[rabbitmq-discuss] Order in Queues (FIFO)

[Michael Klishin]

On oct 4, 2013, at 3:54 p.m., rabbit15 <bison_art at o2.pl> wrote:

> eq. payload sent to rabbit in in order - line: 3, 4, 5
> but receiving is in order line: 6(same msg as 4), 7(same message as 5), 8
> (same message as 3) - which gives payloads order 4,5,3 

RabbitMQ queues are FIFO but there are several factors that
you need to take into account:

 * Messages can be requeued
 * There can be multiple consumers per queue
 * Multiple messages can be pushed to a consumer in rapid succession.
   Deliveries can be dispatched in a thread pool and processed concurrently (this is indeed what several popular clients do)

What code produced the log above? Printing to stdout is not a very reliable way
when it comes to determining the order. Updating a synchronized collection
of some kind and inspecting it is a more reliable way.

MK



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