[rabbitmq-discuss] Java client notifications when basicPublish is throttled due to disk_free_limit

Tue Feb 19 21:20:49 GMT 2013

On 19/02/13 18:21, Joshua Crean wrote:
> Is there any way for the rabbit java client code to provide some type of
> notification when basicPublish is being throttled due to the
> disk_free_limit? Also, where do these un-published messages end up?
> We've tried to use rabbitmqctl to inspect the state of the
> queues/exchanges/channels, but the messages don't appear in any of these.

Throttling is behaviourally equivalent to network congestion. The 
messages are buffered in the network, until those buffers fill up, at 
which point the sender will block.

If, for example, connections were blocked due to lack of disk space and 
the server suddenly regained some disk space then all the messages 
published by clienta while connections were blocked will flow into the 
server and be processed.

> We are concerned about the potential to lose messages that the java code
> thinks it published successfully.

So presumably you are not *just* concerned about connection blocking due 
to disk space.

The general mechanism for dealing with potential message loss on 
publishing is 'confirms'. Now, while connections are blocked, no 
confirms for messages buffered in the network will be sent to clients. 
But, as noted above, the messages aren't actually lost. Potential loss 
will only occur when the connection gets terminated. At which point the 
safe assumption on the publisher side is that any messages which hasn't 
been confirmed may have been lost.

Matthias.