prometheus/tsdb/wal/wal.go

987 lines
26 KiB
Go

// Copyright 2017 The Prometheus 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 wal
import (
"bufio"
"encoding/binary"
"fmt"
"hash/crc32"
"io"
"os"
"path/filepath"
"sort"
"strconv"
"sync"
"time"
"github.com/go-kit/log"
"github.com/go-kit/log/level"
"github.com/golang/snappy"
"github.com/pkg/errors"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/prometheus/tsdb/fileutil"
)
const (
DefaultSegmentSize = 128 * 1024 * 1024 // 128 MB
pageSize = 32 * 1024 // 32KB
recordHeaderSize = 7
WblDirName = "wbl"
)
// The table gets initialized with sync.Once but may still cause a race
// with any other use of the crc32 package anywhere. Thus we initialize it
// before.
var castagnoliTable = crc32.MakeTable(crc32.Castagnoli)
// page is an in memory buffer used to batch disk writes.
// Records bigger than the page size are split and flushed separately.
// A flush is triggered when a single records doesn't fit the page size or
// when the next record can't fit in the remaining free page space.
type page struct {
alloc int
flushed int
buf [pageSize]byte
}
func (p *page) remaining() int {
return pageSize - p.alloc
}
func (p *page) full() bool {
return pageSize-p.alloc < recordHeaderSize
}
func (p *page) reset() {
for i := range p.buf {
p.buf[i] = 0
}
p.alloc = 0
p.flushed = 0
}
// SegmentFile represents the underlying file used to store a segment.
type SegmentFile interface {
Stat() (os.FileInfo, error)
Sync() error
io.Writer
io.Reader
io.Closer
}
// Segment represents a segment file.
type Segment struct {
SegmentFile
dir string
i int
}
// Index returns the index of the segment.
func (s *Segment) Index() int {
return s.i
}
// Dir returns the directory of the segment.
func (s *Segment) Dir() string {
return s.dir
}
// CorruptionErr is an error that's returned when corruption is encountered.
type CorruptionErr struct {
Dir string
Segment int
Offset int64
Err error
}
func (e *CorruptionErr) Error() string {
if e.Segment < 0 {
return fmt.Sprintf("corruption after %d bytes: %s", e.Offset, e.Err)
}
return fmt.Sprintf("corruption in segment %s at %d: %s", SegmentName(e.Dir, e.Segment), e.Offset, e.Err)
}
// OpenWriteSegment opens segment k in dir. The returned segment is ready for new appends.
func OpenWriteSegment(logger log.Logger, dir string, k int) (*Segment, error) {
segName := SegmentName(dir, k)
f, err := os.OpenFile(segName, os.O_WRONLY|os.O_APPEND, 0o666)
if err != nil {
return nil, err
}
stat, err := f.Stat()
if err != nil {
f.Close()
return nil, err
}
// If the last page is torn, fill it with zeros.
// In case it was torn after all records were written successfully, this
// will just pad the page and everything will be fine.
// If it was torn mid-record, a full read (which the caller should do anyway
// to ensure integrity) will detect it as a corruption by the end.
if d := stat.Size() % pageSize; d != 0 {
level.Warn(logger).Log("msg", "Last page of the wal is torn, filling it with zeros", "segment", segName)
if _, err := f.Write(make([]byte, pageSize-d)); err != nil {
f.Close()
return nil, errors.Wrap(err, "zero-pad torn page")
}
}
return &Segment{SegmentFile: f, i: k, dir: dir}, nil
}
// CreateSegment creates a new segment k in dir.
func CreateSegment(dir string, k int) (*Segment, error) {
f, err := os.OpenFile(SegmentName(dir, k), os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0o666)
if err != nil {
return nil, err
}
return &Segment{SegmentFile: f, i: k, dir: dir}, nil
}
// OpenReadSegment opens the segment with the given filename.
func OpenReadSegment(fn string) (*Segment, error) {
k, err := strconv.Atoi(filepath.Base(fn))
if err != nil {
return nil, errors.New("not a valid filename")
}
f, err := os.Open(fn)
if err != nil {
return nil, err
}
return &Segment{SegmentFile: f, i: k, dir: filepath.Dir(fn)}, nil
}
// WAL is a write ahead log that stores records in segment files.
// It must be read from start to end once before logging new data.
// If an error occurs during read, the repair procedure must be called
// before it's safe to do further writes.
//
// Segments are written to in pages of 32KB, with records possibly split
// across page boundaries.
// Records are never split across segments to allow full segments to be
// safely truncated. It also ensures that torn writes never corrupt records
// beyond the most recent segment.
type WAL struct {
dir string
logger log.Logger
segmentSize int
mtx sync.RWMutex
segment *Segment // Active segment.
donePages int // Pages written to the segment.
page *page // Active page.
stopc chan chan struct{}
actorc chan func()
closed bool // To allow calling Close() more than once without blocking.
compress bool
snappyBuf []byte
metrics *walMetrics
}
type walMetrics struct {
fsyncDuration prometheus.Summary
pageFlushes prometheus.Counter
pageCompletions prometheus.Counter
truncateFail prometheus.Counter
truncateTotal prometheus.Counter
currentSegment prometheus.Gauge
writesFailed prometheus.Counter
}
func newWALMetrics(r prometheus.Registerer) *walMetrics {
m := &walMetrics{}
m.fsyncDuration = prometheus.NewSummary(prometheus.SummaryOpts{
Name: "fsync_duration_seconds",
Help: "Duration of WAL fsync.",
Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
})
m.pageFlushes = prometheus.NewCounter(prometheus.CounterOpts{
Name: "page_flushes_total",
Help: "Total number of page flushes.",
})
m.pageCompletions = prometheus.NewCounter(prometheus.CounterOpts{
Name: "completed_pages_total",
Help: "Total number of completed pages.",
})
m.truncateFail = prometheus.NewCounter(prometheus.CounterOpts{
Name: "truncations_failed_total",
Help: "Total number of WAL truncations that failed.",
})
m.truncateTotal = prometheus.NewCounter(prometheus.CounterOpts{
Name: "truncations_total",
Help: "Total number of WAL truncations attempted.",
})
m.currentSegment = prometheus.NewGauge(prometheus.GaugeOpts{
Name: "segment_current",
Help: "WAL segment index that TSDB is currently writing to.",
})
m.writesFailed = prometheus.NewCounter(prometheus.CounterOpts{
Name: "writes_failed_total",
Help: "Total number of WAL writes that failed.",
})
if r != nil {
r.MustRegister(
m.fsyncDuration,
m.pageFlushes,
m.pageCompletions,
m.truncateFail,
m.truncateTotal,
m.currentSegment,
m.writesFailed,
)
}
return m
}
// New returns a new WAL over the given directory.
func New(logger log.Logger, reg prometheus.Registerer, dir string, compress bool) (*WAL, error) {
return NewSize(logger, reg, dir, DefaultSegmentSize, compress)
}
// NewSize returns a new WAL over the given directory.
// New segments are created with the specified size.
func NewSize(logger log.Logger, reg prometheus.Registerer, dir string, segmentSize int, compress bool) (*WAL, error) {
if segmentSize%pageSize != 0 {
return nil, errors.New("invalid segment size")
}
if err := os.MkdirAll(dir, 0o777); err != nil {
return nil, errors.Wrap(err, "create dir")
}
if logger == nil {
logger = log.NewNopLogger()
}
w := &WAL{
dir: dir,
logger: logger,
segmentSize: segmentSize,
page: &page{},
actorc: make(chan func(), 100),
stopc: make(chan chan struct{}),
compress: compress,
}
prefix := "prometheus_tsdb_wal_"
if filepath.Base(dir) == WblDirName {
prefix = "prometheus_tsdb_out_of_order_wal_"
}
w.metrics = newWALMetrics(prometheus.WrapRegistererWithPrefix(prefix, reg))
_, last, err := Segments(w.Dir())
if err != nil {
return nil, errors.Wrap(err, "get segment range")
}
// Index of the Segment we want to open and write to.
writeSegmentIndex := 0
// If some segments already exist create one with a higher index than the last segment.
if last != -1 {
writeSegmentIndex = last + 1
}
segment, err := CreateSegment(w.Dir(), writeSegmentIndex)
if err != nil {
return nil, err
}
if err := w.setSegment(segment); err != nil {
return nil, err
}
go w.run()
return w, nil
}
// Open an existing WAL.
func Open(logger log.Logger, dir string) (*WAL, error) {
if logger == nil {
logger = log.NewNopLogger()
}
w := &WAL{
dir: dir,
logger: logger,
}
return w, nil
}
// CompressionEnabled returns if compression is enabled on this WAL.
func (w *WAL) CompressionEnabled() bool {
return w.compress
}
// Dir returns the directory of the WAL.
func (w *WAL) Dir() string {
return w.dir
}
func (w *WAL) run() {
Loop:
for {
select {
case f := <-w.actorc:
f()
case donec := <-w.stopc:
close(w.actorc)
defer close(donec)
break Loop
}
}
// Drain and process any remaining functions.
for f := range w.actorc {
f()
}
}
// Repair attempts to repair the WAL based on the error.
// It discards all data after the corruption.
func (w *WAL) Repair(origErr error) error {
// We could probably have a mode that only discards torn records right around
// the corruption to preserve as data much as possible.
// But that's not generally applicable if the records have any kind of causality.
// Maybe as an extra mode in the future if mid-WAL corruptions become
// a frequent concern.
err := errors.Cause(origErr) // So that we can pick up errors even if wrapped.
cerr, ok := err.(*CorruptionErr)
if !ok {
return errors.Wrap(origErr, "cannot handle error")
}
if cerr.Segment < 0 {
return errors.New("corruption error does not specify position")
}
level.Warn(w.logger).Log("msg", "Starting corruption repair",
"segment", cerr.Segment, "offset", cerr.Offset)
// All segments behind the corruption can no longer be used.
segs, err := listSegments(w.Dir())
if err != nil {
return errors.Wrap(err, "list segments")
}
level.Warn(w.logger).Log("msg", "Deleting all segments newer than corrupted segment", "segment", cerr.Segment)
for _, s := range segs {
if w.segment.i == s.index {
// The active segment needs to be removed,
// close it first (Windows!). Can be closed safely
// as we set the current segment to repaired file
// below.
if err := w.segment.Close(); err != nil {
return errors.Wrap(err, "close active segment")
}
}
if s.index <= cerr.Segment {
continue
}
if err := os.Remove(filepath.Join(w.Dir(), s.name)); err != nil {
return errors.Wrapf(err, "delete segment:%v", s.index)
}
}
// Regardless of the corruption offset, no record reaches into the previous segment.
// So we can safely repair the WAL by removing the segment and re-inserting all
// its records up to the corruption.
level.Warn(w.logger).Log("msg", "Rewrite corrupted segment", "segment", cerr.Segment)
fn := SegmentName(w.Dir(), cerr.Segment)
tmpfn := fn + ".repair"
if err := fileutil.Rename(fn, tmpfn); err != nil {
return err
}
// Create a clean segment and make it the active one.
s, err := CreateSegment(w.Dir(), cerr.Segment)
if err != nil {
return err
}
if err := w.setSegment(s); err != nil {
return err
}
f, err := os.Open(tmpfn)
if err != nil {
return errors.Wrap(err, "open segment")
}
defer f.Close()
r := NewReader(bufio.NewReader(f))
for r.Next() {
// Add records only up to the where the error was.
if r.Offset() >= cerr.Offset {
break
}
if err := w.Log(r.Record()); err != nil {
return errors.Wrap(err, "insert record")
}
}
// We expect an error here from r.Err(), so nothing to handle.
// We need to pad to the end of the last page in the repaired segment
if err := w.flushPage(true); err != nil {
return errors.Wrap(err, "flush page in repair")
}
// We explicitly close even when there is a defer for Windows to be
// able to delete it. The defer is in place to close it in-case there
// are errors above.
if err := f.Close(); err != nil {
return errors.Wrap(err, "close corrupted file")
}
if err := os.Remove(tmpfn); err != nil {
return errors.Wrap(err, "delete corrupted segment")
}
// Explicitly close the segment we just repaired to avoid issues with Windows.
s.Close()
// We always want to start writing to a new Segment rather than an existing
// Segment, which is handled by NewSize, but earlier in Repair we're deleting
// all segments that come after the corrupted Segment. Recreate a new Segment here.
s, err = CreateSegment(w.Dir(), cerr.Segment+1)
if err != nil {
return err
}
return w.setSegment(s)
}
// SegmentName builds a segment name for the directory.
func SegmentName(dir string, i int) string {
return filepath.Join(dir, fmt.Sprintf("%08d", i))
}
// NextSegment creates the next segment and closes the previous one asynchronously.
// It returns the file number of the new file.
func (w *WAL) NextSegment() (int, error) {
w.mtx.Lock()
defer w.mtx.Unlock()
return w.nextSegment(true)
}
// NextSegmentSync creates the next segment and closes the previous one in sync.
// It returns the file number of the new file.
func (w *WAL) NextSegmentSync() (int, error) {
w.mtx.Lock()
defer w.mtx.Unlock()
return w.nextSegment(false)
}
// nextSegment creates the next segment and closes the previous one.
// It returns the file number of the new file.
func (w *WAL) nextSegment(async bool) (int, error) {
if w.closed {
return 0, errors.New("wal is closed")
}
// Only flush the current page if it actually holds data.
if w.page.alloc > 0 {
if err := w.flushPage(true); err != nil {
return 0, err
}
}
next, err := CreateSegment(w.Dir(), w.segment.Index()+1)
if err != nil {
return 0, errors.Wrap(err, "create new segment file")
}
prev := w.segment
if err := w.setSegment(next); err != nil {
return 0, err
}
// Don't block further writes by fsyncing the last segment.
f := func() {
if err := w.fsync(prev); err != nil {
level.Error(w.logger).Log("msg", "sync previous segment", "err", err)
}
if err := prev.Close(); err != nil {
level.Error(w.logger).Log("msg", "close previous segment", "err", err)
}
}
if async {
w.actorc <- f
} else {
f()
}
return next.Index(), nil
}
func (w *WAL) setSegment(segment *Segment) error {
w.segment = segment
// Correctly initialize donePages.
stat, err := segment.Stat()
if err != nil {
return err
}
w.donePages = int(stat.Size() / pageSize)
w.metrics.currentSegment.Set(float64(segment.Index()))
return nil
}
// flushPage writes the new contents of the page to disk. If no more records will fit into
// the page, the remaining bytes will be set to zero and a new page will be started.
// If clear is true, this is enforced regardless of how many bytes are left in the page.
func (w *WAL) flushPage(clear bool) error {
w.metrics.pageFlushes.Inc()
p := w.page
clear = clear || p.full()
// No more data will fit into the page or an implicit clear.
// Enqueue and clear it.
if clear {
p.alloc = pageSize // Write till end of page.
}
n, err := w.segment.Write(p.buf[p.flushed:p.alloc])
if err != nil {
p.flushed += n
return err
}
p.flushed += n
// We flushed an entire page, prepare a new one.
if clear {
p.reset()
w.donePages++
w.metrics.pageCompletions.Inc()
}
return nil
}
// First Byte of header format:
// [ 4 bits unallocated] [1 bit snappy compression flag] [ 3 bit record type ]
const (
snappyMask = 1 << 3
recTypeMask = snappyMask - 1
)
type recType uint8
const (
recPageTerm recType = 0 // Rest of page is empty.
recFull recType = 1 // Full record.
recFirst recType = 2 // First fragment of a record.
recMiddle recType = 3 // Middle fragments of a record.
recLast recType = 4 // Final fragment of a record.
)
func recTypeFromHeader(header byte) recType {
return recType(header & recTypeMask)
}
func (t recType) String() string {
switch t {
case recPageTerm:
return "zero"
case recFull:
return "full"
case recFirst:
return "first"
case recMiddle:
return "middle"
case recLast:
return "last"
default:
return "<invalid>"
}
}
func (w *WAL) pagesPerSegment() int {
return w.segmentSize / pageSize
}
// Log writes the records into the log.
// Multiple records can be passed at once to reduce writes and increase throughput.
func (w *WAL) Log(recs ...[]byte) error {
w.mtx.Lock()
defer w.mtx.Unlock()
// Callers could just implement their own list record format but adding
// a bit of extra logic here frees them from that overhead.
for i, r := range recs {
if err := w.log(r, i == len(recs)-1); err != nil {
w.metrics.writesFailed.Inc()
return err
}
}
return nil
}
// log writes rec to the log and forces a flush of the current page if:
// - the final record of a batch
// - the record is bigger than the page size
// - the current page is full.
func (w *WAL) log(rec []byte, final bool) error {
// When the last page flush failed the page will remain full.
// When the page is full, need to flush it before trying to add more records to it.
if w.page.full() {
if err := w.flushPage(true); err != nil {
return err
}
}
// Compress the record before calculating if a new segment is needed.
compressed := false
if w.compress &&
len(rec) > 0 &&
// If MaxEncodedLen is less than 0 the record is too large to be compressed.
snappy.MaxEncodedLen(len(rec)) >= 0 {
// The snappy library uses `len` to calculate if we need a new buffer.
// In order to allocate as few buffers as possible make the length
// equal to the capacity.
w.snappyBuf = w.snappyBuf[:cap(w.snappyBuf)]
w.snappyBuf = snappy.Encode(w.snappyBuf, rec)
if len(w.snappyBuf) < len(rec) {
rec = w.snappyBuf
compressed = true
}
}
// If the record is too big to fit within the active page in the current
// segment, terminate the active segment and advance to the next one.
// This ensures that records do not cross segment boundaries.
left := w.page.remaining() - recordHeaderSize // Free space in the active page.
left += (pageSize - recordHeaderSize) * (w.pagesPerSegment() - w.donePages - 1) // Free pages in the active segment.
if len(rec) > left {
if _, err := w.nextSegment(true); err != nil {
return err
}
}
// Populate as many pages as necessary to fit the record.
// Be careful to always do one pass to ensure we write zero-length records.
for i := 0; i == 0 || len(rec) > 0; i++ {
p := w.page
// Find how much of the record we can fit into the page.
var (
l = min(len(rec), (pageSize-p.alloc)-recordHeaderSize)
part = rec[:l]
buf = p.buf[p.alloc:]
typ recType
)
switch {
case i == 0 && len(part) == len(rec):
typ = recFull
case len(part) == len(rec):
typ = recLast
case i == 0:
typ = recFirst
default:
typ = recMiddle
}
if compressed {
typ |= snappyMask
}
buf[0] = byte(typ)
crc := crc32.Checksum(part, castagnoliTable)
binary.BigEndian.PutUint16(buf[1:], uint16(len(part)))
binary.BigEndian.PutUint32(buf[3:], crc)
copy(buf[recordHeaderSize:], part)
p.alloc += len(part) + recordHeaderSize
if w.page.full() {
if err := w.flushPage(true); err != nil {
// TODO When the flushing fails at this point and the record has not been
// fully written to the buffer, we end up with a corrupted WAL because some part of the
// record have been written to the buffer, while the rest of the record will be discarded.
return err
}
}
rec = rec[l:]
}
// If it's the final record of the batch and the page is not empty, flush it.
if final && w.page.alloc > 0 {
if err := w.flushPage(false); err != nil {
return err
}
}
return nil
}
// LastSegmentAndOffset returns the last segment number of the WAL
// and the offset in that file upto which the segment has been filled.
func (w *WAL) LastSegmentAndOffset() (seg, offset int, err error) {
w.mtx.Lock()
defer w.mtx.Unlock()
_, seg, err = Segments(w.Dir())
if err != nil {
return
}
offset = (w.donePages * pageSize) + w.page.alloc
return
}
// Truncate drops all segments before i.
func (w *WAL) Truncate(i int) (err error) {
w.metrics.truncateTotal.Inc()
defer func() {
if err != nil {
w.metrics.truncateFail.Inc()
}
}()
refs, err := listSegments(w.Dir())
if err != nil {
return err
}
for _, r := range refs {
if r.index >= i {
break
}
if err = os.Remove(filepath.Join(w.Dir(), r.name)); err != nil {
return err
}
}
return nil
}
func (w *WAL) fsync(f *Segment) error {
start := time.Now()
err := f.Sync()
w.metrics.fsyncDuration.Observe(time.Since(start).Seconds())
return err
}
// Sync forces a file sync on the current wal segment. This function is meant
// to be used only on tests due to different behaviour on Operating Systems
// like windows and linux
func (w *WAL) Sync() error {
return w.fsync(w.segment)
}
// Close flushes all writes and closes active segment.
func (w *WAL) Close() (err error) {
w.mtx.Lock()
defer w.mtx.Unlock()
if w.closed {
return errors.New("wal already closed")
}
if w.segment == nil {
w.closed = true
return nil
}
// Flush the last page and zero out all its remaining size.
// We must not flush an empty page as it would falsely signal
// the segment is done if we start writing to it again after opening.
if w.page.alloc > 0 {
if err := w.flushPage(true); err != nil {
return err
}
}
donec := make(chan struct{})
w.stopc <- donec
<-donec
if err = w.fsync(w.segment); err != nil {
level.Error(w.logger).Log("msg", "sync previous segment", "err", err)
}
if err := w.segment.Close(); err != nil {
level.Error(w.logger).Log("msg", "close previous segment", "err", err)
}
w.closed = true
return nil
}
// Segments returns the range [first, n] of currently existing segments.
// If no segments are found, first and n are -1.
func Segments(walDir string) (first, last int, err error) {
refs, err := listSegments(walDir)
if err != nil {
return 0, 0, err
}
if len(refs) == 0 {
return -1, -1, nil
}
return refs[0].index, refs[len(refs)-1].index, nil
}
type segmentRef struct {
name string
index int
}
func listSegments(dir string) (refs []segmentRef, err error) {
files, err := os.ReadDir(dir)
if err != nil {
return nil, err
}
for _, f := range files {
fn := f.Name()
k, err := strconv.Atoi(fn)
if err != nil {
continue
}
refs = append(refs, segmentRef{name: fn, index: k})
}
sort.Slice(refs, func(i, j int) bool {
return refs[i].index < refs[j].index
})
for i := 0; i < len(refs)-1; i++ {
if refs[i].index+1 != refs[i+1].index {
return nil, errors.New("segments are not sequential")
}
}
return refs, nil
}
// SegmentRange groups segments by the directory and the first and last index it includes.
type SegmentRange struct {
Dir string
First, Last int
}
// NewSegmentsReader returns a new reader over all segments in the directory.
func NewSegmentsReader(dir string) (io.ReadCloser, error) {
return NewSegmentsRangeReader(SegmentRange{dir, -1, -1})
}
// NewSegmentsRangeReader returns a new reader over the given WAL segment ranges.
// If first or last are -1, the range is open on the respective end.
func NewSegmentsRangeReader(sr ...SegmentRange) (io.ReadCloser, error) {
var segs []*Segment
for _, sgmRange := range sr {
refs, err := listSegments(sgmRange.Dir)
if err != nil {
return nil, errors.Wrapf(err, "list segment in dir:%v", sgmRange.Dir)
}
for _, r := range refs {
if sgmRange.First >= 0 && r.index < sgmRange.First {
continue
}
if sgmRange.Last >= 0 && r.index > sgmRange.Last {
break
}
s, err := OpenReadSegment(filepath.Join(sgmRange.Dir, r.name))
if err != nil {
return nil, errors.Wrapf(err, "open segment:%v in dir:%v", r.name, sgmRange.Dir)
}
segs = append(segs, s)
}
}
return NewSegmentBufReader(segs...), nil
}
// segmentBufReader is a buffered reader that reads in multiples of pages.
// The main purpose is that we are able to track segment and offset for
// corruption reporting. We have to be careful not to increment curr too
// early, as it is used by Reader.Err() to tell Repair which segment is corrupt.
// As such we pad the end of non-page align segments with zeros.
type segmentBufReader struct {
buf *bufio.Reader
segs []*Segment
cur int // Index into segs.
off int // Offset of read data into current segment.
}
// nolint:revive // TODO: Consider exporting segmentBufReader
func NewSegmentBufReader(segs ...*Segment) *segmentBufReader {
if len(segs) == 0 {
return &segmentBufReader{}
}
return &segmentBufReader{
buf: bufio.NewReaderSize(segs[0], 16*pageSize),
segs: segs,
}
}
// nolint:revive
func NewSegmentBufReaderWithOffset(offset int, segs ...*Segment) (sbr *segmentBufReader, err error) {
if offset == 0 || len(segs) == 0 {
return NewSegmentBufReader(segs...), nil
}
sbr = &segmentBufReader{
buf: bufio.NewReaderSize(segs[0], 16*pageSize),
segs: segs,
}
if offset > 0 {
_, err = sbr.buf.Discard(offset)
}
return sbr, err
}
func (r *segmentBufReader) Close() (err error) {
for _, s := range r.segs {
if e := s.Close(); e != nil {
err = e
}
}
return err
}
// Read implements io.Reader.
func (r *segmentBufReader) Read(b []byte) (n int, err error) {
if len(r.segs) == 0 {
return 0, io.EOF
}
n, err = r.buf.Read(b)
r.off += n
// If we succeeded, or hit a non-EOF, we can stop.
if err == nil || err != io.EOF {
return n, err
}
// We hit EOF; fake out zero padding at the end of short segments, so we
// don't increment curr too early and report the wrong segment as corrupt.
if r.off%pageSize != 0 {
i := 0
for ; n+i < len(b) && (r.off+i)%pageSize != 0; i++ {
b[n+i] = 0
}
// Return early, even if we didn't fill b.
r.off += i
return n + i, nil
}
// There is no more deta left in the curr segment and there are no more
// segments left. Return EOF.
if r.cur+1 >= len(r.segs) {
return n, io.EOF
}
// Move to next segment.
r.cur++
r.off = 0
r.buf.Reset(r.segs[r.cur])
return n, nil
}
// Computing size of the WAL.
// We do this by adding the sizes of all the files under the WAL dir.
func (w *WAL) Size() (int64, error) {
return fileutil.DirSize(w.Dir())
}