Migrate write ahead log

On startup, rewrite the old write ahead log into the new format once.

Signed-off-by: Fabian Reinartz <freinartz@google.com>

db.go

@@ -192,6 +192,10 @@ func Open(dir string, l log.Logger, r prometheus.Registerer, opts *Options) (db
 	if err := repairBadIndexVersion(l, dir); err != nil {
 		return nil, err
 	}
+	// Migrate old WAL.
+	if err := MigrateWAL(l, filepath.Join(dir, "wal")); err != nil {
+		return nil, errors.Wrap(err, "migrate WAL")
+	}
 
 	db = &DB{
 		dir:                dir,

head.go

@@ -392,6 +392,8 @@ func (h *Head) Init() error {
 	if err == nil {
 		return nil
 	}
+	level.Warn(h.logger).Log("msg", "encountered WAL error, attempting repair", "err", err)
+
 	if err := h.wal.Repair(err); err != nil {
 		return errors.Wrap(err, "repair corrupted WAL")
 	}

wal.go

@@ -33,6 +33,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/tsdb/fileutil"
 	"github.com/prometheus/tsdb/labels"
+	"github.com/prometheus/tsdb/wal"
 )
 
 // WALEntryType indicates what data a WAL entry contains.
@@ -82,6 +83,8 @@ func newWalMetrics(wal *SegmentWAL, r prometheus.Registerer) *walMetrics {
 
 // WAL is a write ahead log that can log new series labels and samples.
 // It must be completely read before new entries are logged.
+//
+// DEPRECATED: use wal pkg combined with the record coders instead.
 type WAL interface {
 	Reader() WALReader
 	LogSeries([]RefSeries) error
@@ -173,6 +176,8 @@ func newCRC32() hash.Hash32 {
 }
 
 // SegmentWAL is a write ahead log for series data.
+//
+// DEPRECATED: use wal pkg combined with the record coders instead.
 type SegmentWAL struct {
 	mtx     sync.Mutex
 	metrics *walMetrics
@@ -1206,3 +1211,86 @@ func (r *walReader) decodeDeletes(flag byte, b []byte, res *[]Stone) error {
 	}
 	return nil
 }
+
+// MigrateWAL rewrites the deprecated write ahead log into the new format.
+func MigrateWAL(logger log.Logger, dir string) error {
+	// Detect whether we still have the old WAL.
+	fns, err := sequenceFiles(dir)
+	if err != nil && !os.IsNotExist(err) {
+		return errors.Wrap(err, "list sequence files")
+	}
+	if len(fns) == 0 {
+		return nil // No WAL at all yet.
+	}
+	// Check header of first segment.
+	f, err := os.Open(fns[0])
+	if err != nil {
+		return errors.Wrap(err, "check first existing segment")
+	}
+	var hdr [4]byte
+	if n, err := f.Read(hdr[:]); err != nil {
+		return errors.Wrap(err, "read header from first segment")
+	} else if n != 4 {
+		return errors.New("could not read full header from segment")
+	}
+	if binary.BigEndian.Uint32(hdr[:]) != WALMagic {
+		return nil // Not the old WAL anymore.
+	}
+
+	level.Info(logger).Log("msg", "migrating WAL format")
+
+	tmpdir := dir + ".tmp"
+	if err := os.RemoveAll(tmpdir); err != nil {
+		return errors.Wrap(err, "cleanup replacement dir")
+	}
+	repl, err := wal.New(logger, nil, tmpdir)
+	if err != nil {
+		return errors.Wrap(err, "open new WAL")
+	}
+	w, err := OpenSegmentWAL(dir, logger, time.Minute, nil)
+	if err != nil {
+		return errors.Wrap(err, "open old WAL")
+	}
+	rdr := w.Reader()
+
+	var (
+		enc RecordEncoder
+		b   []byte
+	)
+	decErr := rdr.Read(
+		func(s []RefSeries) {
+			if err != nil {
+				return
+			}
+			err = repl.Log(enc.Series(s, b[:0]))
+		},
+		func(s []RefSample) {
+			if err != nil {
+				return
+			}
+			err = repl.Log(enc.Samples(s, b[:0]))
+		},
+		func(s []Stone) {
+			if err != nil {
+				return
+			}
+			err = repl.Log(enc.Tombstones(s, b[:0]))
+		},
+	)
+	if decErr != nil {
+		return errors.Wrap(err, "decode old entries")
+	}
+	if err != nil {
+		return errors.Wrap(err, "write new entries")
+	}
+	if err := w.Close(); err != nil {
+		return errors.Wrap(err, "close old WAL")
+	}
+	if err := repl.Close(); err != nil {
+		return errors.Wrap(err, "close new WAL")
+	}
+	if err := fileutil.Rename(tmpdir, dir); err != nil {
+		return errors.Wrap(err, "replace old WAL")
+	}
+	return nil
+}

wal_test.go

@@ -19,6 +19,7 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"os"
+	"path"
 	"testing"
 	"time"
 
@@ -26,6 +27,7 @@ import (
 	"github.com/prometheus/tsdb/fileutil"
 	"github.com/prometheus/tsdb/labels"
 	"github.com/prometheus/tsdb/testutil"
+	"github.com/prometheus/tsdb/wal"
 )
 
 func TestSegmentWAL_cut(t *testing.T) {
@@ -431,3 +433,100 @@ func TestWALRestoreCorrupted(t *testing.T) {
 		})
 	}
 }
+
+func TestMigrateWAL_Fuzz(t *testing.T) {
+	dir, err := ioutil.TempDir("", "walmigrate")
+	testutil.Ok(t, err)
+	defer os.RemoveAll(dir)
+
+	wdir := path.Join(dir, "wal")
+
+	// Should pass if no WAL exists yet.
+	testutil.Ok(t, MigrateWAL(nil, wdir))
+
+	oldWAL, err := OpenSegmentWAL(wdir, nil, time.Minute, nil)
+	testutil.Ok(t, err)
+
+	// Write some data.
+	testutil.Ok(t, oldWAL.LogSeries([]RefSeries{
+		{Ref: 100, Labels: labels.FromStrings("abc", "def", "123", "456")},
+		{Ref: 1, Labels: labels.FromStrings("abc", "def2", "1234", "4567")},
+	}))
+	testutil.Ok(t, oldWAL.LogSamples([]RefSample{
+		{Ref: 1, T: 100, V: 200},
+		{Ref: 2, T: 300, V: 400},
+	}))
+	testutil.Ok(t, oldWAL.LogSeries([]RefSeries{
+		{Ref: 200, Labels: labels.FromStrings("xyz", "def", "foo", "bar")},
+	}))
+	testutil.Ok(t, oldWAL.LogSamples([]RefSample{
+		{Ref: 3, T: 100, V: 200},
+		{Ref: 4, T: 300, V: 400},
+	}))
+	testutil.Ok(t, oldWAL.LogDeletes([]Stone{
+		{ref: 1, intervals: []Interval{{100, 200}}},
+	}))
+
+	testutil.Ok(t, oldWAL.Close())
+
+	// Perform migration.
+	testutil.Ok(t, MigrateWAL(nil, wdir))
+
+	w, err := wal.New(nil, nil, wdir)
+	testutil.Ok(t, err)
+
+	// We can properly write some new data after migration.
+	var enc RecordEncoder
+	testutil.Ok(t, w.Log(enc.Samples([]RefSample{
+		{Ref: 500, T: 1, V: 1},
+	}, nil)))
+
+	testutil.Ok(t, w.Close())
+
+	// Read back all data.
+	sr, err := wal.NewSegmentsReader(wdir)
+	testutil.Ok(t, err)
+
+	r := wal.NewReader(sr)
+	var res []interface{}
+	var dec RecordDecoder
+
+	for r.Next() {
+		rec := r.Record()
+
+		switch dec.Type(rec) {
+		case RecordSeries:
+			s, err := dec.Series(rec, nil)
+			testutil.Ok(t, err)
+			res = append(res, s)
+		case RecordSamples:
+			s, err := dec.Samples(rec, nil)
+			testutil.Ok(t, err)
+			res = append(res, s)
+		case RecordTombstones:
+			s, err := dec.Tombstones(rec, nil)
+			testutil.Ok(t, err)
+			res = append(res, s)
+		default:
+			t.Fatalf("unknown record type %d", dec.Type(rec))
+		}
+	}
+	testutil.Ok(t, r.Err())
+
+	testutil.Equals(t, []interface{}{
+		[]RefSeries{
+			{Ref: 100, Labels: labels.FromStrings("abc", "def", "123", "456")},
+			{Ref: 1, Labels: labels.FromStrings("abc", "def2", "1234", "4567")},
+		},
+		[]RefSample{{Ref: 1, T: 100, V: 200}, {Ref: 2, T: 300, V: 400}},
+		[]RefSeries{
+			{Ref: 200, Labels: labels.FromStrings("xyz", "def", "foo", "bar")},
+		},
+		[]RefSample{{Ref: 3, T: 100, V: 200}, {Ref: 4, T: 300, V: 400}},
+		[]Stone{{ref: 1, intervals: []Interval{{100, 200}}}},
+		[]RefSample{{Ref: 500, T: 1, V: 1}},
+	}, res)
+
+	// Migrating an already migrated WAL shouldn't do anything.
+	testutil.Ok(t, MigrateWAL(nil, wdir))
+}