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From Carl Trieloff <cctriel...@redhat.com>
Subject Re: Flow control behavior of fanout exchange
Date Fri, 30 Oct 2009 15:11:37 GMT
Andy Li wrote:
> Hi,
> We ran into strange differences of flow control behavior of fanout exchange.
> We use configuration with one publisher and 10 subscribers.
> 1)On some machines, publisher throughput will be higher than subscriber
> throughput, and eventually the queue will overflow and throw an exception.
> This is, as I understand, the expected behavior - publisher has entire 1
> Gbit bandwidth to itself, whereas subscribers share it, so they have lower
> theoretical limit. We've coded a simple flow control scheme to manage this.

FYI, the broker also has a prublisher max rate config options which may 
help you.

> 2)However, on other machines we installed the broker, publisher and each
> subscriber throughput seem to move in sync. There is little buffering in the
> queue, and the overflow never happens. While the lack of overflow is
> convenient, bandwidth utilization is 2-4 times lower compared to broker
> machines exibiting behavior (1). In (1), combined output bandwidth utilized
> by subscribers is 80-90% of 1Gbit available. In (2), it's 20-40%, depending
> on the machine and latency to client.
> All broker machines use the same OS version and broker 0.5 binaries with
> default broker config. We can't figure out what is causing this difference
> in behavior. We did seem to induce behavior (2) on machines (1) by running
> unrelated workload concurrently that strongly competed for bandwidth.

Should like hardware or network, or it cold be things like cpuspeed 
running on one machine and
not the other etc...  Any more details on network, machines etc. That is 
where I would start looking.


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