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From Gianny Damour <gianny.dam...@optusnet.com.au>
Subject Re: Clustering Geronimo with Open Terracotta
Date Fri, 16 Feb 2007 22:16:05 GMT
On 17/02/2007, at 3:32 AM, Dave Colasurdo wrote:
<snip>
>
> Tomcat and Mod-jk provide the ability to have the load balancer  
> lock a particular httpsession (identified by session cookie) to a  
> specific cluster member.  This cluster member will serve all the  
> requests for this session until the cluster member tops/fails and  
> failover to a new cluster member  occurs.  This "stickiness" is  
> quite useful for the case of multi-frame JSPs where it is important  
> that all concurrent requests are executing in the same JVM (as per  
> Java EE  specifications).  Hmmm, now that Terracotta provides the  
> concept of a global cross-node JVM, I'm wondering how important  
> this is now .. though still seems there would be  performance  
> overhead in locking across JVMs.. so I think Sticky Session is  
> still useful..

Hi,

I think that if you have sticky load balancing, you do not need to  
acquire a distributed lock to service concurrent requests: requests  
are proxied to the node hosting the session state; each request  
acquires a *local* read lock for the associated session (a read lock  
is acquire such that requests bound to the same session can proceed  
concurrently).

This is only when a request is received by a node where the session  
state cannot be found that a distributed lock is to be acquired.

Thanks,
Gianny



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