-
Notifications
You must be signed in to change notification settings - Fork 0
/
wal.go
411 lines (361 loc) · 9.66 KB
/
wal.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
package wal
import (
"encoding"
"errors"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strconv"
"strings"
)
var (
// public errors
ErrNoData = fmt.Errorf("no data provided")
ErrEntryNotFound = fmt.Errorf("entry not found")
ErrSeqNumOutOfRange = fmt.Errorf("sequence number is out of range")
// internal errors
errSegmentNotFound = fmt.Errorf("segment not found")
)
type Wal interface {
// Name returns the name of the write ahead log
Name() string
// Read reads the data of the entry with the given sequence number and returns it
Read(_seqNum uint64) ([]byte, error)
// ReadAt reads the data of the entry with the given sequence number to _entry
// Deprecated
ReadAt(_entry Entry, _seqNum uint64) error
// ReadTo reads the data of the entry with the given sequence number to _entry
ReadTo(_entry encoding.BinaryUnmarshaler, _seqNum uint64) error
// ReadFrom reads the payload of _n entries starting from _seqNum
ReadFrom(_seqNum uint64, _n int64) (<-chan Envelope, error)
// Write writes the given data on disk and returns the new sequence number
Write(_data []byte) (uint64, error)
// WriteFrom extracts data from the given object and writes it on disk. it returns the new sequence number
WriteFrom(r encoding.BinaryMarshaler) (uint64, error)
// Truncate dumps all records whose sequence number is greater or equal to offsetByPos
Truncate(_seqNum uint64) error
// Sync flushes changes to persistent storage and returns the latest safe sequence number
Sync() (uint64, error)
// First returns the first sequence number in the write ahead log
First() uint64
// SeqNum returns the latest written sequence number in the write ahead log
SeqNum() uint64
// Safe returns the latest safe sequence number
Safe() uint64
// Close closes the write ahead log and all segment files
Close() error
}
type wal struct {
// name is the name of the write ahead log. all segment files have this as name prefix
name string
// split defines in how many chunks a single filesystem block should be divided
split int64
// size is the max amount of blocks which should be written to a single segment file
size int64
// first is the first sequence number in the write ahead log
first uint64
// seqNum is the latest written sequence number in the write ahead log
seqNum uint64
// segments is a list of segments which belongs to the write ahead log
segments []segpos
}
// Open opens or creates a write ahead log.
// _segBlockN is the amount of records which can be written to a single filesystem page
// _segSize is the amount of records which can be written to the segment file
func Open(_name string, _segBlockN int64, _segSize int64) (Wal, error) {
w := wal{
name: _name,
split: _segBlockN,
size: _segSize,
first: 1,
seqNum: 0,
segments: []segpos{},
}
if err := w.scan(); err != nil {
return nil, err
}
return &w, nil
}
func (w *wal) scan() error {
dir := filepath.Dir(w.name)
fileInfos, err := ioutil.ReadDir(dir)
if err != nil {
return fmt.Errorf("can't read directory: %w", err)
}
first := true
for _, info := range fileInfos {
segName := dir + "/" + info.Name()
if !strings.HasPrefix(segName, w.name) {
continue
}
if !strings.Contains(segName, "_") {
return fmt.Errorf("invalid segment name: %s", segName)
}
split := strings.Split(segName, "_")
// parse the last part of the segment name as sequence number
seqNum, err := strconv.ParseUint(split[len(split)-1], 10, 64) // nolint
if err != nil {
return fmt.Errorf("can't parse seq num from filename: %w", err)
}
seg, err := openSegment(segName, w.split, w.size)
if err != nil {
return err
}
w.segments = append(w.segments, segpos{
segment: seg,
seqNum: seqNum,
})
if first {
w.first = seqNum
first = false
}
}
if len(w.segments) > 0 {
segpos := w.segments[len(w.segments)-1]
w.seqNum = segpos.seqNum + uint64(len(segpos.segment.offsets)-1)
}
return nil
}
func (w *wal) segAdd() error {
firstSegNum := w.seqNum + 1
segmentName := fmt.Sprintf("%s_%d", w.name, firstSegNum)
ns, err := openSegment(segmentName, w.split, w.size)
if err != nil {
return err
}
w.segments = append(w.segments, segpos{
segment: ns,
seqNum: firstSegNum,
})
return nil
}
func (w *wal) segBy(seqNum uint64) (segpos, error) {
if seqNum == 0 {
return segpos{}, errSegmentNotFound
}
for i := len(w.segments) - 1; i >= 0; i-- {
sp := w.segments[i]
if sp.seqNum <= seqNum {
return sp, nil
}
}
return segpos{}, errSegmentNotFound
}
func (w *wal) seg() (*segment, error) {
if len(w.segments) == 0 {
err := w.segAdd()
if err != nil {
return nil, err
}
}
return w.segments[len(w.segments)-1].segment, nil
}
// Name returns the name of the write ahead log
func (w *wal) Name() string {
return w.name
}
// Read reads the data of the entry with the given sequence number and returns it
func (w *wal) Read(_seqNum uint64) ([]byte, error) {
segpos, err := w.segBy(_seqNum)
if err != nil {
if errors.Is(err, errSegmentNotFound) {
return nil, ErrEntryNotFound
}
return nil, err
}
offset, err := segpos.offsetBySeqNum(_seqNum)
if err != nil {
return nil, err
}
_r := record{}
if err := segpos.segment.readAt(&_r, offset); err != nil {
return nil, err
}
return _r.payload, nil
}
// ReadAt reads the data of the entry with the given sequence number to _entry
// Deprecated
func (w *wal) ReadAt(_entry Entry, _seqNum uint64) error {
payload, err := w.Read(_seqNum)
if err != nil {
return err
}
if err := _entry.Unmarshal(payload); err != nil {
return fmt.Errorf("can't unmarshal data: %w", err)
}
return nil
}
// ReadTo reads the data of the entry with the given sequence number to _entry
func (w *wal) ReadTo(_entry encoding.BinaryUnmarshaler, _seqNum uint64) error {
payload, err := w.Read(_seqNum)
if err != nil {
return err
}
if err := _entry.UnmarshalBinary(payload); err != nil {
return fmt.Errorf("can't unmarshal data: %w", err)
}
return nil
}
// ReadFrom reads the payload of _n entries starting from _seqNum
func (w *wal) ReadFrom(_seqNum uint64, _n int64) (<-chan Envelope, error) {
out := make(chan Envelope)
if _seqNum < w.first || _seqNum > w.seqNum {
return nil, ErrSeqNumOutOfRange
}
go func() {
defer close(out)
currSeqNum := _seqNum
// sendN counts the elements which are already send via the out channel
var sendN int64
for {
// return if the next seqNum is larger than the last one written
if currSeqNum > w.seqNum {
return
}
// return if _n elements are send via the channel
if sendN >= _n {
return
}
segpos, err := w.segBy(currSeqNum)
if err != nil {
if errors.Is(err, errSegmentNotFound) {
err = ErrEntryNotFound
}
out <- Envelope{Err: err}
return
}
offset, err := segpos.offsetBySeqNum(currSeqNum)
if err != nil {
out <- Envelope{Err: err}
return
}
env, err := segpos.segment.readFrom(offset, _n)
if err != nil {
out <- Envelope{Err: err}
return
}
for envelope := range env {
c := int64(currSeqNum - _seqNum)
if c >= _n || currSeqNum > w.seqNum {
return
}
if envelope.err != nil {
out <- Envelope{Err: envelope.err}
return
}
out <- Envelope{
SeqNum: currSeqNum,
Payload: envelope.record.payload,
}
sendN++
currSeqNum++
}
}
}()
return out, nil
}
// Write writes the given record on disk and returns the new sequence number
func (w *wal) Write(_data []byte) (uint64, error) {
// check is data is available
if len(_data) == 0 {
return 0, ErrNoData
}
_r := record{payload: _data}
for {
seg, err := w.seg()
if err != nil {
return 0, fmt.Errorf("no segment available: %w", err)
}
// try to write record to segment file
_, err = seg.write(_r)
if err == nil {
break
}
if !errors.Is(err, errMaxSize) {
return 0, fmt.Errorf("couldn't write entry: %w", err)
}
// sync open changes to disk before opening a new segment
if err := seg.sync(); err != nil {
return 0, err
}
err = w.segAdd()
if err != nil {
return 0, fmt.Errorf("no segment available: %w", err)
}
}
w.seqNum++
return w.seqNum, nil
}
// WriteFrom extracts data from the given object and writes it on disk. it returns the new sequence number
func (w *wal) WriteFrom(r encoding.BinaryMarshaler) (uint64, error) {
data, err := r.MarshalBinary()
if err != nil {
return 0, fmt.Errorf("can't marshal data: %w", err)
}
return w.Write(data)
}
func (w *wal) Truncate(_seqNum uint64) error {
defer func() {
w.seqNum = _seqNum - 1
}()
for i := len(w.segments) - 1; i >= 0; i-- {
segpos := w.segments[i]
if segpos.seqNum < _seqNum {
offset, err := segpos.offsetBySeqNum(_seqNum)
if err != nil {
return err
}
return segpos.segment.truncate(offset)
}
// remove segment reference
w.segments = w.segments[:len(w.segments)-1]
_ = segpos.segment.close()
// delete the segment since all elements will be truncated
err := os.Remove(segpos.segment.file.Name())
if err != nil {
return fmt.Errorf("can't remove segment file: %w", err)
}
}
return nil
}
func (w *wal) Sync() (uint64, error) {
seg, err := w.seg()
if err != nil {
return 0, err
}
if err := seg.sync(); err != nil {
return 0, err
}
return w.seqNum, nil
}
func (w *wal) First() uint64 {
return w.first
}
func (w *wal) SeqNum() uint64 {
return w.seqNum
}
func (w *wal) Safe() uint64 {
if len(w.segments) == 0 {
return 0
}
segpos := w.segments[len(w.segments)-1]
seg := segpos.segment
for i, offset := range seg.offsets {
if offset != seg.safe {
continue
}
return segpos.seqNum + uint64(i)
}
return segpos.seqNum - 1
}
func (w *wal) Close() error {
var gerr error
for _, seg := range w.segments {
err := seg.segment.close()
if err != nil {
gerr = err
}
}
return gerr
}