[rabbitmq-discuss] Sequential message processing guarantee

[Yogesh Ketkar]

Hello Alex,

I thought, using default Connection con = factory.newConnection(),
ThreadPool which gets created will have more than one thread and
calling basicConsume will result in processing of messages on multiple
threads.

But if we explicitly provide Executors.newSingleThreadExecutor() to
newConnection method, only single thread will come into play with
basicConsume.

Is my understanding correct?

regards, Yogesh


On Jan 23, 7:48 pm, Alexandru Scvorţov <alexan... at rabbitmq.com> wrote:
> 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 <alexan... 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-disc... at lists.rabbitmq.com
> > > >https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss
>
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