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From Dain Sundstrom <d...@coredevelopers.net>
Subject Re: Web Clustering : Stick Sessions with NO SHARED STORE
Date Tue, 28 Oct 2003 16:53:02 GMT
On Tuesday, October 28, 2003, at 02:02 AM, Jules Gosnell wrote:

> Bhagwat, Hrishikesh wrote:
>
>> the impact of moving large number of session objects on the network 
>> is a very obvious concern (expressed in the mail thread below)
>>
> if network bandwidth is the bottleneck, then compression is a possible 
> solution. Bear in mind that you are trading cpu and memory 
> requirements for bandwidth.
>
> demarshalling is an expensive thing to do and will affect backup nodes 
> as well as target nodes in migration relationships.
>
> if a backup node can avoid demarshalling incoming objects, then this 
> is a worthwhile optimisation.
>
> compression, which is used in JBoss(tm) SFSB replication is a useful 
> weapon in the arsenal.

I read several research papers on this subject and all seem agree that 
network bandwidth is never the problem (unless your cluster is over a 
wan).  The bottle neck tends to be the IO processing.  Basically, you 
run out of CPU trying to respond to the other nodes lock requests or 
data replication requests.  Anything you can do to reduce CPU overhead 
will improve scalability on the cluster.  Compression and encryption 
are in my opinion a very bad for the back end of the cluster as 
bandwidth inside your data center should be very cheap.  On the front 
end compression and encryption are commonly requirements, but can be 
off loaded to a speciality box (load balancer).

-dain


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