[Spread-users] maximum number of spread segments

[Ryan Caudy]

Hi,

There shouldn't be stability issues.  However, the more segments you use 
(especially on the wide area), the greater the chance of having 
performance problems.  People we know of have done surprisingly well in 
the past with 6 wide area sites, if I recall correctly, but the open 
source version of Spread isn't really designed to handle this well. 
Someone else might be better able to give you an idea of the performance 
they've had.

The issue is that segments are multicast/broadcast domains -- Spread is 
designed best to be extremely efficient within a segment.  However, when 
communicating with members of another segment, it has to send data via 
unicast to each member.  Recall also that each message must reach every 
single daemon in order for Spread's ordering guarantees to be met 
(because ordering is done across groups).  Thus you could be doing quite 
a lot of wide area communication if you have many segments with many 
daemons.

So, the answer to whether or not you'll have performance problems is 
that it depends on your network topology and message load.  On a fast 
switched LAN, you might do fine with a large number of small segments, 
if you don't need to send a lot of messages.

Cheers,
Ryan

G. Naik wrote:

> Hey all,
> 
> I'm interested in understanding why the number of segments is limited to 
> 20 (MAX_SEGMENTS in spread_params.h).  Are there any ill effects 
> (performance/stability issues) in increasing this value?
> 
> (This may have been discussed before, but I couldn't find the relevant 
> threads in the archives).
> 
> Thanks in advance,
> gn
> 
> 
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-- 
Ryan W. Caudy
Center for Networking and Distributed Systems
Department of Computer Science
Johns Hopkins University