Group WAL files in file replica

db.go

@@ -129,7 +129,7 @@ func (db *DB) CurrentShadowWALIndex(generation string) (int, error) {
 		if !strings.HasSuffix(fi.Name(), WALExt) {
 			continue
 		}
-		if v, err := ParseWALFilename(filepath.Base(fi.Name())); err != nil {
+		if v, _, _, err := ParseWALPath(fi.Name()); err != nil {
 			continue // invalid wal filename
 		} else if v > index {
 			index = v
@@ -640,13 +640,13 @@ func (db *DB) syncWAL(info syncInfo) (newSize int64, err error) {
 
 	// Parse index of current shadow WAL file.
 	dir, base := filepath.Split(info.shadowWALPath)
-	index, err := ParseWALFilename(base)
+	index, _, _, err := ParseWALPath(base)
 	if err != nil {
 		return 0, fmt.Errorf("cannot parse shadow wal filename: %s", base)
 	}
 
 	// Start a new shadow WAL file with next index.
-	newShadowWALPath := filepath.Join(dir, FormatWALFilename(index+1))
+	newShadowWALPath := filepath.Join(dir, FormatWALPath(index+1))
 	if err := db.initShadowWALFile(newShadowWALPath); err != nil {
 		return 0, fmt.Errorf("cannot init shadow wal file: name=%s err=%w", newShadowWALPath, err)
 	}
@@ -962,14 +962,13 @@ func (db *DB) checkpoint(info syncInfo, force bool) error {
 	}
 
 	// Parse index of current shadow WAL file.
-	dir, base := filepath.Split(info.shadowWALPath)
+	index, _, _, err := ParseWALPath(info.shadowWALPath)
-	index, err := ParseWALFilename(base)
 	if err != nil {
-		return fmt.Errorf("cannot parse shadow wal filename: %s", base)
+		return fmt.Errorf("cannot parse shadow wal filename: %s", info.shadowWALPath)
 	}
 
 	// Start a new shadow WAL file with next index.
-	newShadowWALPath := filepath.Join(dir, FormatWALFilename(index+1))
+	newShadowWALPath := filepath.Join(filepath.Dir(info.shadowWALPath), FormatWALPath(index+1))
 	if err := db.initShadowWALFile(newShadowWALPath); err != nil {
 		return fmt.Errorf("cannot init shadow wal file: name=%s err=%w", newShadowWALPath, err)
 	}

litestream.go

@@ -119,19 +119,6 @@ func readFileAt(filename string, offset, n int64) ([]byte, error) {
 	return buf, nil
 }
 
-func ParseWALFilename(name string) (index int, err error) {
-	v, err := strconv.ParseInt(strings.TrimSuffix(name, WALExt), 16, 64)
-	if err != nil {
-		return 0, fmt.Errorf("invalid wal filename: %q", name)
-	}
-	return int(v), nil
-}
-
-func FormatWALFilename(index int) string {
-	assert(index >= 0, "wal index must be non-negative")
-	return fmt.Sprintf("%016x%s", index, WALExt)
-}
-
 // removeTmpFiles recursively finds and removes .tmp files.
 func removeTmpFiles(root string) error {
 	return filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
@@ -167,6 +154,8 @@ func IsSnapshotPath(s string) bool {
 // ParseSnapshotPath returns the index for the snapshot.
 // Returns an error if the path is not a valid snapshot path.
 func ParseSnapshotPath(s string) (index int, typ, ext string, err error) {
+	s = filepath.Base(s)
+
 	a := snapshotPathRegex.FindStringSubmatch(s)
 	if a == nil {
 		return 0, "", "", fmt.Errorf("invalid snapshot path: %s", s)
@@ -186,6 +175,8 @@ func IsWALPath(s string) bool {
 // ParseWALPath returns the index & offset for the WAL file.
 // Returns an error if the path is not a valid snapshot path.
 func ParseWALPath(s string) (index int, offset int64, ext string, err error) {
+	s = filepath.Base(s)
+
 	a := walPathRegex.FindStringSubmatch(s)
 	if a == nil {
 		return 0, 0, "", fmt.Errorf("invalid wal path: %s", s)
@@ -196,6 +187,19 @@ func ParseWALPath(s string) (index int, offset int64, ext string, err error) {
 	return int(i64), int64(off64), a[3], nil
 }
 
+// FormatWALPath formats a WAL filename with a given index.
+func FormatWALPath(index int) string {
+	assert(index >= 0, "wal index must be non-negative")
+	return fmt.Sprintf("%016x%s", index, WALExt)
+}
+
+// FormatWALPathWithOffset formats a WAL filename with a given index & offset.
+func FormatWALPathWithOffset(index int, offset int64) string {
+	assert(index >= 0, "wal index must be non-negative")
+	assert(offset >= 0, "wal offset must be non-negative")
+	return fmt.Sprintf("%016x_%016x%s", index, offset, WALExt)
+}
+
 var walPathRegex = regexp.MustCompile(`^([0-9a-f]{16})(?:_([0-9a-f]{16}))?(.wal(?:.gz)?)$`)
 
 // isHexChar returns true if ch is a lowercase hex character.

replicator.go

@@ -10,7 +10,7 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
-	"strings"
+	"strconv"
 	"sync"
 	"time"
 )
@@ -51,6 +51,17 @@ type Replica interface {
 	WALReader(ctx context.Context, generation string, index int) (io.ReadCloser, error)
 }
 
+// GenerationStats represents high level stats for a single generation.
+type GenerationStats struct {
+	// Count of snapshot & WAL files.
+	SnapshotN int
+	WALN      int
+
+	// Time range for the earliest snapshot & latest WAL file update.
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
+
 var _ Replica = (*FileReplica)(nil)
 
 // FileReplica is a replica that replicates a DB to a local file path.
@@ -104,9 +115,52 @@ func (r *FileReplica) WALDir(generation string) string {
 	return filepath.Join(r.dst, "generations", generation, "wal")
 }
 
+// WALSubdir returns the directory used for grouping WAL files.
+func (r *FileReplica) WALSubdir(generation string, index int) string {
+	return filepath.Join(r.WALDir(generation), fmt.Sprintf("%016x", uint64(index)&walDirMask))
+}
+
+// WALSubdirNames returns a list of all WAL subdirectory group names.
+func (r *FileReplica) WALSubdirNames(generation string) ([]string, error) {
+	fis, err := ioutil.ReadDir(r.WALDir(generation))
+	if err != nil && !os.IsNotExist(err) {
+		return nil, err
+	}
+
+	var names []string
+	for _, fi := range fis {
+		if _, err := strconv.ParseUint(fi.Name(), 16, 64); err != nil {
+			continue
+		}
+		names = append(names, fi.Name())
+	}
+	return names, nil
+}
+
+// MaxWALSubdirName returns the highest WAL subdirectory group name.
+func (r *FileReplica) MaxWALSubdirName(generation string) (string, error) {
+	fis, err := ioutil.ReadDir(r.WALDir(generation))
+	if err != nil {
+		return "", err
+	}
+
+	var name string
+	for _, fi := range fis {
+		if _, err := strconv.ParseUint(fi.Name(), 16, 64); err != nil {
+			continue
+		} else if name == "" || fi.Name() > name {
+			name = fi.Name()
+		}
+	}
+	if name == "" {
+		return "", os.ErrNotExist
+	}
+	return name, nil
+}
+
 // WALPath returns the path to a WAL file.
 func (r *FileReplica) WALPath(generation string, index int) string {
-	return filepath.Join(r.WALDir(generation), fmt.Sprintf("%016x.wal", index))
+	return filepath.Join(r.WALSubdir(generation, index), fmt.Sprintf("%016x.wal", index))
 }
 
 // Generations returns a list of available generation names.
@@ -184,7 +238,13 @@ func (r *FileReplica) snapshotStats(generation string) (n int, min, max time.Tim
 }
 
 func (r *FileReplica) walStats(generation string) (n int, min, max time.Time, err error) {
-	fis, err := ioutil.ReadDir(r.WALDir(generation))
+	names, err := r.WALSubdirNames(generation)
+	if err != nil {
+		return n, min, max, err
+	}
+
+	for _, name := range names {
+		fis, err := ioutil.ReadDir(filepath.Join(r.WALDir(generation), name))
 		if os.IsNotExist(err) {
 			return n, min, max, nil
 		} else if err != nil {
@@ -205,14 +265,8 @@ func (r *FileReplica) walStats(generation string) (n int, min, max time.Time, er
 				max = modTime
 			}
 		}
-	return n, min, max, nil
 	}
-
+	return n, min, max, nil
-type GenerationStats struct {
-	SnapshotN int
-	WALN      int
-	CreatedAt time.Time
-	UpdatedAt time.Time
 }
 
 // Start starts replication for a given generation.
@@ -305,9 +359,16 @@ func (r *FileReplica) pos() (pos Pos, err error) {
 	}
 	pos.Generation = generation
 
+	// Find highest WAL subdirectory group.
+	subdir, err := r.MaxWALSubdirName(generation)
+	if os.IsNotExist(err) {
+		return pos, nil // no replicated wal, start at beginning of generation
+	} else if err != nil {
+		return pos, err
+	}
+
 	// Find the max WAL file.
-	dir := r.WALDir(generation)
+	fis, err := ioutil.ReadDir(filepath.Join(r.WALDir(generation), subdir))
-	fis, err := ioutil.ReadDir(dir)
 	if os.IsNotExist(err) {
 		return pos, nil // no replicated wal, start at beginning of generation
 	} else if err != nil {
@@ -316,17 +377,10 @@ func (r *FileReplica) pos() (pos Pos, err error) {
 
 	index := -1
 	for _, fi := range fis {
-		name := fi.Name()
+		if idx, _, _, err := ParseWALPath(fi.Name()); err != nil {
-		name = strings.TrimSuffix(name, ".gz")
-
-		if !strings.HasSuffix(name, WALExt) {
-			continue
-		}
-
-		if v, err := ParseWALFilename(filepath.Base(name)); err != nil {
 			continue // invalid wal filename
-		} else if index == -1 || v > index {
+		} else if index == -1 || idx > index {
-			index = v
+			index = idx
 		}
 	}
 	if index == -1 {
@@ -335,7 +389,7 @@ func (r *FileReplica) pos() (pos Pos, err error) {
 	pos.Index = index
 
 	// Determine current offset.
-	fi, err := os.Stat(filepath.Join(dir, FormatWALFilename(pos.Index)))
+	fi, err := os.Stat(r.WALPath(pos.Generation, pos.Index))
 	if err != nil {
 		return pos, err
 	}
@@ -446,8 +500,7 @@ func (r *FileReplica) syncNext(ctx context.Context, pos Pos) (_ Pos, err error)
 
 // compress gzips all WAL files before the current one.
 func (r *FileReplica) compress(ctx context.Context, generation string) error {
-	dir := r.WALDir(generation)
+	filenames, err := filepath.Glob(filepath.Join(r.WALDir(generation), "**/*.wal"))
-	filenames, err := filepath.Glob(filepath.Join(dir, "*.wal"))
 	if err != nil {
 		return err
 	} else if len(filenames) <= 1 {
@@ -513,14 +566,23 @@ func (r *FileReplica) SnapshotIndexAt(ctx context.Context, generation string, ti
 // Returns the highest index for a WAL file that occurs before timestamp.
 // If timestamp is zero, returns the highest WAL index.
 func (r *FileReplica) WALIndexAt(ctx context.Context, generation string, timestamp time.Time) (int, error) {
-	fis, err := ioutil.ReadDir(r.WALDir(generation))
+	names, err := r.WALSubdirNames(generation)
+	if err != nil {
+		return 0, err
+	}
+
+	// TODO: Optimize to only read the last group if no timestamp specified.
+	// TODO: Perform binary search to find correct timestamp.
+
+	var index int
+	for _, name := range names {
+		fis, err := ioutil.ReadDir(filepath.Join(r.WALDir(generation), name))
 		if os.IsNotExist(err) {
 			return 0, nil
 		} else if err != nil {
 			return 0, err
 		}
 
-	index := -1
 		for _, fi := range fis {
 			// Read index from snapshot filename.
 			idx, _, _, err := ParseWALPath(fi.Name())
@@ -534,10 +596,8 @@ func (r *FileReplica) WALIndexAt(ctx context.Context, generation string, timesta
 
 			index = idx
 		}
-
-	if index == -1 {
-		return 0, nil
 	}
+
 	return index, nil
 }
 
@@ -638,3 +698,9 @@ func compressFile(src, dst string) error {
 	// Move compressed file to final location.
 	return os.Rename(dst+".tmp", dst)
 }
+
+// walDirMask is a mask used to group 64K wal files into a directory.
+const (
+	walDirFileN = 0x10000
+	walDirMask  = uint64(0xFFFFFFFFFFFFFFFF ^ (walDirFileN - 1))
+)