[rabbitmq-discuss] How to handle full exchange history delivery

Wed Jun 1 14:43:58 BST 2011

That’s what I thought as well, although I’m thinking about a couple of issues about it:

·         Lack of knowledge about Erlang, which is the language I’d have to use to build a custom exchange, I guess

·         Amount of memory it would require to store the entire history in memory. It needn’t be in memory actually, but I’m not sure what would be the recommended way if the storage has to be carried out by exchange itself. Mnesia perhaps, would it make sense?
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Simone Busoli
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From: Jon Brisbin [mailto:jon at jbrisbin.com]
Sent: Wednesday, June 01, 2011 3:38 PM
To: Busoli, Simone
Cc: rabbitmq-discuss at lists.rabbitmq.com
Subject: Re: [rabbitmq-discuss] How to handle full exchange history delivery

I've been seriously considering adding this functionality to the Riak-backed custom exchange. It was something I thought I would add first time through but didn't.

You'd have to use a custom exchange. Not sure if that's an issue in your scenario or not.

Thanks!

Jon Brisbin
http//jbrisbin.com

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From: "Simone Busoli" <Simone.Busoli at ferrari.com>
To: rabbitmq-discuss at lists.rabbitmq.com
Sent: Wednesday, June 1, 2011 5:52:24 AM
Subject: [rabbitmq-discuss] How to handle full exchange history delivery

Hi,

I am trying to achieve a scenario in which messages are published from some data source into a RabbitMQ exchange and clients should be able to receive the full history of messages flown through that exchange, regardless of the exact moment in time when they connect.

I’ve been thinking to solve it by setting up a proxy which subscribes to the exchange where messages are published using its own queue, keeps an internal storage of the messages and accepts requests from clients.
When a request from a client arrives it just replays the full message history to the client by publishing the messages to the client queue (supplied in the ReplyTo field), then binds the client queue to the messages exchange, so that the client from this moment onwards starts receiving the “live” messages, and is pretty much unaware of what’s happened; it simply just receives the whole history.

Now I am under the impression that there’s a fundamental flaw in this reasoning, since the proxy cannot know when the message history has completed and he can switch the client to the live stream, because while it is replaying historical messages to the client other live messages might be arriving on the proxy’s queue, thus getting into an endless loop.

I’m probably missing something obvious, any advice about how others would approach this scenario is appreciated.

Simone

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