truncate method
Implementation
Future<void> truncate() async {
if (_closed) return;
await _flush();
await _raf.close();
final file = File(path);
final rec = WalRecord(
op: WalOp.checkpoint,
table: '_global',
payload: {'lsn': _lsn, 'ts': DateTime.now().millisecondsSinceEpoch},
lsn: _lsn,
txnId: 0,
checksum: 0,
);
await file.writeAsString('${rec.encode()}\n');
_raf = await file.open(mode: FileMode.append);
await _flush();
}