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From Dwayne <>
Subject Re: [OT] Session replication vs stateless
Date Fri, 24 Aug 2007 21:04:27 GMT
Have you considered distributed caching for session replication?  I avoid
stateless like the plague.

There are several tools out there for this, but my favorite (because they
are open source) is Terracotta.  It clusters the JVMs.
Native clustering in Tomcat putters out, in my experience, after 3 nodes.
With Terracotta, I dropped in the code and now am clustering 5 nodes and
getting a lot higher TPS.
I think it is worth the hour it took me to implement it and I didn't have to
change my code at all, just write a short XML and drop some tags around what
I wanted to distribute.
Get it at  The support docs do not say they support Tomcat 6
yet, but I have yet to hit any bugs (3 weeks in).

On 8/24/07, lightbulb432 <> wrote:
> Although the debate between session replication vs stateless can't be
> definitively solved and depends on the application, I'd like to hear about
> your experiences with both. How are you designing your current
> applications,
> and what implications has the choice that you might not have expected -
> would you do anything differently if you could?
> I ask because I'm still unsure about whether to decrease memory usage by
> increasing database usage (or bandwidth usage if sending state back to the
> client) by going stateless at the application tier.
> Stateless
> Are there any people using stateless application tiers with transactions
> that are inherently stateful, such as wizard-type screens or other
> business
> processes or workflows? How'd that turn out?
> Did you choose to move this state to the client (through cookies) or to
> the
> database?
> Session replication
> For session replication in Tomcat 6, what's the ideal replication group
> size
> in general? Would you ever want to set it to more than 2 instances?
> (Because
> for any more, then you'd have a lot more overhead in transferring state
> back
> and forth to even more other instances...)
> With session replication between 2 machines, are you effectively reducing
> the capacity of each server, at least in terms of memory, by 50%?
> Hopefully
> I'm looking at it the wrong way, because it not, I'm not really liking the
> session replication idea if I'm decreasing hardware usage by half.
> Thanks.
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