Refactor shadow WAL to use segments

db.go

@@ -233,10 +233,6 @@ func (db *DB) invalidate(ctx context.Context) (err error) {
 	if err := db.invalidatePos(ctx); err != nil {
 		return fmt.Errorf("cannot determine pos: %w", err)
 	} else if db.pos.IsZero() {
-		db.Logger.Printf("init: no wal files available, clearing generation")
-		if err := db.clearGeneration(ctx); err != nil {
-			return fmt.Errorf("clear generation: %w", err)
-		}
 		return nil // no position, exit
 	}
 
@@ -263,7 +259,7 @@ func (db *DB) invalidatePos(ctx context.Context) error {
 	}
 	defer itr.Close()
 
-	var pos Pos
+	pos := Pos{Generation: generation}
 	for itr.Next() {
 		info := itr.WALSegment()
 		pos = info.Pos()
@@ -621,14 +617,14 @@ func (db *DB) init() (err error) {
 
 	// Determine current position, if available.
 	if err := db.invalidate(db.ctx); err != nil {
-		return fmt.Errorf("invalidate: %w", err)
+		return fmt.Errorf("cannot determine position: %w", err)
 	}
 
 	// If we have an existing shadow WAL, ensure the headers match.
 	if err := db.verifyHeadersMatch(); err != nil {
 		db.Logger.Printf("init: cannot determine last wal position, clearing generation; %s", err)
-		if err := db.clearGeneration(db.ctx); err != nil {
+		if err := os.Remove(db.GenerationNamePath()); err != nil && !os.IsNotExist(err) {
-			return fmt.Errorf("clear generation: %w", err)
+			return fmt.Errorf("remove generation name: %w", err)
 		}
 	}
 
@@ -645,13 +641,6 @@ func (db *DB) init() (err error) {
 	return nil
 }
 
-func (db *DB) clearGeneration(ctx context.Context) error {
-	if err := os.Remove(db.GenerationNamePath()); err != nil && !os.IsNotExist(err) {
-		return err
-	}
-	return nil
-}
-
 // verifyHeadersMatch returns true if the primary WAL and last shadow WAL header match.
 func (db *DB) verifyHeadersMatch() error {
 	// Skip verification if we have no current position.
@@ -719,18 +708,18 @@ func (db *DB) cleanWAL(ctx context.Context) error {
 	}
 
 	// Determine lowest index that's been replicated to all replicas.
-	minIndex := -1
+	var min Pos
 	for _, r := range db.Replicas {
 		pos := r.Pos().Truncate()
 		if pos.Generation != generation {
 			continue // different generation, skip
-		} else if minIndex == -1 || pos.Index < minIndex {
+		} else if min.IsZero() || pos.Index < min.Index {
-			minIndex = pos.Index
+			min = pos
 		}
 	}
 
 	// Skip if our lowest position is too small.
-	if minIndex <= 0 {
+	if min.IsZero() {
 		return nil
 	}
 
@@ -745,11 +734,11 @@ func (db *DB) cleanWAL(ctx context.Context) error {
 		index, err := ParseIndex(ent.Name())
 		if err != nil {
 			continue
-		} else if index >= minIndex {
+		} else if index >= min.Index {
 			continue // not below min, skip
 		}
 
-		if err := os.RemoveAll(filepath.Join(dir, FormatIndex(index))); err != nil {
+		if err := os.RemoveAll(filepath.Join(dir)); err != nil {
 			return err
 		}
 

replica.go

@@ -515,7 +515,7 @@ func (r *Replica) Snapshot(ctx context.Context) (info SnapshotInfo, err error) {
 		return info, err
 	}
 
-	r.Logger.Printf("snapshot written %s/%08x", pos.Generation, pos.Index)
+	log.Printf("snapshot written %s/%08x", pos.Generation, pos.Index)
 
 	return info, nil
 }