In what order does (stand-alone) HornetQ Server distribute messages to multiple clients connected to the same queue?

[bruceas]

I have the following configuration:

- single, stand-alone HornetQ server

- single producer client regularly writing messages to a specific queue (e.g. "DEMO_QUEUE")

- multiple (10) consumer clients consuming messages from this same queue ("DEMO_QUEUE")

Every time the producer sends a message, it is delivered to one (and only one) consumer (as expected).

For any given message, how does HornetQ determine what particular consumer to send that message to?

In some small tests I've done, it seems that a "round-robin" algorithm (similar to the default one used with clusters) is used (perhaps based on the timing of the various connections?)

For example, consumer 1 will receive the first message, consumer 2 will receive the second message, consumer 3 the third message, etc;

After 10 messages are sent, the pattern continues (e.g. consumer 1 receives the 11th message, consumer 2 receives the 12th message, etc. etc).

If there any way to change this pattern? (for example, to deliver any given message to a "random" consumer, instead of the next consumer in line?)

I tried setting the <connection-load-balancing-policy-class-name> to org.hornetq.api.core.client.loadbalance.RandomConnectionLoadBalancingPolicy, but this didn't seem to affect anything (and the documentation suggests that this is only relevant when clusters are used).

Thanks

[gaohoward]

Yes it is round robin and it cannot be configured. The <connection-load-balancing-policy-class-name> doesn't work becaused it is used to control how a client creates connections to a hornetq cluster.

For your case I think you can use a Topic with 10 subscribers. each subscriber has a unique selector. On your producer side for each message you can set a property with a value that randomly picked up to match one of the selectors.

[bruceas]

Thank you very much, this answers my question!

Does the original order depend on when a client makes a connection? So if client 1 connects first, then client 2 connects 1 second later, then client 3 connects 1 second after that, will the order of the round-robin be 1-2-3-1-2-3, etc.?

Thanks again

[ataylor]

yes, but remember there are other factors that may come into play such as consumer flow control, consumer buffering etc.

[bruceas]

Understood. Thank you.