[rabbitmq-discuss] Producers hanging when reaching high memory watermark on 1.8.1
Alister.Morton at tradition.com
Mon Aug 16 15:01:34 BST 2010
> The memory condition that triggered channel.flow can clear just as
> quickly as any condition that caused a slow down.
Indeed so. In which case the stop would be removed.
I haven't looked closely at flow control; I'm possibly somewhat naively assuming that the broker sends distinct "xon/xoff" type messages to the client, rather than passively implementing flow control by simply not dequeueing data.
In the case of xon/xoff style flow control, then "stopped" is a distinct finite state and is precisely detectable (and I think it should be. If the spec doesn't allow for this then I'd say it's an omission but c'est la vie). In the case of passive flow control it's not really deterministic and you have to implement some sort of empirical "Well it /looks/ like it's stopped but who knows" fuzzy logic.
A bit like a turnpike that is clogged but moving very slowly - all you know it appears to be open so you have to make a value judgement on whether it's likely, on balance, to be worth it to join the slow traffic or to give up and find an alternative route. OTOH, if the road is closed, you KNOW with certainty that you have to look elsewhere.
One is a fuzzy best guess based on observations and inference, one is a state based decision.
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