broker: limit total queued messages, not just per client

[Karl Palsson]

Currently (1.1.x) mosquitto broker allows configuration of the maximum number of outstanding messages that are queued per client. For resource constrained systems, this is not really good enough, as there's no way to limit the number of clients. Further, there's no way to control the size of messages. (500 queued 2 byte messages are pretty cheap, 500 queued 1meg messages are not at all cheap)

Ideally, we would be able to limit the total amount of memory used for storing queued messages.
Alternatively, or even better for some users perhaps, would be to limit the total number of messages for the entire broker, not just the number of messages per client.

[Roger Light (roger.light)]

You can limit clients with "max_connections" by the way. Other points are valid.

[Roger Light (roger.light)]

Hi there,

I'm migrating bugs to Eclipse. The new url for this bug is:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=452919