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Message-ID: <505A2332.4010306@christopherschultz.net>
Date: Wed, 19 Sep 2012 15:55:30 -0400
From: Christopher Schultz <chris@christopherschultz.net>
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To: Tomcat Users List <users@tomcat.apache.org>
CC: Pid * <pid@pidster.com>
Subject: Re: sessions replication
References: <FBBE2655D8274943AB128D833EFF6EAA03102CB7@IDA025.idanalytics.net>
 <3925735849765296642@unknownmsgid>
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Pid,

On 9/19/12 2:08 PM, Pid * wrote:
> On 19 Sep 2012, at 16:59, "Carrillo, Dan"
> <dcarrillo@idanalytics.com> wrote:
> 
>> Hi folks, My sessions are replicating across the cluster as
>> indicated by my session listener debug output.  E.g I can see the
>> session created/destroyed messages in each respective log. I have
>> a Service object that is serializable, which contains a String
>> member variable (x) which is not initialized; null.  As my load
>> balancer round-robins the requests to each of these servers, each
>> successfully retrieves the service instance from the session.
>> Now, when service.x is set at some point in the workflow, I
>> expect the other members to receive this updated object since it
>> resides in the session.  However, I'm finding that it is not, it
>> remains null in all other containers.
>> 
>> The tomcat config
>> (http://tomcat.apache.org/tomcat-6.0-doc/cluster-howto.html) says
>> that "..For each request the entire session is replicated, this
>> allows code that modifies attributes in the session without
>> calling setAttribute or removeAttribute to be replicated."
>> 
>> Can someone clarify whether I do in fact need to reset the
>> service object on the session in order for it to replicate?
> 
> If by this, you are asking whether you can retrieve an object from
> the session, update it and without adding it back to the session
> expect these changes to be propagated, then no, you can't.

That note in the official documentation certainly is misleading. I
believe that the session is is only marked "dirty" if one of
HttpSession.setAttribute or HttpSession.removeAttribute is invoked. I
think the statement in question indicates that, if the HttpSession is
to be replicated, it will be replicated in full and not piecemeal.

But you still have to call HttpSession.setAttribute in order to
trigger the replication in the first place.

- -chris
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