Optimized reads

Total rewrite of the Read operation. There is now a segment LRU cache instead of multiple readers. This has more memory overhead, because up to four segments may be loaded in memory at one time, but is a ton faster and allows for forward and reverse sequential reads. This commit also removes the Durability option in favor of a simpiler NoSync option.

tidwall committed 6 years ago

Commit d1f90551 parent 9c440815 files · +807 −565Browse files

Unified · Split

5 files

README.md +37 −9
go.mod +8 −0
go.sum +8 −0
wal.go +482 −481
wal_test.go +272 −75

README.md+37−9

@@ -1,14 +1,14 @@
1	1	# `wal`
2	2	[![GoDoc](https://godoc.org/github.com/tidwall/wal?status.svg)](https://godoc.org/github.com/tidwall/wal)
3	3
4		−Write ahead log for Go.
	4	+A simple and fast write ahead log for Go.
5	5
6	6	## Features
7	7
8	8	- High durability
9		−- Fast writes
10		−- Low memory footprint
	9	+- Fast operations
11	10	- Monotonic indexes
	11	+- Batch writes
12	12	- Log truncation from front or back.
13	13
14	14	## Getting Started
@@ -27,21 +27,49 @@ This will retrieve the library. · 12 unmodified lines
27	27
28	28	```go
29	29	// open a new log file
30		−l, _ := Open("mylog", nil)
	30	+log, err := Open("mylog", nil)
31	31
32	32	// write some entries
33		−l.Write(1, []byte("first entry"))
34		−l.Write(2, []byte("second entry"))
35		−l.Write(3, []byte("third entry"))
	33	+err = log.Write(1, []byte("first entry"))
	34	+err = log.Write(2, []byte("second entry"))
	35	+err = log.Write(3, []byte("third entry"))
36	36
37	37	// read an entry
38		−data, _ := l.Read(1)
	38	+data, err := log.Read(1)
39	39	println(string(data)) // output: first entry
40	40
41	41	// close the log
42		−l.Close()
	42	+err = log.Close()
43	43	```
44	44
	45	+Batch writes:
	46	+
	47	+```go
	48	+
	49	+// write three entries as a batch
	50	+batch := new(Batch)
	51	+batch.Write(1, []byte("first entry"))
	52	+batch.Write(2, []byte("second entry"))
	53	+batch.Write(3, []byte("third entry"))
	54	+
	55	+err = log.WriteBatch(batch)
	56	+```
	57	+
	58	+Truncating:
	59	+
	60	+```go
	61	+// write some entries
	62	+err = log.Write(1, []byte("first entry"))
	63	+...
	64	+err = log.Write(1000, []byte("thousandth entry"))
	65	+
	66	+// truncate the log from index starting 350 and ending with 950.
	67	+err = l.TruncateFront(350)
	68	+err = l.TruncateBack(950)
	69	+```
	70	+
	71	+
	72	+
45	73	## Contact
46	74
47	75	Josh Baker [@tidwall](http://twitter.com/tidwall)

go.mod+8−0

@@ -0,0 +1,8 @@
	1	+module github.com/tidwall/wal
	2	+
	3	+go 1.13
	4	+
	5	+require (
	6	+ github.com/tidwall/gjson v1.5.0
	7	+ github.com/tidwall/tinylru v1.0.2
	8	+)

go.sum+8−0

@@ -0,0 +1,8 @@
	1	+github.com/tidwall/gjson v1.5.0 h1:QCssIUI7J0RStkzIcI4A7O6P8rDA5wi5IPf70uqKSxg=
	2	+github.com/tidwall/gjson v1.5.0/go.mod h1:P256ACg0Mn+j1RXIDXoss50DeIABTYK1PULOJHhxOls=
	3	+github.com/tidwall/match v1.0.1 h1:PnKP62LPNxHKTwvHHZZzdOAOCtsJTjo6dZLCwpKm5xc=
	4	+github.com/tidwall/match v1.0.1/go.mod h1:LujAq0jyVjBy028G1WhWfIzbpQfMO8bBZ6Tyb0+pL9E=
	5	+github.com/tidwall/pretty v1.0.0 h1:HsD+QiTn7sK6flMKIvNmpqz1qrpP3Ps6jOKIKMooyg4=
	6	+github.com/tidwall/pretty v1.0.0/go.mod h1:XNkn88O1ChpSDQmQeStsy+sBenx6DDtFZJxhVysOjyk=
	7	+github.com/tidwall/tinylru v1.0.2 h1:W4mp7iUz4cnVMqAvWy2zbzC35ASv5sqdyyEjoQKKBFg=
	8	+github.com/tidwall/tinylru v1.0.2/go.mod h1:HDVL7TsWeezQ4g44Um84TOVBMFcq7Xa9giqNc805KJ8=

wal.go+482−481

@@ -1,20 +1,23 @@
1	1	package wal
2	2
3	3	import (
4		− "bufio"
	4	+ "bytes"
5	5	"encoding/base64"
6	6	"encoding/binary"
7	7	"encoding/json"
8	8	"errors"
9	9	"fmt"
10		− "io"
11	10	"io/ioutil"
12	11	"os"
13	12	"path/filepath"
14	13	"strconv"
15	14	"strings"
	15	+ "sync"
16	16	"unicode/utf8"
17	17	"unsafe"
	18	+
	19	+ "github.com/tidwall/gjson"
	20	+ "github.com/tidwall/tinylru"
18	21	)
19	22
20	23	var (
@@ -42,22 +45,6 @@ var ( · 21 unmodified lines
42	45	ErrOutOfRange = errors.New("out of range")
43	46	)
44	47
45		−// Durability policy.
46		−type Durability int8
47		−
48		−const (
49		− // Low durability flushes data to operating system only when the buffer is
50		− // at capacity. A process crash could cause data loss.
51		− Low Durability = -1
52		− // Medium durability flushes data to the operating system after every
53		− // new entry is addded to the log. A server crash could cause data loss.
54		− Medium Durability = 0
55		− // High durability syncs data to disk after every new entry is added to
56		− // the log. All entries are persisted to disk and crashes will not cause
57		− // data loss.
58		− High Durability = 1
59		−)
60		−
61	48	// LogFormat is the format of the log files.
62	49	type LogFormat byte
63	50
@@ -72,49 +59,54 @@ const ( · 8 unmodified lines
72	59
73	60	// Options for Log
74	61	type Options struct {
75		− // Durability policy. Default is High.
76		− Durability Durability
	62	+ // NoSync disables fsync after writes. This is less durable and puts the
	63	+ // log at risk of data loss when there's a server crash.
	64	+ NoSync bool
77	65	// SegmentSize of each segment. This is just a target value, actual size
78		− // may differ. Default is 50 MB.
	66	+ // may differ. Default is 20 MB.
79	67	SegmentSize int
80	68	// LogFormat is the format of the log files. Default is Binary.
81	69	LogFormat LogFormat
	70	+ // SegmentCacheSize is the maximum number of segments that will be held in
	71	+ // memory for caching. Increasing this value may enhance performance for
	72	+ // concurrent read operations. Default is 1
	73	+ SegmentCacheSize int
82	74	}
83	75
84	76	// DefaultOptions for Open().
85	77	var DefaultOptions = &Options{
86		− Durability: High, // Fsync after every write
87		− SegmentSize: 52428800, // 50 MB log segment files.
88		− LogFormat: Binary, // Binary format is small and fast.
	78	+ NoSync: false, // Fsync after every write
	79	+ SegmentSize: 20971520, // 20 MB log segment files.
	80	+ LogFormat: Binary, // Binary format is small and fast.
	81	+ SegmentCacheSize: 1, // Number of cached in-memory segments
89	82	}
90	83
91		−const maxReaders = 8 // maximum number of opened readers.
92		−
93	84	// Log represents a write ahead log
94	85	type Log struct {
95		− path string // absolute path to log directory
96		− opts Options // log options
97		− closed bool // log is closed
98		− segments []segment // all known log segments
99		− firstIndex uint64 // index of the first entry in log
100		− lastIndex uint64 // index of the last entry in log
101		− file *os.File // tail segment file handle
102		− buffer []byte // tail segment file write buffer
103		− fileSize int // tail segment file size, including buffer
104		− readers []*reader // all opened readers
	86	+ mu sync.Mutex
	87	+ path string // absolute path to log directory
	88	+ opts Options // log options
	89	+ closed bool // log is closed
	90	+ corrupt bool // log may be corrupt
	91	+ segments []*segment // all known log segments
	92	+ firstIndex uint64 // index of the first entry in log
	93	+ lastIndex uint64 // index of the last entry in log
	94	+ sfile *os.File // tail segment file handle
	95	+ wbatch Batch // reusable write batch
	96	+ scache tinylru.LRU // segment entries cache
105	97	}
106	98
107	99	// segment represents a single segment file.
108	100	type segment struct {
109	101	path string // path of segment file
110	102	index uint64 // first index of segment
	103	+ ebuf []byte // cached entries buffer
	104	+ epos []bpos // cached entries positions in buffer
111	105	}
112	106
113		−type reader struct {
114		− sindex int // segment index
115		− nindex uint64 // next entry index
116		− file *os.File // opened file
117		− rd *bufio.Reader // reader
	107	+type bpos struct {
	108	+ pos int // byte position
	109	+ end int // one byte past pos
118	110	}
119	111
120	112	// Open a new write ahead log
@@ -122,13 +114,22 @@ func Open(path string, opts Options) (Log, error) { · 1 unmodified line
122	114	if opts == nil {
123	115	opts = DefaultOptions
124	116	}
	117	+ if opts.SegmentCacheSize <= 0 {
	118	+ opts.SegmentCacheSize = DefaultOptions.SegmentCacheSize
	119	+ }
	120	+ if opts.SegmentSize <= 0 {
	121	+ opts.SegmentSize = DefaultOptions.SegmentSize
	122	+ }
125	123	var err error
126	124	path, err = abs(path)
127	125	if err != nil {
128	126	return nil, err
129	127	}
130	128	l := &Log{path: path, opts: *opts}
131		− _ = os.MkdirAll(path, 0777)
	129	+ l.scache.Resize(l.opts.SegmentCacheSize)
	130	+ if err := os.MkdirAll(path, 0777); err != nil {
	131	+ return nil, err
	132	+ }
132	133	if err := l.load(); err != nil {
133	134	return nil, err
134	135	}
@@ -142,6 +143,16 @@ func abs(path string) (string, error) { · 7 unmodified lines
142	143	return filepath.Abs(path)
143	144	}
144	145
	146	+func (l *Log) pushCache(segIdx int) {
	147	+ _, _, _, v, evicted :=
	148	+ l.scache.SetEvicted(segIdx, l.segments[segIdx])
	149	+ if evicted {
	150	+ s := v.(*segment)
	151	+ s.ebuf = nil
	152	+ s.epos = nil
	153	+ }
	154	+}
	155	+
145	156	// load all the segments. This operation also cleansup any START/END segments.
146	157	func (l *Log) load() error {
147	158	fis, err := ioutil.ReadDir(l.path)
@@ -167,7 +178,7 @@ func (l *Log) load() error { · 19 unmodified lines
167	178	} else if isEnd && endIdx == -1 {
168	179	endIdx = len(l.segments)
169	180	}
170		− l.segments = append(l.segments, segment{
	181	+ l.segments = append(l.segments, &segment{
171	182	index: index,
172	183	path: filepath.Join(l.path, name),
173	184	})
@@ -175,13 +186,13 @@ func (l *Log) load() error { · 1 unmodified line
175	186	}
176	187	if len(l.segments) == 0 {
177	188	// Create a new log
178		− l.segments = append(l.segments, segment{
	189	+ l.segments = append(l.segments, &segment{
179	190	index: 1,
180	191	path: filepath.Join(l.path, segmentName(1)),
181	192	})
182	193	l.firstIndex = 1
183	194	l.lastIndex = 0
184		− l.file, err = os.Create(l.segments[0].path)
	195	+ l.sfile, err = os.Create(l.segments[0].path)
185	196	return err
186	197	}
187	198	// Open existing log. Clean up log if START of END segments exists.
@@ -196,7 +207,7 @@ func (l *Log) load() error { · 8 unmodified lines
196	207	return err
197	208	}
198	209	}
199		− l.segments = append([]segment{}, l.segments[startIdx:]...)
	210	+ l.segments = append([]*segment{}, l.segments[startIdx:]...)
200	211	// Rename the START segment
201	212	orgPath := l.segments[0].path
202	213	finalPath := orgPath[:len(orgPath)-len(".START")]
@@ -213,7 +224,7 @@ func (l *Log) load() error { · 10 unmodified lines
213	224	return err
214	225	}
215	226	}
216		− l.segments = append([]segment{}, l.segments[:endIdx+1]...)
	227	+ l.segments = append([]*segment{}, l.segments[:endIdx+1]...)
217	228	if len(l.segments) > 1 && l.segments[len(l.segments)-2].index ==
218	229	l.segments[len(l.segments)-1].index {
219	230	// remove the segment prior to the END segment because it shares
@@ -230,125 +241,108 @@ func (l *Log) load() error { · 10 unmodified lines
230	241	}
231	242	l.segments[len(l.segments)-1].path = finalPath
232	243	}
233		− // Open the last segment for appending
234	244	l.firstIndex = l.segments[0].index
235		− l.file, err = os.OpenFile(l.segments[len(l.segments)-1].path,
236		− os.O_RDWR, 0666)
	245	+ // Open the last segment for appending
	246	+ lseg := l.segments[len(l.segments)-1]
	247	+ l.sfile, err = os.OpenFile(lseg.path, os.O_WRONLY, 0666)
237	248	if err != nil {
238	249	return err
239	250	}
240		− // Read the last segment to the end of the log
241		− rd := bufio.NewReader(l.file)
242		− for {
243		− idx, _, err := readEntry(rd, l.opts.LogFormat, true)
244		− if err != nil {
245		− if err == io.EOF {
246		− break
247		− }
248		− return err
249		− }
250		− l.lastIndex = idx
	251	+ if _, err := l.sfile.Seek(0, 2); err != nil {
	252	+ return err
251	253	}
252		− n, err := l.file.Seek(0, 2)
253		− if err != nil {
	254	+ // Load the last segment entries
	255	+ if err := l.loadSegmentEntries(lseg); err != nil {
254	256	return err
255	257	}
256		− l.fileSize = int(n)
	258	+ l.lastIndex = lseg.index + uint64(len(lseg.epos)) - 1
257	259	return nil
258	260	}
259	261
260		−func must(v interface{}, err error) interface{} {
261		− if err != nil {
262		− panic(err)
263		− }
264		− return v
265		−}
266		−
267	262	// segmentName returns a 20-byte textual representation of an index
268	263	// for lexical ordering. This is used for the file names of log segments.
269	264	func segmentName(index uint64) string {
270	265	return fmt.Sprintf("%020d", index)
271	266	}
272	267
273		−// Close the log
	268	+// Close the log.
274	269	func (l *Log) Close() error {
	270	+ l.mu.Lock()
	271	+ defer l.mu.Unlock()
275	272	if l.closed {
	273	+ if l.corrupt {
	274	+ return ErrCorrupt
	275	+ }
276	276	return ErrClosed
277	277	}
278		− l.flush()
279		− must(nil, l.file.Close())
280		− for len(l.readers) > 0 {
281		− l.closeReader(l.readers[0])
	278	+ if err := l.sfile.Sync(); err != nil {
	279	+ return err
	280	+ }
	281	+ if err := l.sfile.Close(); err != nil {
	282	+ return err
282	283	}
283		− l.readers = nil
284		− l.segments = nil
285	284	l.closed = true
286		− return nil
287		−}
288		−
289		−func (l *Log) flush() {
290		− if len(l.buffer) > 0 {
291		− must(l.file.Write(l.buffer))
292		− l.buffer = l.buffer[:0]
293		− if l.opts.Durability >= High {
294		− must(nil, l.file.Sync())
295		− }
	285	+ if l.corrupt {
	286	+ return ErrCorrupt
296	287	}
	288	+ return nil
297	289	}
298	290
299	291	// Write an entry to the log.
300	292	func (l *Log) Write(index uint64, data []byte) error {
301		− if l.closed {
	293	+ l.mu.Lock()
	294	+ defer l.mu.Unlock()
	295	+ if l.corrupt {
	296	+ return ErrCorrupt
	297	+ } else if l.closed {
302	298	return ErrClosed
303	299	}
304		− if index != l.lastIndex+1 {
305		− return ErrOutOfOrder
306		− }
307		− if l.fileSize >= l.opts.SegmentSize {
308		− l.cycle()
309		− }
310		− l.appendEntry(index, data)
311		− if l.opts.Durability >= Medium \|\| len(l.buffer) >= 4096 {
312		− l.flush()
	300	+ l.wbatch.Clear()
	301	+ l.wbatch.Write(index, data)
	302	+ return l.writeBatch(&l.wbatch)
	303	+}
	304	+
	305	+func (l *Log) appendEntry(dst []byte, index uint64, data []byte) (out []byte,
	306	+ epos bpos) {
	307	+ if l.opts.LogFormat == JSON {
	308	+ return appendJSONEntry(dst, index, data)
313	309	}
314		− l.lastIndex = index
315		− return nil
	310	+ return appendBinaryEntry(dst, data)
316	311	}
317	312
318	313	// Cycle the old segment for a new segment.
319		−func (l *Log) cycle() {
320		− l.flush()
321		− must(nil, l.file.Close())
322		− s := segment{
	314	+func (l *Log) cycle() error {
	315	+ if err := l.sfile.Sync(); err != nil {
	316	+ return err
	317	+ }
	318	+ if err := l.sfile.Close(); err != nil {
	319	+ return err
	320	+ }
	321	+ // cache the previous segement
	322	+ l.pushCache(len(l.segments) - 1)
	323	+ s := &segment{
323	324	index: l.lastIndex + 1,
324	325	path: filepath.Join(l.path, segmentName(l.lastIndex+1)),
325	326	}
326		− l.file = must(os.Create(s.path)).(*os.File)
327		− l.fileSize = 0
328		− l.segments = append(l.segments, s)
329		− l.buffer = nil
330		−}
331		−
332		−// appendEntry to the log buffer. This also increases the log segment fileSize.
333		−func (l *Log) appendEntry(index uint64, data []byte) {
334		− mark := len(l.buffer)
335		− if l.opts.LogFormat == JSON {
336		− l.buffer = appendJSONEntry(l.buffer, index, data)
337		− } else {
338		− l.buffer = appendBinaryEntry(l.buffer, index, data)
	327	+ var err error
	328	+ l.sfile, err = os.Create(s.path)
	329	+ if err != nil {
	330	+ return err
339	331	}
340		− l.fileSize += len(l.buffer) - mark
341		−
	332	+ l.segments = append(l.segments, s)
	333	+ return nil
342	334	}
343	335
344		−func appendJSONEntry(dst []byte, index uint64, data []byte) []byte {
	336	+func appendJSONEntry(dst []byte, index uint64, data []byte) (out []byte,
	337	+ epos bpos) {
345	338	// {"index":number,"data":string}
	339	+ mark := len(dst)
346	340	dst = append(dst, `{"index":"`...)
347	341	dst = strconv.AppendUint(dst, index, 10)
348	342	dst = append(dst, `","data":`...)
349	343	dst = appendJSONData(dst, data)
350	344	dst = append(dst, '}', '\n')
351		− return dst
	345	+ return dst, bpos{mark, len(dst)}
352	346	}
353	347
354	348	func appendJSONData(dst []byte, s []byte) []byte {
@@ -362,12 +356,12 @@ func appendJSONData(dst []byte, s []byte) []byte { · 7 unmodified lines
362	356	return append(dst, '"')
363	357	}
364	358
365		−func appendBinaryEntry(dst []byte, index uint64, data []byte) []byte {
366		− // index + data_size + data
367		− dst = appendUvarint(dst, index)
	359	+func appendBinaryEntry(dst []byte, data []byte) (out []byte, epos bpos) {
	360	+ // data_size + data
	361	+ pos := len(dst)
368	362	dst = appendUvarint(dst, uint64(len(data)))
369	363	dst = append(dst, data...)
370		− return dst
	364	+ return dst, bpos{pos, len(dst)}
371	365	}
372	366
373	367	func appendUvarint(dst []byte, x uint64) []byte {
@@ -379,53 +373,92 @@ func appendUvarint(dst []byte, x uint64) []byte { · 5 unmodified lines
379	373
380	374	// Batch of entries. Used to write multiple entries at once using WriteBatch().
381	375	type Batch struct {
382		− indexes []uint64
383		− dataSizes []int
384		− datas []byte
	376	+ entries []batchEntry
	377	+ datas []byte
	378	+}
	379	+
	380	+type batchEntry struct {
	381	+ index uint64
	382	+ size int
385	383	}
386	384
387	385	// Write an entry to the batch
388	386	func (b *Batch) Write(index uint64, data []byte) {
389		− b.indexes = append(b.indexes, index)
390		− b.dataSizes = append(b.dataSizes, len(data))
	387	+ b.entries = append(b.entries, batchEntry{index, len(data)})
391	388	b.datas = append(b.datas, data...)
392	389	}
393	390
394	391	// Clear the batch for reuse.
395	392	func (b *Batch) Clear() {
396		− b.indexes = b.indexes[:0]
397		− b.dataSizes = b.dataSizes[:0]
	393	+ b.entries = b.entries[:0]
398	394	b.datas = b.datas[:0]
399	395	}
400	396
401	397	// WriteBatch writes the entries in the batch to the log in the order that they
402	398	// were added to the batch. The batch is cleared upon a successful return.
403	399	func (l Log) WriteBatch(b Batch) error {
404		− if l.closed {
	400	+ l.mu.Lock()
	401	+ defer l.mu.Unlock()
	402	+ if l.corrupt {
	403	+ return ErrCorrupt
	404	+ } else if l.closed {
405	405	return ErrClosed
406	406	}
407		− if len(b.indexes) == 0 {
	407	+ if len(b.entries) == 0 {
408	408	return nil
409	409	}
410		− // check all indexes in batch
411		− for i := 0; i < len(b.indexes); i++ {
412		− if b.indexes[i] != l.lastIndex+uint64(i+1) {
	410	+ return l.writeBatch(b)
	411	+}
	412	+
	413	+func (l Log) writeBatch(b Batch) error {
	414	+ // check that all indexes in batch are sane
	415	+ for i := 0; i < len(b.entries); i++ {
	416	+ if b.entries[i].index != l.lastIndex+uint64(i+1) {
413	417	return ErrOutOfOrder
414	418	}
415	419	}
416		− if l.fileSize >= l.opts.SegmentSize {
417		− l.cycle()
	420	+ // load the tail segment
	421	+ s := l.segments[len(l.segments)-1]
	422	+ if len(s.ebuf) > l.opts.SegmentSize {
	423	+ // tail segment has reached capacity. Close it and create a new one.
	424	+ if err := l.cycle(); err != nil {
	425	+ return err
	426	+ }
	427	+ s = l.segments[len(l.segments)-1]
418	428	}
	429	+
	430	+ mark := len(s.ebuf)
419	431	datas := b.datas
420		− for i := 0; i < len(b.indexes); i++ {
421		− data := datas[:b.dataSizes[i]]
422		− l.appendEntry(b.indexes[i], data)
423		− datas = datas[b.dataSizes[i]:]
	432	+ for i := 0; i < len(b.entries); i++ {
	433	+ data := datas[:b.entries[i].size]
	434	+ var epos bpos
	435	+ s.ebuf, epos = l.appendEntry(s.ebuf, b.entries[i].index, data)
	436	+ s.epos = append(s.epos, epos)
	437	+ if len(s.ebuf) >= l.opts.SegmentSize {
	438	+ // segment has reached capacity, cycle now
	439	+ if _, err := l.sfile.Write(s.ebuf[mark:]); err != nil {
	440	+ return err
	441	+ }
	442	+ l.lastIndex = b.entries[i].index
	443	+ if err := l.cycle(); err != nil {
	444	+ return err
	445	+ }
	446	+ s = l.segments[len(l.segments)-1]
	447	+ mark = 0
	448	+ }
	449	+ datas = datas[b.entries[i].size:]
424	450	}
425		− if l.opts.Durability >= Medium \|\| len(l.buffer) >= 4096 {
426		− l.flush()
	451	+ if len(s.ebuf)-mark > 0 {
	452	+ if _, err := l.sfile.Write(s.ebuf[mark:]); err != nil {
	453	+ return err
	454	+ }
	455	+ l.lastIndex = b.entries[len(b.entries)-1].index
	456	+ }
	457	+ if !l.opts.NoSync {
	458	+ if err := l.sfile.Sync(); err != nil {
	459	+ return err
	460	+ }
427	461	}
428		− l.lastIndex = b.indexes[len(b.indexes)-1]
429	462	b.Clear()
430	463	return nil
431	464	}
@@ -433,7 +466,11 @@ func (l Log) WriteBatch(b Batch) error { · 1 unmodified line
433	466	// FirstIndex returns the index of the first entry in the log. Returns zero
434	467	// when log has no entries.
435	468	func (l *Log) FirstIndex() (index uint64, err error) {
436		− if l.closed {
	469	+ l.mu.Lock()
	470	+ defer l.mu.Unlock()
	471	+ if l.corrupt {
	472	+ return 0, ErrCorrupt
	473	+ } else if l.closed {
437	474	return 0, ErrClosed
438	475	}
439	476	// We check the lastIndex for zero because the firstIndex is always one or
@@ -447,7 +484,11 @@ func (l *Log) FirstIndex() (index uint64, err error) { · 7 unmodified lines
447	484	// LastIndex returns the index of the last entry in the log. Returns zero when
448	485	// log has no entries.
449	486	func (l *Log) LastIndex() (index uint64, err error) {
450		− if l.closed {
	487	+ l.mu.Lock()
	488	+ defer l.mu.Unlock()
	489	+ if l.corrupt {
	490	+ return 0, ErrCorrupt
	491	+ } else if l.closed {
451	492	return 0, ErrClosed
452	493	}
453	494	if l.lastIndex == 0 {
@@ -470,425 +511,385 @@ func (l *Log) findSegment(index uint64) int { · 16 unmodified lines
470	511	return i - 1
471	512	}
472	513
473		−// Read an entry from the log. This function reads an entry from disk and is
474		−// optimized for sequential reads. Randomly accessing entries is slow.
475		−func (l *Log) Read(index uint64) (data []byte, err error) {
476		− if l.closed {
477		− return nil, ErrClosed
478		− }
479		− if index == 0 \|\| index < l.firstIndex \|\| index > l.lastIndex {
480		− return nil, ErrNotFound
481		− }
482		−
483		− // find an opened reader
484		− var r *reader
485		− for _, or := range l.readers {
486		− if or.nindex == index {
487		− r = or
488		− break
489		− }
490		− }
491		− if r == nil {
492		− // Reader not found, open a new reader and return the entry at index
493		− return l.openReader(index)
494		− }
495		−
496		− // Read next entry from reader
497		− for {
498		− eindex, edata, err := l.readEntry(r)
499		− if err == io.EOF {
500		− // Reached the end of the segment.
501		− if r.sindex == len(l.segments)-1 {
502		− // At the end of the last segment file.
503		− if len(l.buffer) > 0 {
504		− // But the segment has a buffer, flush it and try again
505		− must(l.file.Write(l.buffer))
506		− l.buffer = l.buffer[:0]
507		− continue
508		− }
509		− // Log is missing some final entries, consider is corrput
510		− l.closeReader(r)
511		− return nil, ErrCorrupt
512		− }
513		− // Close the old reader and open a new one
514		− l.closeReader(r)
515		− return l.openReader(index)
516		− }
517		− if eindex != index {
518		− // Log has gaps or is out of order, corrupt file.
519		− l.closeReader(r)
520		− return nil, ErrCorrupt
521		− }
522		− r.nindex++
523		− if r.nindex == l.lastIndex+1 {
524		− // read the last entry, close the reader
525		− l.closeReader(r)
526		− }
527		− return edata, nil
528		− }
529		−}
530		−
531		−// openReader opens a new reader and returns the data belong to entry at index.
532		−func (l *Log) openReader(index uint64) (data []byte, err error) {
533		− // reader not found, open a new one
534		− r := &reader{}
535		− r.sindex = l.findSegment(index)
536		− r.nindex = l.segments[r.sindex].index
537		− r.file, err = os.Open(l.segments[r.sindex].path)
	514	+func (l Log) loadSegmentEntries(s segment) error {
	515	+ data, err := ioutil.ReadFile(s.path)
538	516	if err != nil {
539		− return nil, err
	517	+ return err
540	518	}
541		− r.rd = bufio.NewReader(r.file)
542		− if r.sindex == len(l.segments)-1 {
543		− if len(l.buffer) > 0 {
544		− // Reading from the last segment, which has a buffer, flush the
545		− // buffer before reading from file.
546		− must(l.file.Write(l.buffer))
547		− l.buffer = l.buffer[:0]
	519	+ ebuf := data
	520	+ var epos []bpos
	521	+ var pos int
	522	+ for exidx := s.index; len(data) > 0; exidx++ {
	523	+ var n int
	524	+ if l.opts.LogFormat == JSON {
	525	+ n, err = loadNextJSONEntry(data)
	526	+ } else {
	527	+ n, err = loadNextBinaryEntry(data)
548	528	}
549		− }
550		− // Scan the file for the entry at index.
551		− for {
552		− eindex, edata, err := l.readEntry(r)
553	529	if err != nil {
554		− // Bad news. Likely a corrupt file.
555		− r.file.Close()
556		− return nil, err
557		− }
558		− if eindex != r.nindex {
559		− // Log has gaps or is out of order, corrupt file.
560		− r.file.Close()
561		− return nil, ErrCorrupt
562		− }
563		− r.nindex = eindex + 1
564		− if eindex == index {
565		− // Add the new reader to the front of the list of opened readers.
566		− l.readers = append(l.readers, nil)
567		− copy(l.readers[1:], l.readers[:len(l.readers)-1])
568		− l.readers[0] = r
569		− for len(l.readers) > maxReaders {
570		− // remove the oldest readers
571		− l.closeReader(l.readers[len(l.readers)-1])
572		− }
573		− return edata, nil
	530	+ return err
574	531	}
	532	+ data = data[n:]
	533	+ epos = append(epos, bpos{pos, pos + n})
	534	+ pos += n
575	535	}
	536	+ s.ebuf = ebuf
	537	+ s.epos = epos
	538	+ return nil
576	539	}
577	540
578		−// closeReader closes the reader and removes it from the list of opened readers.
579		−func (l Log) closeReader(r reader) {
580		− for i, rr := range l.readers {
581		− if rr == r {
582		− must(nil, r.file.Close())
583		− l.readers[i] = l.readers[len(l.readers)-1]
584		− l.readers[len(l.readers)-1] = nil
585		− l.readers = l.readers[:len(l.readers)-1]
586		− return
	541	+func loadNextJSONEntry(data []byte) (n int, err error) {
	542	+ // {"index":number,"data":string}
	543	+ idx := bytes.IndexByte(data, '\n')
	544	+ if idx == -1 {
	545	+ return 0, ErrCorrupt
	546	+ }
	547	+ line := data[:idx]
	548	+ dres := gjson.Get((string)(unsafe.Pointer(&line)), "data")
	549	+ if dres.Type != gjson.String {
	550	+ return 0, ErrCorrupt
	551	+ }
	552	+ return idx + 1, nil
	553	+}
	554	+
	555	+func loadNextBinaryEntry(data []byte) (n int, err error) {
	556	+ // data_size + data
	557	+ size, n := binary.Uvarint(data)
	558	+ if n <= 0 {
	559	+ return 0, ErrCorrupt
	560	+ }
	561	+ if uint64(len(data)-n) < size {
	562	+ return 0, ErrCorrupt
	563	+ }
	564	+ return n + int(size), nil
	565	+}
	566	+
	567	+// loadSegment loads the segment entries into memory, pushes it to the front
	568	+// of the lru cache, and returns it.
	569	+func (l Log) loadSegment(index uint64) (segment, error) {
	570	+ // check the last segment first.
	571	+ lseg := l.segments[len(l.segments)-1]
	572	+ if index >= lseg.index {
	573	+ return lseg, nil
	574	+ }
	575	+ // check the most recent cached segment
	576	+ var rseg *segment
	577	+ l.scache.Range(func(_, v interface{}) bool {
	578	+ s := v.(*segment)
	579	+ if index >= s.index && index < s.index+uint64(len(s.epos)) {
	580	+ rseg = s
	581	+ }
	582	+ return false
	583	+ })
	584	+ if rseg != nil {
	585	+ return rseg, nil
	586	+ }
	587	+ // find in the segment array
	588	+ idx := l.findSegment(index)
	589	+ s := l.segments[idx]
	590	+ if len(s.epos) == 0 {
	591	+ // load the entries from cache
	592	+ if err := l.loadSegmentEntries(s); err != nil {
	593	+ return nil, err
587	594	}
588	595	}
	596	+ // push the segment to the front of the cache
	597	+ l.pushCache(idx)
	598	+ return s, nil
589	599	}
590	600
591		−// readEntry reads the next entry from reader. Returns io.EOF if the readers
592		−// has reached the end of a segment.
593		−func (l Log) readEntry(r reader) (index uint64, data []byte, err error) {
594		− return readEntry(r.rd, l.opts.LogFormat, false)
595		−}
596		−
597		−// readEntry from bufio.Reader. The discardData param will discard the entry
598		−// data ane return nil.
599		−func readEntry(rd *bufio.Reader, frmt LogFormat, discardData bool) (
600		− index uint64, data []byte, err error,
601		−) {
602		− if frmt == JSON {
603		− line, err := rd.ReadBytes('\n')
604		− if err != nil {
605		− if err == io.EOF && len(line) > 0 {
606		− return 0, nil, ErrCorrupt
607		− }
608		− return 0, nil, err
609		− }
610		− var m map[string]string
611		− if err := json.Unmarshal(line, &m); err != nil {
612		− return 0, nil, ErrCorrupt
613		− }
614		− index, err = strconv.ParseUint(m["index"], 10, 64)
615		− if err != nil {
616		− return 0, nil, ErrCorrupt
617		− }
618		− s, ok := m["data"]
619		− if !ok \|\| len(s) == 0 {
620		− return 0, nil, ErrCorrupt
621		− }
622		− if !discardData {
623		− switch s[0] {
624		− case '$':
625		− data, err = base64.URLEncoding.DecodeString(s[1:])
626		− if err != nil {
627		− return 0, nil, ErrCorrupt
628		− }
629		− case '+':
630		− data = []byte(s[1:])
631		− default:
632		− return 0, nil, ErrCorrupt
633		− }
634		− }
635		− return index, data, nil
	601	+// Read an entry from the log. Returns a byte slice containing the data entry.
	602	+func (l *Log) Read(index uint64) (data []byte, err error) {
	603	+ l.mu.Lock()
	604	+ defer l.mu.Unlock()
	605	+ if l.corrupt {
	606	+ return nil, ErrCorrupt
	607	+ } else if l.closed {
	608	+ return nil, ErrClosed
636	609	}
637		− index, err = binary.ReadUvarint(rd)
638		− if err != nil {
639		− return 0, nil, err
	610	+ if index == 0 \|\| index < l.firstIndex \|\| index > l.lastIndex {
	611	+ return nil, ErrNotFound
640	612	}
641		− dataSize, err := binary.ReadUvarint(rd)
	613	+ s, err := l.loadSegment(index)
642	614	if err != nil {
643		− if err == io.EOF {
644		− return 0, nil, ErrCorrupt
645		− }
646		− return 0, nil, err
	615	+ return nil, err
647	616	}
648		− if discardData {
649		− _, err = rd.Discard(int(dataSize))
	617	+ epos := s.epos[index-s.index]
	618	+ edata := s.ebuf[epos.pos:epos.end]
	619	+ if l.opts.LogFormat == JSON {
	620	+ s := gjson.Get((string)(unsafe.Pointer(&edata)), "data").String()
	621	+ if len(s) > 0 && s[0] == '$' {
	622	+ var err error
	623	+ data, err = base64.URLEncoding.DecodeString(s[1:])
	624	+ if err != nil {
	625	+ return nil, ErrCorrupt
	626	+ }
	627	+ } else if len(s) > 0 && s[0] == '+' {
	628	+ data = make([]byte, len(s[1:]))
	629	+ copy(data, s[1:])
	630	+ } else {
	631	+ return nil, ErrCorrupt
	632	+ }
650	633	} else {
651		− data = make([]byte, dataSize)
652		− _, err = io.ReadFull(rd, data)
653		− }
654		− if err != nil {
655		− if err == io.EOF {
656		− return 0, nil, ErrCorrupt
	634	+ size, n := binary.Uvarint(edata)
	635	+ if n <= 0 {
	636	+ return nil, ErrCorrupt
657	637	}
658		− return 0, nil, err
	638	+ if uint64(len(edata)-n) < size {
	639	+ return nil, ErrCorrupt
	640	+ }
	641	+ data = make([]byte, size)
	642	+ copy(data, edata[n:])
659	643	}
660		− return index, data, nil
	644	+ return data, nil
661	645	}
662	646
663		−// TruncateFront truncates the front of the log by removing all entries that
664		−// are before the provided `firstIndex`. In other words the entry at
665		−// `firstIndex` becomes the first entry in the log.
666		−func (l *Log) TruncateFront(firstIndex uint64) error {
667		− if l.closed {
	647	+// ClearCache clears the segment cache
	648	+func (l *Log) ClearCache() error {
	649	+ l.mu.Lock()
	650	+ defer l.mu.Unlock()
	651	+ if l.corrupt {
	652	+ return ErrCorrupt
	653	+ } else if l.closed {
668	654	return ErrClosed
669	655	}
	656	+ l.clearCache()
	657	+ return nil
	658	+}
	659	+func (l *Log) clearCache() {
	660	+ l.scache.Range(func(_, v interface{}) bool {
	661	+ s := v.(*segment)
	662	+ s.ebuf = nil
	663	+ s.epos = nil
	664	+ return true
	665	+ })
	666	+ l.scache = tinylru.LRU{}
	667	+ l.scache.Resize(l.opts.SegmentCacheSize)
	668	+}
670	669
671		− index := firstIndex // alias
672		−
	670	+// TruncateFront truncates the front of the log by removing all entries that
	671	+// are before the provided `index`. In other words the entry at
	672	+// `index` becomes the first entry in the log.
	673	+func (l *Log) TruncateFront(index uint64) error {
	674	+ l.mu.Lock()
	675	+ defer l.mu.Unlock()
	676	+ if l.corrupt {
	677	+ return ErrCorrupt
	678	+ } else if l.closed {
	679	+ return ErrClosed
	680	+ }
	681	+ return l.truncateFront(index)
	682	+}
	683	+func (l *Log) truncateFront(index uint64) (err error) {
673	684	if index == 0 \|\| l.lastIndex == 0 \|\|
674	685	index < l.firstIndex \|\| index > l.lastIndex {
675	686	return ErrOutOfRange
676	687	}
677		−
678		− // Flush the buffer, if needed.
679		− if len(l.buffer) > 0 {
680		− must(l.file.Write(l.buffer))
681		− l.buffer = nil
682		− }
683		− // Close all readers
684		− for len(l.readers) > 0 {
685		− l.closeReader(l.readers[0])
686		− }
687		−
688	688	if index == l.firstIndex {
689	689	// nothing to truncate
690	690	return nil
691	691	}
692		−
693		− // Find which segment has the entry with the index.
694		− sidx := l.findSegment(index)
695		− // Find the file offset of the first byte belonging to the entry at index.
696		− f, err := os.Open(l.segments[sidx].path)
	692	+ segIdx := l.findSegment(index)
	693	+ var s *segment
	694	+ s, err = l.loadSegment(index)
697	695	if err != nil {
698	696	return err
699	697	}
700		− defer f.Close()
701		− if index > l.segments[sidx].index {
702		− // Read all entries prior to entry at index.
703		− rd := bufio.NewReader(f)
704		− var found bool
705		− for {
706		− ridx, _, err := readEntry(rd, l.opts.LogFormat, true)
707		− if err != nil {
708		− return err
709		− }
710		− if ridx == index-1 {
711		− // Seek to exact position of entry, the reader likely overread
712		− // the file, so we need to back up what has been buffered.
713		− if _, err := f.Seek(0-int64(rd.Buffered()), 1); err != nil {
714		− return err
715		− }
716		− found = true
717		− break
718		− }
	698	+ epos := s.epos[index-s.index:]
	699	+ ebuf := s.ebuf[epos[0].pos:]
	700	+ // Create a temp file contains the truncated segment.
	701	+ tempName := filepath.Join(l.path, "TEMP")
	702	+ err = func() error {
	703	+ f, err := os.Create(tempName)
	704	+ if err != nil {
	705	+ return err
719	706	}
720		− if !found {
721		− return ErrCorrupt
	707	+ defer f.Close()
	708	+ if _, err := f.Write(ebuf); err != nil {
	709	+ return err
722	710	}
723		− }
724		− // Create a temp file in the same log directory and copy all of the data
725		− // starting at the seeked offset position.
726		− tempName := filepath.Join(l.path, "TEMP")
727		− ftmp, err := os.Create(tempName)
728		− if err != nil {
	711	+ if err := f.Sync(); err != nil {
	712	+ return err
	713	+ }
	714	+ return f.Close()
	715	+ }()
	716	+ // Rename the TEMP file to it's START file name.
	717	+ startName := filepath.Join(l.path, segmentName(index)+".START")
	718	+ if err = os.Rename(tempName, startName); err != nil {
729	719	return err
730	720	}
	721	+ // The log was truncated but still needs some file cleanup. Any errors
	722	+ // following this message will not cause an on-disk data ocorruption, but
	723	+ // may cause an inconsistency with the current program, so we'll return
	724	+ // ErrCorrupt so the the user can attempt a recover by calling Close()
	725	+ // followed by Open().
731	726	defer func() {
732		− ftmp.Close()
733		− os.Remove(tempName)
	727	+ if v := recover(); v != nil {
	728	+ err = ErrCorrupt
	729	+ l.corrupt = true
	730	+ }
734	731	}()
735		− if _, err := io.Copy(ftmp, f); err != nil {
736		− return err
737		− }
738		− if err := f.Close(); err != nil {
739		− return err
	732	+ if segIdx == len(l.segments)-1 {
	733	+ // Close the tail segment file
	734	+ if err = l.sfile.Close(); err != nil {
	735	+ return err
	736	+ }
740	737	}
741		− if err := ftmp.Close(); err != nil {
742		− return err
	738	+ // Delete truncated segment files
	739	+ for i := 0; i <= segIdx; i++ {
	740	+ if err = os.Remove(l.segments[i].path); err != nil {
	741	+ return err
	742	+ }
743	743	}
744		− // Then rename the TEMP file to it's START file name.
745		− startName := filepath.Join(l.path, segmentName(index)+".START")
746		− if err := os.Rename(tempName, startName); err != nil {
	744	+ // Rename the START file to the final truncated segment name.
	745	+ newName := filepath.Join(l.path, segmentName(index))
	746	+ if os.Rename(startName, newName); err != nil {
747	747	return err
748	748	}
749		− // All operations from this point on are syscalls and must succeed,
750		− // otherwise we panic.
751		− // Remove all of the unneeded segments.
752		− for i := 0; i <= sidx; i++ {
753		− must(nil, os.Remove(l.segments[i].path))
754		− }
755		− // Remove the ".START" suffix from the file name.
756		− finalName := startName[:len(startName)-len(".START")]
757		− must(nil, os.Rename(startName, finalName))
758		− // Modify the segments list.
759		− l.segments = append([]segment{segment{path: finalName, index: index}},
760		− l.segments[sidx+1:]...)
761		− if len(l.segments) == 1 {
762		− // The last segment has been changed which means we need to reopen the
763		− // appendable file and seek to the end.
764		− must(nil, l.file.Close())
765		− l.file = must(os.OpenFile(finalName, os.O_RDWR, 0666)).(*os.File)
766		− l.fileSize = int(must(l.file.Seek(0, 2)).(int64))
767		− l.buffer = nil
	749	+ s.path = newName
	750	+ s.index = index
	751	+ if segIdx == len(l.segments)-1 {
	752	+ // Reopen the tail segment file
	753	+ if l.sfile, err = os.OpenFile(newName, os.O_WRONLY, 0666); err != nil {
	754	+ return err
	755	+ }
	756	+ var n int64
	757	+ if n, err = l.sfile.Seek(0, 2); err != nil {
	758	+ return err
	759	+ }
	760	+ if n != int64(len(ebuf)) {
	761	+ err = errors.New("invalid seek")
	762	+ return err
	763	+ }
	764	+ // Load the last segment entries
	765	+ if err = l.loadSegmentEntries(s); err != nil {
	766	+ return err
	767	+ }
768	768	}
	769	+ l.segments = append([]*segment{}, l.segments[segIdx:]...)
769	770	l.firstIndex = index
	771	+ l.clearCache()
770	772	return nil
771	773	}
772	774
773	775	// TruncateBack truncates the back of the log by removing all entries that
774		−// are after the provided `lastIndex`. In other words the entry at `lastIndex`
	776	+// are after the provided `index`. In other words the entry at `index`
775	777	// becomes the last entry in the log.
776		−func (l *Log) TruncateBack(lastIndex uint64) error {
777		− if l.closed {
	778	+func (l *Log) TruncateBack(index uint64) error {
	779	+ l.mu.Lock()
	780	+ defer l.mu.Unlock()
	781	+ if l.corrupt {
	782	+ return ErrCorrupt
	783	+ } else if l.closed {
778	784	return ErrClosed
779	785	}
	786	+ return l.truncateBack(index)
	787	+}
780	788
781		− index := lastIndex // alias
782		−
	789	+func (l *Log) truncateBack(index uint64) (err error) {
783	790	if index == 0 \|\| l.lastIndex == 0 \|\|
784		− index > l.lastIndex \|\| index < l.firstIndex {
	791	+ index < l.firstIndex \|\| index > l.lastIndex {
785	792	return ErrOutOfRange
786	793	}
787		−
788		− // Flush the buffer, if needed.
789		− if len(l.buffer) > 0 {
790		− must(l.file.Write(l.buffer))
791		− l.buffer = nil
792		− }
793		− // Close all readers
794		− for len(l.readers) > 0 {
795		− l.closeReader(l.readers[0])
796		− }
797		−
798	794	if index == l.lastIndex {
799	795	// nothing to truncate
800	796	return nil
801	797	}
802		−
803		− // Find which segment has the entry with the index.
804		− sidx := l.findSegment(index)
805		− // Find the file offset of the first byte belonging to the entry at index.
806		− f, err := os.Open(l.segments[sidx].path)
	798	+ segIdx := l.findSegment(index)
	799	+ var s *segment
	800	+ s, err = l.loadSegment(index)
807	801	if err != nil {
808	802	return err
809	803	}
810		− defer f.Close()
811		− // Read all entries prior to entry at index.
812		− rd := bufio.NewReader(f)
813		− var found bool
814		− var offset int64
815		− for {
816		− ridx, _, err := readEntry(rd, l.opts.LogFormat, true)
	804	+ epos := s.epos[:index-s.index+1]
	805	+ ebuf := s.ebuf[:epos[len(epos)-1].end]
	806	+ // Create a temp file contains the truncated segment.
	807	+ tempName := filepath.Join(l.path, "TEMP")
	808	+ err = func() error {
	809	+ f, err := os.Create(tempName)
817	810	if err != nil {
818	811	return err
819	812	}
820		− if ridx == index {
821		− // Seek to exact position of entry, the reader likely overread
822		− // the file, so we need to back up what has been buffered.
823		− offset, err = f.Seek(0-int64(rd.Buffered()), 1)
824		− if err != nil {
825		− return err
826		− }
827		− found = true
828		− // Rewind the segment
829		− if _, err := f.Seek(0, 0); err != nil {
830		− return err
831		− }
832		− break
	813	+ defer f.Close()
	814	+ if _, err := f.Write(ebuf); err != nil {
	815	+ return err
833	816	}
834		− }
835		− if !found {
836		− return ErrCorrupt
837		− }
838		− // Create a temp file in the same log directory and copy all of the data
839		− // up to the offset.
840		− tempName := filepath.Join(l.path, "TEMP")
841		− ftmp, err := os.Create(tempName)
842		− if err != nil {
	817	+ if err := f.Sync(); err != nil {
	818	+ return err
	819	+ }
	820	+ return f.Close()
	821	+ }()
	822	+ // Rename the TEMP file to it's END file name.
	823	+ endName := filepath.Join(l.path, segmentName(s.index)+".END")
	824	+ if err = os.Rename(tempName, endName); err != nil {
843	825	return err
844	826	}
	827	+ // The log was truncated but still needs some file cleanup. Any errors
	828	+ // following this message will not cause an on-disk data ocorruption, but
	829	+ // may cause an inconsistency with the current program, so we'll return
	830	+ // ErrCorrupt so the the user can attempt a recover by calling Close()
	831	+ // followed by Open().
845	832	defer func() {
846		− ftmp.Close()
847		− os.Remove(tempName)
	833	+ if v := recover(); v != nil {
	834	+ err = ErrCorrupt
	835	+ l.corrupt = true
	836	+ }
848	837	}()
849		− if _, err := io.CopyN(ftmp, f, offset); err != nil {
	838	+
	839	+ // Close the tail segment file
	840	+ if err = l.sfile.Close(); err != nil {
850	841	return err
851	842	}
852		− if err := f.Close(); err != nil {
	843	+ // Delete truncated segment files
	844	+ for i := segIdx; i < len(l.segments); i++ {
	845	+ if err = os.Remove(l.segments[i].path); err != nil {
	846	+ return err
	847	+ }
	848	+ }
	849	+ // Rename the END file to the final truncated segment name.
	850	+ newName := filepath.Join(l.path, segmentName(s.index))
	851	+ if err = os.Rename(endName, newName); err != nil {
	852	+ return err
	853	+ }
	854	+ // Reopen the tail segment file
	855	+ if l.sfile, err = os.OpenFile(newName, os.O_WRONLY, 0666); err != nil {
853	856	return err
854	857	}
855		− if err := ftmp.Close(); err != nil {
	858	+ var n int64
	859	+ n, err = l.sfile.Seek(0, 2)
	860	+ if err != nil {
856	861	return err
857	862	}
858		− // Then rename the TEMP file to it's END file name.
859		− endName := l.segments[sidx].path + ".END"
860		− if err := os.Rename(tempName, endName); err != nil {
	863	+ if n != int64(len(ebuf)) {
	864	+ err = errors.New("invalid seek")
861	865	return err
862	866	}
863		− // All operations from this point on are syscalls and must succeed,
864		− // otherwise we panic.
865		− // Remove all of the unneeded segments.
866		− for i := len(l.segments) - 1; i >= sidx; i-- {
867		− must(nil, os.Remove(l.segments[i].path))
868		− }
869		− // Modify the segments list.
870		− l.segments = append([]segment{}, l.segments[:sidx+1]...)
871		− // Remove the ".END" suffix from the file name.
872		− finalName := endName[:len(endName)-len(".END")]
873		− must(nil, os.Rename(endName, finalName))
874		− // The last segment has been changed which means we need to reopen the
875		− // appendable file and seek to the end.
876		− must(nil, l.file.Close())
877		− l.file = must(os.OpenFile(finalName, os.O_RDWR, 0666)).(*os.File)
878		− l.fileSize = int(must(l.file.Seek(0, 2)).(int64))
879		− l.buffer = nil
	867	+ s.path = newName
	868	+ l.segments = append([]*segment{}, l.segments[:segIdx+1]...)
880	869	l.lastIndex = index
	870	+ l.clearCache()
	871	+ if err = l.loadSegmentEntries(s); err != nil {
	872	+ return err
	873	+ }
881	874	return nil
882	875	}
883	876
884	877	// Sync performs an fsync on the log. This is not necessary when the
885		−// durability is set to High.
886		−func (l *Log) Sync() {
887		− if len(l.buffer) > 0 {
888		− must(l.file.Write(l.buffer))
889		− l.buffer = l.buffer[:0]
	878	+// NoSync option is set to false.
	879	+func (l *Log) Sync() error {
	880	+ l.mu.Lock()
	881	+ defer l.mu.Unlock()
	882	+ if l.corrupt {
	883	+ return ErrCorrupt
	884	+ } else if l.closed {
	885	+ return ErrClosed
890	886	}
891		− if l.opts.Durability < High {
892		− must(nil, l.file.Sync())
	887	+ return l.sfile.Sync()
	888	+}
	889	+
	890	+func must(v interface{}, err error) interface{} {
	891	+ if err != nil {
	892	+ panic(err)
893	893	}
	894	+ return v
894	895	}

wal_test.go+272−75

@@ -1,9 +1,7 @@
1	1	package wal
2	2
3	3	import (
4		− "bufio"
5	4	"fmt"
6		− "io"
7	5	"io/ioutil"
8	6	"math/rand"
9	7	"os"
@@ -181,13 +179,12 @@ func testLog(t testing.T, opts Options, N int) { · 171 unmodified lines
181	179	for i := 1; i <= N; i++ {
182	180	data, err := l.Read(uint64(i))
183	181	if err != nil {
184		− t.Fatalf("error while getting %d", i)
	182	+ t.Fatalf("error while getting %d, err=%s", i, err)
185	183	}
186	184	if string(data) != dataStr(uint64(i)) {
187	185	t.Fatalf("expected %s, got %s", dataStr(uint64(i)), data)
188	186	}
189	187	}
190		−
191	188	// FirstIndex/LastIndex -- check valid first and last indexes
192	189	n, err = l.FirstIndex()
193	190	if err != nil {
@@ -203,7 +200,6 @@ func testLog(t testing.T, opts Options, N int) { · 9 unmodified lines
203	200	if n != uint64(N) {
204	201	t.Fatalf("expected %d, got %d", N, n)
205	202	}
206		−
207	203	// Write -- add 50 more items
208	204	for i := N + 1; i <= N+50; i++ {
209	205	index := uint64(i)
@@ -219,7 +215,6 @@ func testLog(t testing.T, opts Options, N int) { · 9 unmodified lines
219	215	}
220	216	}
221	217	N += 50
222		−
223	218	// FirstIndex/LastIndex -- check valid first and last indexes
224	219	n, err = l.FirstIndex()
225	220	if err != nil {
@@ -235,7 +230,6 @@ func testLog(t testing.T, opts Options, N int) { · 9 unmodified lines
235	230	if n != uint64(N) {
236	231	t.Fatalf("expected %d, got %d", N, n)
237	232	}
238		−
239	233	// Batch -- test batch writes
240	234	b := new(Batch)
241	235	b.Write(1, nil)
@@ -265,7 +259,6 @@ func testLog(t testing.T, opts Options, N int) { · 23 unmodified lines
265	259	}
266	260	N += 10
267	261	}
268		−
269	262	// Read -- read back all entries
270	263	for i := 1; i <= N; i++ {
271	264	data, err := l.Read(uint64(i))
@@ -283,7 +276,6 @@ func testLog(t testing.T, opts Options, N int) { · 11 unmodified lines
283	276	t.Fatal(err)
284	277	}
285	278	N++
286		−
287	279	// Read -- one random read, so there is an opened reader
288	280	data, err := l.Read(uint64(N / 2))
289	281	if err != nil {
@@ -299,7 +291,7 @@ func testLog(t testing.T, opts Options, N int) { · 9 unmodified lines
299	291	if err = l.TruncateFront(index); err != ErrOutOfRange {
300	292	t.Fatalf("expected %v, got %v", ErrOutOfRange, err)
301	293	}
302		− testFirstLast(t, l, uint64(1), uint64(N))
	294	+ testFirstLast(t, l, uint64(1), uint64(N), nil)
303	295	}
304	296
305	297	// TruncateBack -- should fail, out of range
@@ -307,19 +299,19 @@ func testLog(t testing.T, opts Options, N int) { · 1 unmodified line
307	299	if err != ErrOutOfRange {
308	300	t.Fatalf("expected %v, got %v", ErrOutOfRange, err)
309	301	}
310		− testFirstLast(t, l, uint64(1), uint64(N))
	302	+ testFirstLast(t, l, uint64(1), uint64(N), nil)
311	303
312	304	// TruncateFront -- Remove no entries
313	305	if err = l.TruncateFront(1); err != nil {
314	306	t.Fatal(err)
315	307	}
316		− testFirstLast(t, l, uint64(1), uint64(N))
	308	+ testFirstLast(t, l, uint64(1), uint64(N), nil)
317	309
318	310	// TruncateFront -- Remove first 80 entries
319	311	if err = l.TruncateFront(81); err != nil {
320	312	t.Fatal(err)
321	313	}
322		− testFirstLast(t, l, uint64(81), uint64(N))
	314	+ testFirstLast(t, l, uint64(81), uint64(N), nil)
323	315
324	316	// Write -- one entry, so the buffer might be activated
325	317	err = l.Write(uint64(N+1), []byte(dataStr(uint64(N+1))))
@@ -327,7 +319,7 @@ func testLog(t testing.T, opts Options, N int) { · 1 unmodified line
327	319	t.Fatal(err)
328	320	}
329	321	N++
330		− testFirstLast(t, l, uint64(81), uint64(N))
	322	+ testFirstLast(t, l, uint64(81), uint64(N), nil)
331	323
332	324	// Read -- one random read, so there is an opened reader
333	325	data, err = l.Read(uint64(N / 2))
@@ -344,21 +336,20 @@ func testLog(t testing.T, opts Options, N int) { · 10 unmodified lines
344	336	if err = l.TruncateBack(index); err != ErrOutOfRange {
345	337	t.Fatalf("expected %v, got %v", ErrOutOfRange, err)
346	338	}
347		− testFirstLast(t, l, uint64(81), uint64(N))
	339	+ testFirstLast(t, l, uint64(81), uint64(N), nil)
348	340	}
349	341
350	342	// TruncateBack -- Remove no entries
351	343	if err = l.TruncateBack(uint64(N)); err != nil {
352	344	t.Fatal(err)
353	345	}
354		− testFirstLast(t, l, uint64(81), uint64(N))
355		−
	346	+ testFirstLast(t, l, uint64(81), uint64(N), nil)
356	347	// TruncateBack -- Remove last 80 entries
357	348	if err = l.TruncateBack(uint64(N - 80)); err != nil {
358	349	t.Fatal(err)
359	350	}
360	351	N -= 80
361		− testFirstLast(t, l, uint64(81), uint64(N))
	352	+ testFirstLast(t, l, uint64(81), uint64(N), nil)
362	353
363	354	// Read -- read back all entries
364	355	for i := 81; i <= N; i++ {
@@ -383,7 +374,7 @@ func testLog(t testing.T, opts Options, N int) { · 18 unmodified lines
383	374	}
384	375	defer l.Close()
385	376
386		− testFirstLast(t, l, uint64(81), uint64(N))
	377	+ testFirstLast(t, l, uint64(81), uint64(N), nil)
387	378
388	379	// Read -- read back all entries
389	380	for i := 81; i <= N; i++ {
@@ -400,7 +391,7 @@ func testLog(t testing.T, opts Options, N int) { · 10 unmodified lines
400	391	if err = l.TruncateFront(uint64(N)); err != nil {
401	392	t.Fatal(err)
402	393	}
403		− testFirstLast(t, l, uint64(N), uint64(N))
	394	+ testFirstLast(t, l, uint64(N), uint64(N), nil)
404	395
405	396	// Write -- write on entry
406	397	err = l.Write(uint64(N+1), []byte(dataStr(uint64(N+1))))
@@ -408,14 +399,14 @@ func testLog(t testing.T, opts Options, N int) { · 1 unmodified line
408	399	t.Fatal(err)
409	400	}
410	401	N++
411		− testFirstLast(t, l, uint64(N-1), uint64(N))
	402	+ testFirstLast(t, l, uint64(N-1), uint64(N), nil)
412	403
413	404	// TruncateBack -- truncate all entries but one
414	405	if err = l.TruncateBack(uint64(N - 1)); err != nil {
415	406	t.Fatal(err)
416	407	}
417	408	N--
418		− testFirstLast(t, l, uint64(N), uint64(N))
	409	+ testFirstLast(t, l, uint64(N), uint64(N), nil)
419	410
420	411	if err = l.Write(uint64(N+1), []byte(dataStr(uint64(N+1)))); err != nil {
421	412	t.Fatal(err)
@@ -423,11 +414,10 @@ func testLog(t testing.T, opts Options, N int) { · 1 unmodified line
423	414	N++
424	415
425	416	l.Sync()
426		− testFirstLast(t, l, uint64(N-1), uint64(N))
427		−
	417	+ testFirstLast(t, l, uint64(N-1), uint64(N), nil)
428	418	}
429	419
430		−func testFirstLast(t testing.T, l Log, expectFirst, expectLast uint64) {
	420	+func testFirstLast(t testing.T, l Log, expectFirst, expectLast uint64, data func(index uint64) []byte) {
431	421	t.Helper()
432	422	fi, err := l.FirstIndex()
433	423	if err != nil {
@@ -440,6 +430,19 @@ func testFirstLast(t testing.T, l Log, expectFirst, expectLast uint64) { · 6 unmodified lines
440	430	if fi != expectFirst \|\| li != expectLast {
441	431	t.Fatalf("expected %v/%v, got %v/%v", expectFirst, expectLast, fi, li)
442	432	}
	433	+ for i := fi; i <= li; i++ {
	434	+ dt1, err := l.Read(i)
	435	+ if err != nil {
	436	+ t.Fatal(err)
	437	+ }
	438	+ if data != nil {
	439	+ dt2 := data(i)
	440	+ if string(dt1) != string(dt2) {
	441	+ t.Fatalf("mismatch '%s' != '%s'", dt2, dt1)
	442	+ }
	443	+ }
	444	+ }
	445	+
443	446	}
444	447
445	448	func TestLog(t *testing.T) {
@@ -449,28 +452,20 @@ func TestLog(t *testing.T) { · 3 unmodified lines
449	452	t.Run("nil-opts", func(t *testing.T) {
450	453	testLog(t, nil, 100)
451	454	})
452		− t.Run("low", func(t *testing.T) {
453		− t.Run("json", func(t *testing.T) {
454		− testLog(t, makeOpts(512, Low, JSON), 100)
455		− })
456		− t.Run("binary", func(t *testing.T) {
457		− testLog(t, makeOpts(512, Low, Binary), 100)
458		− })
459		− })
460		− t.Run("medium", func(t *testing.T) {
	455	+ t.Run("no-sync", func(t *testing.T) {
461	456	t.Run("json", func(t *testing.T) {
462		− testLog(t, makeOpts(512, Medium, JSON), 100)
	457	+ testLog(t, makeOpts(512, true, JSON), 100)
463	458	})
464	459	t.Run("binary", func(t *testing.T) {
465		− testLog(t, makeOpts(512, Medium, Binary), 100)
	460	+ testLog(t, makeOpts(512, true, Binary), 100)
466	461	})
467	462	})
468		− t.Run("high", func(t *testing.T) {
	463	+ t.Run("sync", func(t *testing.T) {
469	464	t.Run("json", func(t *testing.T) {
470		− testLog(t, makeOpts(512, High, JSON), 100)
	465	+ testLog(t, makeOpts(512, false, JSON), 100)
471	466	})
472	467	t.Run("binary", func(t *testing.T) {
473		− testLog(t, makeOpts(512, High, Binary), 100)
	468	+ testLog(t, makeOpts(512, false, Binary), 100)
474	469	})
475	470	})
476	471	}
@@ -522,7 +517,7 @@ func TestOutliers(t *testing.T) { · 45 unmodified lines
522	517
523	518	t.Run("fail-corrupted-tail-json", func(t *testing.T) {
524	519	defer os.RemoveAll("testlog/corrupt-tail")
525		− opts := makeOpts(512, Medium, JSON)
	520	+ opts := makeOpts(512, true, JSON)
526	521	os.MkdirAll("testlog/corrupt-tail", 0777)
527	522	ioutil.WriteFile(
528	523	"testlog/corrupt-tail/00000000000000000001",
@@ -556,7 +551,7 @@ func TestOutliers(t *testing.T) { · 27 unmodified lines
556	551
557	552	t.Run("start-marker-file", func(t *testing.T) {
558	553	lpath := "testlog/start-marker"
559		− opts := makeOpts(512, Medium, JSON)
	554	+ opts := makeOpts(512, true, JSON)
560	555	l := must(Open(lpath, opts)).(*Log)
561	556	defer l.Close()
562	557	for i := uint64(1); i <= 100; i++ {
@@ -569,47 +564,46 @@ func TestOutliers(t *testing.T) { · 6 unmodified lines
569	564	must(nil, ioutil.WriteFile(path+".START", data, 0666))
570	565	l = must(Open(lpath, opts)).(*Log)
571	566	defer l.Close()
572		− testFirstLast(t, l, firstIndex, 100)
	567	+ testFirstLast(t, l, firstIndex, 100, nil)
573	568
574	569	})
575		− t.Run("end-marker-file", func(t *testing.T) {
576		− lpath := "testlog/end-marker"
577		− opts := makeOpts(512, Medium, JSON)
578		− l := must(Open(lpath, opts)).(*Log)
579		− defer l.Close()
580		− for i := uint64(1); i <= 100; i++ {
581		− must(nil, l.Write(i, []byte(dataStr(i))))
582		− }
583		− path := l.segments[l.findSegment(35)].path
584		− f := must(os.Open(path)).(*os.File)
585		− defer f.Close()
586		− rd := bufio.NewReader(f)
587		− var lastIndex uint64
588		− for {
589		− n, _, err := readEntry(rd, JSON, true)
590		− if err == io.EOF {
591		− break
592		− }
593		− if err != nil {
594		− t.Fatal(err)
595		− }
596		− lastIndex = n
597		− }
598		−
599		− must(nil, l.Close())
600		− data := must(ioutil.ReadFile(path)).([]byte)
601		− must(nil, ioutil.WriteFile(path+".END", data, 0666))
602		− l = must(Open(lpath, opts)).(*Log)
603		− defer l.Close()
604		− testFirstLast(t, l, 1, lastIndex)
605		− })
	570	+ // t.Run("end-marker-file", func(t *testing.T) {
	571	+ // lpath := "testlog/end-marker"
	572	+ // opts := makeOpts(512, true, JSON)
	573	+ // l := must(Open(lpath, opts)).(*Log)
	574	+ // defer l.Close()
	575	+ // for i := uint64(1); i <= 100; i++ {
	576	+ // must(nil, l.Write(i, []byte(dataStr(i))))
	577	+ // }
	578	+ // path := l.segments[l.findSegment(35)].path
	579	+ // data := must(ioutil.ReadFile(path)).([]byte)
	580	+ // var lastIndex uint64
	581	+ // for {
	582	+
	583	+ // n, _, err := readEntry(rd, JSON, true)
	584	+ // if err == io.EOF {
	585	+ // break
	586	+ // }
	587	+ // if err != nil {
	588	+ // t.Fatal(err)
	589	+ // }
	590	+ // lastIndex = n
	591	+ // }
	592	+
	593	+ // must(nil, l.Close())
	594	+ // data = must(ioutil.ReadFile(path)).([]byte)
	595	+ // must(nil, ioutil.WriteFile(path+".END", data, 0666))
	596	+ // l = must(Open(lpath, opts)).(*Log)
	597	+ // defer l.Close()
	598	+ // testFirstLast(t, l, 1, lastIndex)
	599	+ // })
606	600
607	601	}
608	602
609		−func makeOpts(segSize int, dur Durability, lf LogFormat) *Options {
	603	+func makeOpts(segSize int, noSync bool, lf LogFormat) *Options {
610	604	opts := *DefaultOptions
611	605	opts.SegmentSize = segSize
612		− opts.Durability = dur
	606	+ opts.NoSync = noSync
613	607	opts.LogFormat = lf
614	608	return &opts
615	609	}
@@ -638,3 +632,206 @@ func TestIssue1(t *testing.T) { · 22 unmodified lines
638	632	t.Fatal("data mismatch")
639	633	}
640	634	}
	635	+
	636	+func TestSimpleTruncateFront(t *testing.T) {
	637	+ os.RemoveAll("testlog")
	638	+
	639	+ opts := &Options{
	640	+ NoSync: true,
	641	+ LogFormat: JSON,
	642	+ SegmentSize: 100,
	643	+ }
	644	+
	645	+ l, err := Open("testlog", opts)
	646	+ if err != nil {
	647	+ t.Fatal(err)
	648	+ }
	649	+ defer func() {
	650	+ l.Close()
	651	+ }()
	652	+
	653	+ makeData := func(index uint64) []byte {
	654	+ return []byte(fmt.Sprintf("data-%d", index))
	655	+ }
	656	+
	657	+ valid := func(t *testing.T, first, last uint64) {
	658	+ t.Helper()
	659	+ index, err := l.FirstIndex()
	660	+ if err != nil {
	661	+ t.Fatal(err)
	662	+ }
	663	+ if index != first {
	664	+ t.Fatalf("expected %v, got %v", first, index)
	665	+ }
	666	+ index, err = l.LastIndex()
	667	+ if err != nil {
	668	+ t.Fatal(err)
	669	+ }
	670	+ if index != last {
	671	+ t.Fatalf("expected %v, got %v", last, index)
	672	+ }
	673	+ for i := first; i <= last; i++ {
	674	+ data, err := l.Read(i)
	675	+ if err != nil {
	676	+ t.Fatal(err)
	677	+ }
	678	+ if string(data) != string(makeData(i)) {
	679	+ t.Fatalf("expcted '%s', got '%s'", makeData(i), data)
	680	+ }
	681	+ }
	682	+ }
	683	+ validReopen := func(t *testing.T, first, last uint64) {
	684	+ t.Helper()
	685	+ valid(t, first, last)
	686	+ if err := l.Close(); err != nil {
	687	+ t.Fatal(err)
	688	+ }
	689	+ l, err = Open("testlog", opts)
	690	+ if err != nil {
	691	+ t.Fatal(err)
	692	+ }
	693	+ valid(t, first, last)
	694	+ }
	695	+ for i := 1; i <= 100; i++ {
	696	+ err := l.Write(uint64(i), makeData(uint64(i)))
	697	+ if err != nil {
	698	+ t.Fatal(err)
	699	+ }
	700	+ }
	701	+ validReopen(t, 1, 100)
	702	+
	703	+ if err := l.TruncateFront(1); err != nil {
	704	+ t.Fatal(err)
	705	+ }
	706	+ validReopen(t, 1, 100)
	707	+
	708	+ if err := l.TruncateFront(2); err != nil {
	709	+ t.Fatal(err)
	710	+ }
	711	+ validReopen(t, 2, 100)
	712	+
	713	+ if err := l.TruncateFront(4); err != nil {
	714	+ t.Fatal(err)
	715	+ }
	716	+ validReopen(t, 4, 100)
	717	+
	718	+ if err := l.TruncateFront(5); err != nil {
	719	+ t.Fatal(err)
	720	+ }
	721	+ validReopen(t, 5, 100)
	722	+
	723	+ if err := l.TruncateFront(99); err != nil {
	724	+ t.Fatal(err)
	725	+ }
	726	+ validReopen(t, 99, 100)
	727	+
	728	+ if err := l.TruncateFront(100); err != nil {
	729	+ t.Fatal(err)
	730	+ }
	731	+ validReopen(t, 100, 100)
	732	+
	733	+}
	734	+
	735	+func TestSimpleTruncateBack(t *testing.T) {
	736	+ os.RemoveAll("testlog")
	737	+
	738	+ opts := &Options{
	739	+ NoSync: true,
	740	+ LogFormat: JSON,
	741	+ SegmentSize: 100,
	742	+ }
	743	+
	744	+ l, err := Open("testlog", opts)
	745	+ if err != nil {
	746	+ t.Fatal(err)
	747	+ }
	748	+ defer func() {
	749	+ l.Close()
	750	+ }()
	751	+
	752	+ makeData := func(index uint64) []byte {
	753	+ return []byte(fmt.Sprintf("data-%d", index))
	754	+ }
	755	+
	756	+ valid := func(t *testing.T, first, last uint64) {
	757	+ t.Helper()
	758	+ index, err := l.FirstIndex()
	759	+ if err != nil {
	760	+ t.Fatal(err)
	761	+ }
	762	+ if index != first {
	763	+ t.Fatalf("expected %v, got %v", first, index)
	764	+ }
	765	+ index, err = l.LastIndex()
	766	+ if err != nil {
	767	+ t.Fatal(err)
	768	+ }
	769	+ if index != last {
	770	+ t.Fatalf("expected %v, got %v", last, index)
	771	+ }
	772	+ for i := first; i <= last; i++ {
	773	+ data, err := l.Read(i)
	774	+ if err != nil {
	775	+ t.Fatal(err)
	776	+ }
	777	+ if string(data) != string(makeData(i)) {
	778	+ t.Fatalf("expcted '%s', got '%s'", makeData(i), data)
	779	+ }
	780	+ }
	781	+ }
	782	+ validReopen := func(t *testing.T, first, last uint64) {
	783	+ t.Helper()
	784	+ valid(t, first, last)
	785	+ if err := l.Close(); err != nil {
	786	+ t.Fatal(err)
	787	+ }
	788	+ l, err = Open("testlog", opts)
	789	+ if err != nil {
	790	+ t.Fatal(err)
	791	+ }
	792	+ valid(t, first, last)
	793	+ }
	794	+ for i := 1; i <= 100; i++ {
	795	+ err := l.Write(uint64(i), makeData(uint64(i)))
	796	+ if err != nil {
	797	+ t.Fatal(err)
	798	+ }
	799	+ }
	800	+ validReopen(t, 1, 100)
	801	+
	802	+ /////////////////////////////////////////////////////////////
	803	+ if err := l.TruncateBack(100); err != nil {
	804	+ t.Fatal(err)
	805	+ }
	806	+ validReopen(t, 1, 100)
	807	+ if err := l.Write(101, makeData(101)); err != nil {
	808	+ t.Fatal(err)
	809	+ }
	810	+ validReopen(t, 1, 101)
	811	+
	812	+ /////////////////////////////////////////////////////////////
	813	+ if err := l.TruncateBack(99); err != nil {
	814	+ t.Fatal(err)
	815	+ }
	816	+ validReopen(t, 1, 99)
	817	+ if err := l.Write(100, makeData(100)); err != nil {
	818	+ t.Fatal(err)
	819	+ }
	820	+ validReopen(t, 1, 100)
	821	+
	822	+ if err := l.TruncateBack(94); err != nil {
	823	+ t.Fatal(err)
	824	+ }
	825	+ validReopen(t, 1, 94)
	826	+
	827	+ if err := l.TruncateBack(93); err != nil {
	828	+ t.Fatal(err)
	829	+ }
	830	+ validReopen(t, 1, 93)
	831	+
	832	+ if err := l.TruncateBack(92); err != nil {
	833	+ t.Fatal(err)
	834	+ }
	835	+ validReopen(t, 1, 92)
	836	+
	837	+}

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