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From Peter Rossbach ...@objektpark.de>
Subject Re: Are Sticky Sessions really necessary?
Date Sat, 03 Nov 2007 05:14:33 GMT
Hi,

It is not only ineffizient and a risk, Read 7.7.2 at the spec:

SRV.7.7.2 Distributed Environments
Within an application marked as distributable, all requests that are  
part of a session
must be handled by one Java Virtual Machine1 (“JVM”) at a time. The  
container
must be able to handle all objects placed into instances of the  
HttpSession class
using the setAttribute or putValue methods appropriately.
....

regards
Peter

Am 02.11.2007 um 22:37 schrieb Len Popp:

> You can indeed use session replication without sticky sessions, and
> the session data will be copied to all the Tomcat servers. However it
> may be inefficient. You probably have to use synchronous replication
> to ensure the session data is consistent across the cluster, which
> adds latency to the requests. And there could be a lot of extra
> network traffic in the cluster if it's busy (which it is, otherwise
> you wouldn't be doing load balancing).
>
> (I haven't used session replication in a high-load situation. Maybe
> someone else can tell us how well it works.)
> -- 
> Len
>
> On 11/2/07, Stephen Wick <swick@nicholsonkovac.com> wrote:
>> The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make  
>> sure
>> that your loadbalancer is configured for sticky session mode."   
>> However,
>> I don't see the term "Sticky" sessions anywhere in the Servlet 2.3 or
>> 2.4 specifications.
>>
>> Are sticky sessions really required for clustering to function  
>> properly
>> in Tomcat 5.5?  I thought that session replication would eliminate  
>> any
>> need to direct a client session to one node in a cluster.
>>
>> If not, can we adjust the documentation to indicate that Sticky  
>> sessions
>> are optional, for the appropriate reason (I'm guessing the advent of
>> session replication in tomcat.)
>>
>> I am asking this question because I am having trouble with Sticky
>> sessions in my load balancer, and I need to know whether or not I  
>> should
>> pursue fixing this feature.  If tomcat doesn't really require sticky
>> sessions, then I can leave my load balancer alone.  If tomcat does  
>> need
>> the feature to function properly, then I need to go to some  
>> additional
>> expense to resolve the issue with my load balancing appliance.
>>
>> Thank you for your time and expertise.
>>
>> Stephen Wick
>> Interactive Developer
>> Nicholson Kovac, Inc.
>>
>> References
>> http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
>>
>
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