[Spread-users] Unique message id

Yair Amir yairamir at cnds.jhu.edu
Sun Aug 11 04:58:02 EDT 2002


Hi,

The internal sequence numbers are unique within each daemon view in
the current protocols and their current implementation.
However, you have to remember that this may not have any effect on the
group membership. Therefore, if you use these internal counters,
the daemon membership can change without your group membership
changing (for example, a new daemon merged into the daemon membership
but this daemon currently has no processes connected with it).
In this case, your group will NOT see a membership event but the internal
counters will be reset to 1.

Therefore I think you cannot guarantee that this kind of a solution
will be correct.

If you could specify the service you are interested in then
there may be a correct (and cleaner) way to implement it.

  Cheers,

  :) Yair.


Sam> I am trying to add a special broadcast primitive into
Sam> spread, if the internal sequence numbers are unique
Sam> within each 'view' of the membership, they will be
Sam> fine to fit in the things that I am working on, thank
Sam> you :).


Sam> yisheng



Sam> --- Jonathan Stanton <jonathan at cnds.jhu.edu> wrote:
>> Hi,
>> 
>> The sequence numbers generated by Spread to order
>> messages are not
>> accessible to applications, so I'm not sure how you
>> were going to use
>> them. In actuality the internal sequence numbers are
>> unique within each
>> 'view' of the membership, but as soon as a daemon
>> crashes or restarts or
>> a network partition occurs or recoveres, the
>> sequence numbers will start
>> over at 1, so I don't think they will work for you.
>> 
>> The best way is to just tag your application level
>> messages with a unique
>> message id such as a tuple of local application
>> sequence number and
>> spread connection private name (which is guaranteed
>> to be unique until
>> your application disconnects) or some other 'name'
>> attached to each
>> instance of your application.
>> 
>> Jonathan
>> 
>> On Fri, Aug 09, 2002 at 02:50:23PM -0400, Sam Liu
>> wrote:
>> > Hi,
>> > 
>> > I would need to attach a message id to each
>> message
>> > delivered to the applications. I am considering to
>> use
>> > the seq no of the last packet of the message as
>> the
>> > message id. Is the seq no of the packet grobally
>> > unique in a specific configuration? Thanks.
>> > 
>> > 
>> > yisheng
>> > 
>> > McGill U
>> > Canada
>> 
>> -- 
>>
Sam> -------------------------------------------------------
>> Jonathan R. Stanton         jonathan at cs.jhu.edu
>> Dept. of Computer Science   
>> Johns Hopkins University    
>>
Sam> -------------------------------------------------------
>> 
>> _______________________________________________
>> Spread-users mailing list
>> Spread-users at lists.spread.org
>>
Sam> http://lists.spread.org/mailman/listinfo/spread-users


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