Fix rollover issue under load

db.go

@@ -441,7 +441,7 @@ func (db *DB) Sync() (err error) {
 
 	// Issue the checkpoint.
 	if checkpoint {
-		if err := db.checkpoint(forceCheckpoint); err != nil {
+		if err := db.checkpoint(info, forceCheckpoint); err != nil {
 			return fmt.Errorf("checkpoint: force=%v err=%w", err)
 		}
 	}
@@ -514,20 +514,13 @@ func (db *DB) verify() (info syncInfo, err error) {
 		return info, nil
 	}
 
-	// Compare WAL headers. Ensure that checkpoint sequences match and the
-	// header is the same or that we have moved to the next sequence. If we have
-	// out-of-order or skipped checkpoint sequences then we should start a new
-	// generation.
+	// Compare WAL headers. Start a new shadow WAL if they are mismatched.
 	if hdr0, err := readWALHeader(db.WALPath()); err != nil {
 		return info, fmt.Errorf("cannot read wal header: %w", err)
 	} else if hdr1, err := readWALHeader(info.shadowWALPath); err != nil {
 		return info, fmt.Errorf("cannot read shadow wal header: %w", err)
-	} else if seq0, seq1 := readCheckpointSeqNo(hdr0), readCheckpointSeqNo(hdr1); seq0 == seq1 && !bytes.Equal(hdr0, hdr1) {
-		return info, fmt.Errorf("wal header mismatch: chkpt=%d", seq0)
-	} else if seq0+1 == seq1 {
+	} else if !bytes.Equal(hdr0, hdr1) {
 		info.restart = !bytes.Equal(hdr0, hdr1)
-	} else if seq0 != seq1 {
-		return info, fmt.Errorf("non-contiguous checkpoint sequence: real=%d shadow=%d", seq0, seq1)
 	}
 
 	// TODO: Handle checkpoint sequence number rollover.
@@ -730,7 +723,13 @@ func readLastChecksumFrom(f *os.File, pageSize int) (uint32, uint32, error) {
 }
 
 // checkpoint performs a checkpoint on the WAL file.
-func (db *DB) checkpoint(force bool) error {
+func (db *DB) checkpoint(info syncInfo, force bool) error {
+	// Read WAL header before checkpoint to check if it has been restarted.
+	hdr, err := readWALHeader(db.WALPath())
+	if err != nil {
+		return err
+	}
+
 	// Ensure the read lock has been removed before issuing a checkpoint.
 	// We defer the re-acquire to ensure it occurs even on an early return.
 	if err := db.releaseReadLock(); err != nil {
@@ -759,6 +758,31 @@ func (db *DB) checkpoint(force bool) error {
 	if err := db.acquireReadLock(); err != nil {
 		return fmt.Errorf("release read lock: %w", err)
 	}
+
+	if _, err = db.db.Exec(`INSERT INTO _litestream_seq (id, seq) VALUES (1, 1) ON CONFLICT (id) DO UPDATE SET seq = seq + 1`); err != nil {
+		return err
+	}
+
+	// If WAL hasn't been restarted, exit.
+	if other, err := readWALHeader(db.WALPath()); err != nil {
+		return err
+	} else if bytes.Equal(hdr, other) {
+		return nil
+	}
+
+	// Parse index of current shadow WAL file.
+	dir, base := filepath.Split(info.shadowWALPath)
+	index, err := ParseWALFilename(base)
+	if err != nil {
+		return 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))
+	if err := db.initShadowWALFile(newShadowWALPath); err != nil {
+		return fmt.Errorf("cannot init shadow wal file: name=%s err=%w", newShadowWALPath, err)
+	}
+
 	return nil
 }