[Spread-users] max number of groups and max length of group name

Ryan Caudy caudy at jhu.edu
Thu Mar 4 11:11:06 EST 2004


Spread can scale well to many thousands of groups.  There is no maximum 
in terms of what the code can handle -- the constraint is memory size. 
In terms of performance impact of having a large number of groups, there 
are two considerations: (1)For simple message delivery, the list is 
searched (for each non-private group the message is sent to) at a cost 
of one lookup in a skiplist that stores all the groups information... 
so, expected lg(n) time;  (2)After a daemon membership change, there may 
be additional computational and network costs incurred per-group.

The maximum length of a group name can be increased.  You'll need to 
change the header files spread_params.h (for daemon code's information) 
and sp.h (for the library code).  A recompile will, of course, be 
needed.  Some people have run into bus errors after doing this, but as 
far as I know this is fixed in CVS and should be out with 3.17.2.  In 
terms of performance, there will be higher memory and network usage for 
group names, proportional to the change you make.  Lookup to deliver 
messages might take slightly longer, but I doubt that this will be a 
significant cost (unless you make the names huge).  If you send to lots 
of groups, you might cause messages to be split more often by the 
network layers of spread (or at the lower level, by routers)... also, 
more internal spread messages may be necessary during daemon membership 


Jim Vickroy wrote:

> Good day,
> I apologize if these questions have been previously answered, but I was
> unable to download the mailing list archive (page not available).
> I have the following questions:
> (1) What is the maximum number of simultaneous groups that Spread can
> accomodate?
> (2) Can the maximum length of a group name be increased beyond the
> 32-character limit?  If so, how?  Recompile?  Are there adverse impacts on
> performance of doing so?
> Thanks for you assistnece,
> jim vickroy
> _______________________________________________
> Spread-users mailing list
> Spread-users at lists.spread.org
> http://lists.spread.org/mailman/listinfo/spread-users

Ryan W. Caudy
Center for Networking and Distributed Systems
Department of Computer Science
Johns Hopkins University

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