[Spread-users] Sending messages to a fixed set of servers

Ryan Caudy caudy at jhu.edu
Tue May 4 14:40:51 EDT 2004

This service seems like a kind of persistent messaging service. 
Services like this have been discussed on the list before, and there may 
be some sort of similar service implemented in the JMS4Spread project, 
but I don't know.  I don't see that it would be at all unreasonable to 
use Spread as the lower layer in such an architecture, though it would 
still be non-trivial.


Christian Schnell wrote:

> Hello,
> I came only recently across GCS in general and spread specifically, and 
> I'm really impressed by your substantiated and so valueable work, really 
> great.
> I'm posting here because I'm looking for a specific extension to spread, 
> here my sketchy requirements: A broadcast to a fixed set of servers, 
> hiding the fact that any subset may not be reachable at the moment.
> What I have in mind is a service that delivers a message not only to the 
> servers of a configuration (like spread) but eventually also to all 
> remaining servers of a fixed superset (it is assumed that later 
> configurations provide the missing network routes). That service should 
> hide the details of storing, tracking, exchanging and removing the 
> postponed messages (messages can be removed from the local storage as 
> soon as it can be concluded that they have been delivered globally).
> Under the hood, the service provides some sort of lazy replication to 
> synchronize the persistent message buffers of servers, all messages are 
> delivered in consistent order to applications:
> a) messages are delivered in the agreed order of their configuration,
> b) successive configurations are processed in their sequential order and
> c) non-sequential configurations in arbitrary order.
> I would imagine this service to inform the application twice about each 
> message: once on arrival of a message and once right before it is 
> discarded (when it is clear that it has been delivered to all servers), 
> that should perhaps be configurable with each single message. It might 
> also be usefull if the service would tag messages as being either 'live' 
> or 'replay' when delivering to the application.
> Now my questions regarding all this:
> - Do these requirements make sense to you? Has this been discussed here 
> before?
> - What would be the appropriate name for such a service?
> - Any objections to implementing this as a layer on top of spread?
> - Has this already been done with spread? Or with any other GCS?
> - Does it make sense to start such an effort with spread or are there 
> better ways to achive this?
> - Anything else to learn from?
> Thanks,
> Christian
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Ryan W. Caudy
Center for Networking and Distributed Systems
Department of Computer Science
Johns Hopkins University

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