1// Copyright 2015 The etcd Authors 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14 15package raft 16 17import ( 18 "errors" 19 "sync" 20 21 pb "github.com/coreos/etcd/raft/raftpb" 22) 23 24// ErrCompacted is returned by Storage.Entries/Compact when a requested 25// index is unavailable because it predates the last snapshot. 26var ErrCompacted = errors.New("requested index is unavailable due to compaction") 27 28// ErrSnapOutOfDate is returned by Storage.CreateSnapshot when a requested 29// index is older than the existing snapshot. 30var ErrSnapOutOfDate = errors.New("requested index is older than the existing snapshot") 31 32// ErrUnavailable is returned by Storage interface when the requested log entries 33// are unavailable. 34var ErrUnavailable = errors.New("requested entry at index is unavailable") 35 36// ErrSnapshotTemporarilyUnavailable is returned by the Storage interface when the required 37// snapshot is temporarily unavailable. 38var ErrSnapshotTemporarilyUnavailable = errors.New("snapshot is temporarily unavailable") 39 40// Storage is an interface that may be implemented by the application 41// to retrieve log entries from storage. 42// 43// If any Storage method returns an error, the raft instance will 44// become inoperable and refuse to participate in elections; the 45// application is responsible for cleanup and recovery in this case. 46type Storage interface { 47 // InitialState returns the saved HardState and ConfState information. 48 InitialState() (pb.HardState, pb.ConfState, error) 49 // Entries returns a slice of log entries in the range [lo,hi). 50 // MaxSize limits the total size of the log entries returned, but 51 // Entries returns at least one entry if any. 52 Entries(lo, hi, maxSize uint64) ([]pb.Entry, error) 53 // Term returns the term of entry i, which must be in the range 54 // [FirstIndex()-1, LastIndex()]. The term of the entry before 55 // FirstIndex is retained for matching purposes even though the 56 // rest of that entry may not be available. 57 Term(i uint64) (uint64, error) 58 // LastIndex returns the index of the last entry in the log. 59 LastIndex() (uint64, error) 60 // FirstIndex returns the index of the first log entry that is 61 // possibly available via Entries (older entries have been incorporated 62 // into the latest Snapshot; if storage only contains the dummy entry the 63 // first log entry is not available). 64 FirstIndex() (uint64, error) 65 // Snapshot returns the most recent snapshot. 66 // If snapshot is temporarily unavailable, it should return ErrSnapshotTemporarilyUnavailable, 67 // so raft state machine could know that Storage needs some time to prepare 68 // snapshot and call Snapshot later. 69 Snapshot() (pb.Snapshot, error) 70} 71 72// MemoryStorage implements the Storage interface backed by an 73// in-memory array. 74type MemoryStorage struct { 75 // Protects access to all fields. Most methods of MemoryStorage are 76 // run on the raft goroutine, but Append() is run on an application 77 // goroutine. 78 sync.Mutex 79 80 hardState pb.HardState 81 snapshot pb.Snapshot 82 // ents[i] has raft log position i+snapshot.Metadata.Index 83 ents []pb.Entry 84} 85 86// NewMemoryStorage creates an empty MemoryStorage. 87func NewMemoryStorage() *MemoryStorage { 88 return &MemoryStorage{ 89 // When starting from scratch populate the list with a dummy entry at term zero. 90 ents: make([]pb.Entry, 1), 91 } 92} 93 94// InitialState implements the Storage interface. 95func (ms *MemoryStorage) InitialState() (pb.HardState, pb.ConfState, error) { 96 return ms.hardState, ms.snapshot.Metadata.ConfState, nil 97} 98 99// SetHardState saves the current HardState. 100func (ms *MemoryStorage) SetHardState(st pb.HardState) error { 101 ms.hardState = st 102 return nil 103} 104 105// Entries implements the Storage interface. 106func (ms *MemoryStorage) Entries(lo, hi, maxSize uint64) ([]pb.Entry, error) { 107 ms.Lock() 108 defer ms.Unlock() 109 offset := ms.ents[0].Index 110 if lo <= offset { 111 return nil, ErrCompacted 112 } 113 if hi > ms.lastIndex()+1 { 114 raftLogger.Panicf("entries' hi(%d) is out of bound lastindex(%d)", hi, ms.lastIndex()) 115 } 116 // only contains dummy entries. 117 if len(ms.ents) == 1 { 118 return nil, ErrUnavailable 119 } 120 121 ents := ms.ents[lo-offset : hi-offset] 122 return limitSize(ents, maxSize), nil 123} 124 125// Term implements the Storage interface. 126func (ms *MemoryStorage) Term(i uint64) (uint64, error) { 127 ms.Lock() 128 defer ms.Unlock() 129 offset := ms.ents[0].Index 130 if i < offset { 131 return 0, ErrCompacted 132 } 133 if int(i-offset) >= len(ms.ents) { 134 return 0, ErrUnavailable 135 } 136 return ms.ents[i-offset].Term, nil 137} 138 139// LastIndex implements the Storage interface. 140func (ms *MemoryStorage) LastIndex() (uint64, error) { 141 ms.Lock() 142 defer ms.Unlock() 143 return ms.lastIndex(), nil 144} 145 146func (ms *MemoryStorage) lastIndex() uint64 { 147 return ms.ents[0].Index + uint64(len(ms.ents)) - 1 148} 149 150// FirstIndex implements the Storage interface. 151func (ms *MemoryStorage) FirstIndex() (uint64, error) { 152 ms.Lock() 153 defer ms.Unlock() 154 return ms.firstIndex(), nil 155} 156 157func (ms *MemoryStorage) firstIndex() uint64 { 158 return ms.ents[0].Index + 1 159} 160 161// Snapshot implements the Storage interface. 162func (ms *MemoryStorage) Snapshot() (pb.Snapshot, error) { 163 ms.Lock() 164 defer ms.Unlock() 165 return ms.snapshot, nil 166} 167 168// ApplySnapshot overwrites the contents of this Storage object with 169// those of the given snapshot. 170func (ms *MemoryStorage) ApplySnapshot(snap pb.Snapshot) error { 171 ms.Lock() 172 defer ms.Unlock() 173 174 //handle check for old snapshot being applied 175 msIndex := ms.snapshot.Metadata.Index 176 snapIndex := snap.Metadata.Index 177 if msIndex >= snapIndex { 178 return ErrSnapOutOfDate 179 } 180 181 ms.snapshot = snap 182 ms.ents = []pb.Entry{{Term: snap.Metadata.Term, Index: snap.Metadata.Index}} 183 return nil 184} 185 186// CreateSnapshot makes a snapshot which can be retrieved with Snapshot() and 187// can be used to reconstruct the state at that point. 188// If any configuration changes have been made since the last compaction, 189// the result of the last ApplyConfChange must be passed in. 190func (ms *MemoryStorage) CreateSnapshot(i uint64, cs *pb.ConfState, data []byte) (pb.Snapshot, error) { 191 ms.Lock() 192 defer ms.Unlock() 193 if i <= ms.snapshot.Metadata.Index { 194 return pb.Snapshot{}, ErrSnapOutOfDate 195 } 196 197 offset := ms.ents[0].Index 198 if i > ms.lastIndex() { 199 raftLogger.Panicf("snapshot %d is out of bound lastindex(%d)", i, ms.lastIndex()) 200 } 201 202 ms.snapshot.Metadata.Index = i 203 ms.snapshot.Metadata.Term = ms.ents[i-offset].Term 204 if cs != nil { 205 ms.snapshot.Metadata.ConfState = *cs 206 } 207 ms.snapshot.Data = data 208 return ms.snapshot, nil 209} 210 211// Compact discards all log entries prior to compactIndex. 212// It is the application's responsibility to not attempt to compact an index 213// greater than raftLog.applied. 214func (ms *MemoryStorage) Compact(compactIndex uint64) error { 215 ms.Lock() 216 defer ms.Unlock() 217 offset := ms.ents[0].Index 218 if compactIndex <= offset { 219 return ErrCompacted 220 } 221 if compactIndex > ms.lastIndex() { 222 raftLogger.Panicf("compact %d is out of bound lastindex(%d)", compactIndex, ms.lastIndex()) 223 } 224 225 i := compactIndex - offset 226 ents := make([]pb.Entry, 1, 1+uint64(len(ms.ents))-i) 227 ents[0].Index = ms.ents[i].Index 228 ents[0].Term = ms.ents[i].Term 229 ents = append(ents, ms.ents[i+1:]...) 230 ms.ents = ents 231 return nil 232} 233 234// Append the new entries to storage. 235// TODO (xiangli): ensure the entries are continuous and 236// entries[0].Index > ms.entries[0].Index 237func (ms *MemoryStorage) Append(entries []pb.Entry) error { 238 if len(entries) == 0 { 239 return nil 240 } 241 242 ms.Lock() 243 defer ms.Unlock() 244 245 first := ms.firstIndex() 246 last := entries[0].Index + uint64(len(entries)) - 1 247 248 // shortcut if there is no new entry. 249 if last < first { 250 return nil 251 } 252 // truncate compacted entries 253 if first > entries[0].Index { 254 entries = entries[first-entries[0].Index:] 255 } 256 257 offset := entries[0].Index - ms.ents[0].Index 258 switch { 259 case uint64(len(ms.ents)) > offset: 260 ms.ents = append([]pb.Entry{}, ms.ents[:offset]...) 261 ms.ents = append(ms.ents, entries...) 262 case uint64(len(ms.ents)) == offset: 263 ms.ents = append(ms.ents, entries...) 264 default: 265 raftLogger.Panicf("missing log entry [last: %d, append at: %d]", 266 ms.lastIndex(), entries[0].Index) 267 } 268 return nil 269} 270