Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

{
    if (!use_marks_file || marks_loaded)
        return;
    
    
    WriteLock lock{rwlock, lock_timeout};
    if (!lock)
        throw Exception("Lock timeout exceeded", ErrorCodes::TIMEOUT_EXCEEDED);
    loadMarks(lock);
}
void StorageLog::loadMarks(const WriteLock & lock )