For Ayende

MemoryMapPager.cs

public MemoryMapPager(string fileName, FlushMode flushMode = FlushMode.Full)
{
    _flushMode = flushMode;
    
    var fileInfo = new FileInfo(fileName);
    var fileLength = fileInfo.Length;
    var isFileEmpty = fileLength == 0 || fileInfo.Exists == false;

    _fileStream = fileInfo.Open(FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.Read);

    _allocatedPages = isFileEmpty ? 0 : (long) Math.Ceiling((float) fileLength/PageSize);
}