of that entry may not be available.
Term(i uint64) (uint64, error)
// LastIndex returns the index of the last entry in the log.
LastIndex() (uint64, error)
// FirstIndex returns the index of the first log entry that is
// possibly available via Entries (older entries have been incorporated
// into the latest Snapshot; if storage only contains the dummy entry the
// first log entry is not available).
FirstIndex() (uint64, error)
// Snapshot returns the most recent snapshot.
// If snapshot is temporarily unavailable, it should return ErrSnapshotTemporarilyUnavailable,
// so raft state machine could know that Storage needs some time to prepare
// snapshot and call Snapshot later.
Snapshot() (pb.Snapshot, error)
}
// MemoryStorage implements the Storage interface backed by an
// in-memory array.
type MemoryStorage struct {
// Protects access to all fields. Most methods of MemoryStorage are
// run on the raft goroutine, but Append() is run on an application
// goroutine.
sync.Mutex
hardState pb.HardState
snapshot pb.Snapshot
// ents[i] has raft log position i+snapshot.Metadata.Index
ents []pb.Entry
}
// NewMemoryStorage creates an empty MemoryStorage.
func NewMemoryStorage() *MemoryStorage {
return &MemoryStorage{
// When starting from scratch populate the list with a dummy entry at term zero.
ents: make([]pb.Entry, 1),
}
}
// InitialState implements the Storage interface.
func (ms *MemoryStorage) InitialState() (pb.HardState, pb.ConfState, error) {
return ms.hardState, ms.snapshot.Metadata.ConfState, nil
}
// SetHardState saves the current HardState.
func (ms *MemoryStorage) SetHardState(st pb.HardState) error {
ms.Lock()
defer ms.Unlock()
ms.hardState = st
return nil
}
// Entries implements the Storage interface.
func (ms *MemoryStorage) Entries(lo, hi, maxSize uint64) ([]pb.Entry, error) {
ms.Lock()
defer ms.Unlock()
offset := ms.ents[0].Index
if lo <= offset {
return nil, ErrCompacted
}
if hi > ms.lastIndex()+1 {
raftLogger.Panicf("entries' hi(%d) is out of bound lastindex(%d)", hi, ms.lastIndex())
}
// only contains dummy entries.
if len(ms.ents) == 1 {
return nil, ErrUnavailable
}
ents := ms.ents[lo-offset : hi-offset]
return limitSize(ents, maxSize), nil
}
// Term implements the Storage interface.
func (ms *MemoryStorage) Term(i uint64) (uint64, error) {
ms.Lock()
defer ms.Unlock()
offset := ms.ents[0].Index
if i < offset {
return 0, ErrCompacted
}
if int(i-offset) >= len(ms.ents) {
return 0, ErrUnavailable
}
return ms.ents[i-offset].Term, nil
}
// LastIndex implements the Storage interface.
func (ms *MemoryStorage) LastIndex() (uint64, error) {
ms.Lock()
defer ms.Unlock()
return ms.lastIndex(), nil
}
func (ms *MemoryStorage) lastIndex() uint64 {
return ms.ents[0].Index + uint64(len(ms.ents)) - 1
}
// FirstIndex implements the Storage interface.
func (ms *MemoryStorage) FirstIndex() (uint64, error) {
ms.Lock()
defer ms.Unlock()
return ms.firstIndex(), nil
}
func (ms *MemoryStorage) firstIndex() uint64 {
return ms.ents[0].Index + 1
}
// Snapshot implements the Storage interface.
func (ms *MemoryStorage) Snapshot() (pb.Snapshot, error) {
ms.Lock()
defer ms.Unlock()
return ms.snapshot, nil
}
// ApplySnapshot overwrites the contents of this Storage object with
// those of the given snapshot.
func (ms *MemoryStorage) ApplySnapshot(snap pb.Snapshot) error {
ms.Lock()
defer ms.Unlock()
//handle check for old snapshot being applied
msIndex := ms.snapshot.Metadata.Index
snapIndex := snap.Metadata.Index
if msIndex >= snapIndex {
return ErrSnapOutOfDate
}
ms.snapshot = snap
ms.ents = []pb.Entry{{Term: snap.Metadata.Term, Index: snap.Metadata.Index}}
return nil
}
// CreateSnapshot makes a snapshot which can be retrieved with Snapshot() and
// can be used to reconstruct the state at that point.
// If any configuration changes have been made since the last compaction,
// the result of the last ApplyConfChange must be passed in.
func (ms *MemoryStorage) CreateSnapshot(i uint64, cs *pb.ConfState, data []byte) (pb.Snapshot, error) {
ms.Lock()
defer ms.Unlock()
if i <= ms.snapshot.Metadata.Index {
return pb.Snapshot{}, ErrSnapOutOfDate
}
offset := ms.ents[0].Index
if i > ms.lastIndex() {
raftLogger.Panicf("snapshot %d is out of bound lastindex(%d)", i, ms.lastIndex())
}
ms.snapshot.Metadata.Index = i
ms.snapshot.Metadata.Term = ms.ents[i-offset].Term
if cs != nil {
ms.snapshot.Metadata.ConfState = *cs
}
ms.snapshot.Data = data
return ms.snapshot, nil
}
// Compact discards all log entries prior to compactIndex.
// It is the application's responsibility to not attempt to compact an index
// greater than raftLog.applied.
func (ms *MemoryStorage) Compact(compactIndex uint64) error {
ms.Lock()
defer ms.Unlock()
offset := ms.ents[0].Index
if compactIndex <= offset {
return ErrCompacted
}
if compactIndex > ms.lastIndex() {
raftLogger.Panicf("compact %d is out of bound lastindex(%d)", compactIndex, ms.lastIndex())
}
i := compactIndex - offset
ents := make([]pb.Entry, 1, 1+uint64(len(ms.ents))-i)
ents[0].Index = ms.ents[i].Index
ents[0].Term = ms.ents[i].Term
ents = append(ents, ms.ents[i+1:]...)
ms.ents = ents
return nil
}
// Append the new entries to storage.
// TODO (xiangli): ensure the entries are continuous and
// entries[0].Index > ms.entries[0].Index
func (ms *MemoryStorage) Append(entries []pb.Entry) error {
if len(entries) == 0 {
return nil
}
ms.Lock()
defer ms.Unlock()
first := ms.firstIndex()
last := entries[0].Index + uint64(len(entries)) - 1
// shortcut if there is no new entry.
if last < first {
return nil
}
// truncate compacted entries
if first > entries[0].Index {
entries = entries[first-entries[0].Index:]
}
offset := entries[0].Index - ms.ents[0].Index
switch {
case uint64(len(ms.ents)) > offset:
ms.ents = append([]pb.Entry{}, ms.ents[:offset]...)
ms.ents = append(ms.ents, entries...)
case uint64(len(ms.ents)) == offset:
ms.ents = append(ms.ents, entries...)
default:
raftLogger.Panicf("missing log entry [last: %d, append at: %d]",
ms.lastIndex(), entries[0].Index)
}
return nil
}
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