Journaler.cs

public class Journaler : IEventHandler<BufferEntry>
{
    private BufferEntry[] _buffer = new BufferEntry[1024];
    private int _current;
    private IJournalWriter _journal;

    public Journaler(IJournalWriter journal)
    {
        _journal = journal;
    }

    public void OnNext(BufferEntry data, long sequence, bool endOfBatch)
    {
        _buffer[_current++] = data;
        if (endOfBatch) Process();
    }

    private void Process()
    {
        var commands = _buffer.Take(_current).Select(e => e.Transaction as Command);
        _journal.AppendAsync(commands).Wait();
        _current = 0;
    }

}