[rabbitmq-discuss] Queue Clustering and Sequencing

Roger Fischer Roger.Fischer at abb.ventyx.com
Mon Oct 24 21:05:40 BST 2011



I am curious if RabbitMQ addresses the following use case.


A single queue. Persistent.


A producer creates messages fast (average 10 msg/sec).


Consumers process messages slow (average 1 msg/sec). Thus 10 consumers
are required to keep up.


Challenge 1: Some messages (< 1%) are related and need to be processed
in order. If two dependent messages are less than 10 messages apart,
they are processed in parallel. That's a problem.


Obvious solution: create 10 queues, each with a different key, and each
with only one consumer. But:

* Non-related messages are unnecessarily sequenced. When the key
distribution is not exactly even, one queue may have a backup while
another is idle.

* Complex to configure for differently sized systems.


Challenge 1+: earlier message could fail processing and be re-queued
with a delay. Obvious solution doesn't fix that.


Desired solution: Queue knows what messages are being processed /
re-queued and holds messages with the same key.


But that's not all. Consumers are clustered, with load balancing
(scalability) and failover (availability).


Challenge 2a: related messages must still be processed by the same
consumer (and thus loadbalanced to the same node).


Challenge 2b: related messages must be processed in order across node


Obvious solution: Solution to 1 and migrate file store and consumer from
failed node to another node. But:

* Need external system to manage migration.

* Very complex to configure for differently sized systems (different
workloads, different node sizes and different cluster sizes).


Desired solution: Solution 1 queues, and coordinate across nodes what
keys have messages being processed or re-queued. Will affect throughput
(we need only 250 msg/sec).






PS: Please copy the response to my email (roger dot fischer at abb dot
Ventyx dot com) as I am not a subscriber of the list.


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