[rabbitmq-discuss] Sequential message processing guarantee

[Alexandru Scvorţov]

Hi Yogesh,

> using channel.basicConsume on the channel which is created like this
> ExecutorService es = Executors.newSingleThreadExecutor();
> Connection connection = factory.newConnection(es);
> final Channel channel = connection.createChannel();
> 
> is probably a better approach.
> Any comments on this?

I don't quite see the point of the ExecutorService.

Just doing this:

> Connection connection = factory.newConnection(es);
> final Channel channel = connection.createChannel();

Then, calling basicConsume with your own subclass of DefaultConsumer
should be fine.

Cheers,
Alex

On Mon, Jan 23, 2012 at 08:08:37PM +0530, Yogesh Ketkar wrote:
> Thanks Alex.
> 
> I think, for sequential message processing, rather than this pattern
> while(true) {
>     GetResponse res = channel.basicGet(QUEUE_NAME, false);
>     if(res != null) {
>         // process and ack message
>    }
> }
> 
> using channel.basicConsume on the channel which is created like this
> ExecutorService es = Executors.newSingleThreadExecutor();
> Connection connection = factory.newConnection(es);
> final Channel channel = connection.createChannel();
> 
> is probably a better approach.
> Any comments on this?
> 
> regards, Yogesh
> 
> 2012/1/23 Alexandru Scvorţov <alexandru at rabbitmq.com>
> 
> > Hi Yogesh,
> >
> > In the absence of consumer failures, RabbitMQ will deliver messages from
> > a queue in order.
> >
> > So, if messages 1, 2, 3 reach a queue in order, RabbitMQ will deliver
> > them to consumers in the same order (1, 2, 3).
> >
> > But, if consumers fail before acknowledging the messages (or if they
> > reject the messages), those messages will requeued at the end of the
> > queue.  So, if the consumer that got message 1 rejects it, the new
> > order of messages will be 2, 3, 1.
> >
> > This all deals with message *delivery*.
> >
> > > There are multiple consumer threads consuming the messages.
> > > Though multiple threads are consuming the messages, I observed that
> > > messages still get processed sequentially.
> > > Is that the case and if NOT, what is the way to guarantee sequential
> > > processing of messages on one queue?
> >
> > The library makes no guarantees about the order in which you process
> > messages, only about the order in which they're delivered.
> >
> > If you want to process all the messages on a queue in order, only
> > consume from one thread (doing basic.get from one thread like you
> > suggested in the other email would work, but would also be highly
> > inefficient).
> >
> > Does this answer your question?
> >
> > Cheers,
> > Alex
> >
> > On Sun, Jan 22, 2012 at 09:38:40AM -0800, Yogesh Ketkar wrote:
> > > Running the code below, gives
> > > channel.basicConsume(QUEUE_NAME, autoAck, CONSUMER_TAG,
> > >       new DefaultConsumer(channel)  {
> > >         @Override
> > >         public void handleDelivery(String consumerTag, Envelope
> > > envelope, BasicProperties properties, byte[] body) {
> > >                 System.out.println(Thread.currentThread().getName());
> > >          }
> > > }
> > >
> > > o/p like
> > > pool-1-thread-1
> > > pool-1-thread-2
> > > pool-1-thread-3
> > > etc
> > >
> > > There are multiple consumer threads consuming the messages.
> > > Though multiple threads are consuming the messages, I observed that
> > > messages still get processed sequentially.
> > > Is that the case and if NOT, what is the way to guarantee sequential
> > > processing of messages on one queue?
> > >
> > > regards, Yogesh
> > >
> > > _______________________________________________
> > > rabbitmq-discuss mailing list
> > > rabbitmq-discuss at lists.rabbitmq.com
> > > https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss
> >