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Signed-off-by: Fabian Reinartz <freinartz@google.com>
This commit is contained in:
Fabian Reinartz 2018-06-18 07:52:57 -04:00
parent 0ad2b8a349
commit 3e76f0163e
4 changed files with 37 additions and 35 deletions
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16
checkpoint.go
View file

@ -35,9 +35,9 @@ type CheckpointStats struct {
DroppedSeries int
DroppedSamples int
DroppedTombstones int
TotalSeries int
TotalSamples int
TotalTombstones int
TotalSeries int // Processed series including dropped ones.
TotalSamples int // Processed samples inlcuding dropped ones.
TotalTombstones int // Processed tombstones including droppes ones.
}
// LastCheckpoint returns the directory name of the most recent checkpoint.
@ -129,16 +129,16 @@ func Checkpoint(logger log.Logger, w *wal.WAL, m, n int, keep func(id uint64) bo
sr = last
}
segs, err := wal.NewSegmentsRangeReader(w.Dir(), m, n)
segsr, err := wal.NewSegmentsRangeReader(w.Dir(), m, n)
if err != nil {
return nil, errors.Wrap(err, "create segment reader")
}
defer segs.Close()
defer segsr.Close()
if sr != nil {
sr = io.MultiReader(sr, segs)
sr = io.MultiReader(sr, segsr)
} else {
sr = segs
sr = segsr
}
}
@ -169,7 +169,7 @@ func Checkpoint(logger log.Logger, w *wal.WAL, m, n int, keep func(id uint64) bo
// We don't reset the buffer since we batch up multiple records
// before writing them to the checkpoint.
// Remember where the record for this iteration starts.
// Remember where the record for this iteration starts.
start := len(buf)
rec := r.Record()

16
docs/format/wal.md
View file

@ -5,14 +5,17 @@ e.g. `000000`, `000001`, `000002`, etc., and are limited to 128MB by default.
A segment is written to in pages of 32KB. Only the last page of the most recent segment
may be partial. A WAL record is an opaque byte slice that gets split up into sub-records
should it exceed the remaining space of the current page. Records are never split across
segment boundaries.
The encoding of pages is largely borrowed from [LevelDB's/RocksDB's wirte ahead log.][1]
segment boundaries. If a single record exceeds the default segment size, a segment with
a larger size will be created.
The encoding of pages is largely borrowed from [LevelDB's/RocksDB's write ahead log.][1]
Notable deviations are that the record fragment is encoded as:
```
┌───────────┬──────────┬────────────┬──────────────┐
│ type <1b> │ len <2b> │ CRC32 <4b> │ data <bytes> │
└───────────┴──────────┴────────────┴──────────────┘
```
## Record encoding
@ -22,6 +25,7 @@ The records written to the write ahead log are encoded as follows:
Series records encode the labels that identifier a series and its unique ID.
```
┌────────────────────────────────────────────┐
│ type = 1 <1b> │
├────────────────────────────────────────────┤
@ -36,12 +40,14 @@ Series records encode the labels that identifier a series and its unique ID.
│ └───────────────────────┴────────────────┘ │
│ . . . │
└────────────────────────────────────────────┘
```
### Sample records
Sample records encode samples as a list of triples `(series_id, timestamp, value)`.
Series reference and timestamp are encoded as deltas w.r.t the first sample.
```
┌──────────────────────────────────────────────────────────────────┐
│ type = 2 <1b> │
├──────────────────────────────────────────────────────────────────┤
@ -53,13 +59,14 @@ Series reference and timestamp are encoded as deltas w.r.t the first sample.
│ └────────────────────┴───────────────────────────┴─────────────┘ │
│ . . . │
└──────────────────────────────────────────────────────────────────┘
```
### Tombstone records
Tombstone records encode tombstones as a list of triples `(series_id, min_time, max_time)`
and specify an interval for which samples of a series got deleted.
```
┌─────────────────────────────────────────────────────┐
│ type = 3 <1b> │
├─────────────────────────────────────────────────────┤
@ -68,5 +75,6 @@ and specify an interval for which samples of a series got deleted.
│ └─────────┴───────────────────┴───────────────────┘ │
│ . . . │
└─────────────────────────────────────────────────────┘
```
[1][https://github.com/facebook/rocksdb/wiki/Write-Ahead-Log-File-Format]
[1][https://github.com/facebook/rocksdb/wiki/Write-Ahead-Log-File-Format]

2
head.go
View file

@ -438,7 +438,7 @@ func (h *Head) Truncate(mint int64) error {
return nil // no segments yet.
}
// The lower third of segments should contain mostly obsolete samples.
// If we have too few segments, it's not worth checkpointing yet.
// If we have less than three segments, it's not worth checkpointing yet.
n = m + (n-m)/3
if n <= m {
return nil

38
wal/wal.go
View file

@ -23,6 +23,7 @@ import (
"math"
"os"
"path/filepath"
"sort"
"strconv"
"sync"
"time"
@ -35,9 +36,7 @@ import (
)
const (
version = 1
defaultSegmentSize = 128 * 1024 * 1024 // 128 MB
maxRecordSize = 1 * 1024 * 1024 // 1MB
pageSize = 32 * 1024 // 32KB
recordHeaderSize = 7
)
@ -94,7 +93,6 @@ func (e *CorruptionErr) Error() string {
// OpenWriteSegment opens segment k in dir. The returned segment is ready for new appends.
func OpenWriteSegment(dir string, k int) (*Segment, error) {
// Only .active segments are allowed to be opened for write.
f, err := os.OpenFile(SegmentName(dir, k), os.O_WRONLY|os.O_APPEND, 0666)
if err != nil {
return nil, err
@ -127,7 +125,7 @@ func CreateSegment(dir string, k int) (*Segment, error) {
return &Segment{File: f, i: k, dir: dir}, nil
}
// OpenReadSegment opens the segment k in dir for reading.
// OpenReadSegment opens the segment with the given filename.
func OpenReadSegment(fn string) (*Segment, error) {
k, err := strconv.Atoi(filepath.Base(fn))
if err != nil {
@ -142,7 +140,7 @@ func OpenReadSegment(fn string) (*Segment, error) {
// 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 errore occurs during read, the repair procedure must be called
// If an erroe 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
@ -244,23 +242,19 @@ Loop:
case f := <-w.actorc:
f()
case donec := <-w.stopc:
close(w.actorc)
defer close(donec)
break Loop
}
}
// Drain and process any remaining functions.
for {
select {
case f := <-w.actorc:
f()
default:
return
}
for f := range w.actorc {
f()
}
}
// Repair attempts to repair the WAL based on the error.
// It discards all data behind the corruption
// It discards all data after the corruption.
func (w *WAL) Repair(err error) error {
// We could probably have a mode that only discards torn records right around
// the corruption to preserve as data much as possible.
@ -333,7 +327,7 @@ func (w *WAL) Repair(err error) error {
// SegmentName builds a segment name for the directory.
func SegmentName(dir string, i int) string {
return filepath.Join(dir, fmt.Sprintf("%06d", i))
return filepath.Join(dir, fmt.Sprintf("%08d", i))
}
// nextSegment creates the next segment and closes the previous one.
@ -384,6 +378,7 @@ func (w *WAL) flushPage(clear bool) error {
}
p.flushed += n
// We flushed an entire page, prepare a new one.
if clear {
for i := range p.buf {
p.buf[i] = 0
@ -485,7 +480,7 @@ func (w *WAL) log(rec []byte, final bool) error {
binary.BigEndian.PutUint16(buf[1:], uint16(len(part)))
binary.BigEndian.PutUint32(buf[3:], crc)
copy(buf[7:], part)
copy(buf[recordHeaderSize:], part)
p.alloc += len(part) + recordHeaderSize
// If we wrote a full record, we can fit more records of the batch
@ -587,6 +582,9 @@ func listSegments(dir string) (refs []segmentRef, err error) {
refs = append(refs, segmentRef{s: fn, n: k})
last = k
}
sort.Slice(refs, func(i, j int) bool {
return refs[i].n < refs[j].n
})
return refs, nil
}
@ -667,10 +665,6 @@ func (r *segmentBufReader) Read(b []byte) (n int, err error) {
// Only unset more so we don't invalidate the current segment and
// offset before the next read.
r.more = false
// If no more segments are left, it's the end for the reader.
if len(r.segs) == 0 {
return n, io.EOF
}
return n, nil
}
@ -689,7 +683,7 @@ func NewReader(r io.Reader) *Reader {
}
// Next advances the reader to the next records and returns true if it exists.
// It must not be called once after it returned false.
// It must not be called again after it returned false.
func (r *Reader) Next() bool {
err := r.next()
if errors.Cause(err) == io.EOF {
@ -702,8 +696,8 @@ func (r *Reader) Next() bool {
func (r *Reader) next() (err error) {
// We have to use r.buf since allocating byte arrays here fails escape
// analysis and ends up on the heap, even though it seemingly should not.
hdr := r.buf[:7]
buf := r.buf[7:]
hdr := r.buf[:recordHeaderSize]
buf := r.buf[recordHeaderSize:]
r.rec = r.rec[:0]