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From "Surendra Reddy" <>
Subject RE: Clustering
Date Sun, 16 Oct 2005 04:31:38 GMT
We, at Optena, are also working a proposal Geronimo Grid Architecture.
How can we involve and contribute in this activity?


Surendra Reddy
Founder and Chief Technology Officer
Optena Corporation
2860 Zanker Road,
San Jose, CA 95135

-----Original Message-----
From: Dave Colasurdo [] 
Sent: Saturday, October 15, 2005 5:05 AM
Subject: Re: Clustering

Jules Gosnell wrote:
> Jeff Genender wrote:
>> Now that we have achieved the covetted J2EE Certification, we need to

>> start thinking about some of the things we will need to have in 
>> Geronimo in order to be mass adopted by the Enterprise.
>> IMHO, I think one of the huge holes is clustering.  This is a heavy 
>> need by many companies and I believe that until we get a powerful 
>> clustering solution into G, it will not be taken as a serious J2EE 
>> contender.
>> So, with that said, I wanted to start a discussion thread on 
>> clustering and what we need to do to get this into Geronimo.  I 
>> personally would like to be involved in this (thus the reason for me 
>> starting this thread) - yeah, since Tomcat is done, now I am bored
>> I was going over the lists and emails and had some great discussion 
>> with Jules on the WADI project he has built.  This seems compelling
>> me.  I also noticed Active Cluster as a possibility.
>> So lets start from the top.  Do we use an already available clusering

>> engine or do we roll our own?  Here is a small list of choices I have

>> reviewed and it is by no means complete...
>> 1) WADI
>> 2) Active Cluster
>> 3) Leverage the Tomcat Clustering engine
>> So here are some of my questions...
>> How complete is WADI and Active Cluster?  Both look interesting to
>> My only concern with Active Cluster is it seems to be JMS based,
>> I think may be slow for high performance clustering (am I incorrect
>> this?).  How mature is WADI?
> Here is a status report on WADI.
> I'm developing it full time.
> A snapshot is available at - documentation is in the

> wiki - at the moment the documentation (rather minimalist) is more up
> date than the snapshot, but I will try to get a fresh one out next
> WADI is a plugin HttpSession Manager replacement for Tomcat-5.0/5.5
> Jetty-5.1/60 (it can actually migrate sessions between all four in the

> same cluster).
> It comprises a vertical stack of pluggable caches/stores (memory,
> disc, db etc) through which sessions are demoted as they age and 
> promoted as and when required to service a request.

Can you please clarify the purpose of promotion/demotion of 
httpsessions? Is this a mechanism to age old entries out of the cache? 
How does this relate to httpsession inactivity timeouts?
Is the cache size configurable?

> This stack may be connected horizontally to a cluster by inserting a 
> clustered store, which uses a distributed hash table (currently 
> un-replicated, but I am working on it) to share state around the 
> clusters members in a scalable manner. WADI has a working mod_jk 
> integration.

Does this mean that each cluster member shares it's httpsession data 
with all of the other members (1-> all) or is there the notion of 
limiting the httpsession replication to one (or a few) designated 

> WADI currently sits on top of ActiveCluster, which it uses for 
> membership notification and ActiveMQ which is used for transport by
> layers. ActiveMQ has pluggable protocols, including a peer:// protocol

> which allows peers to talk directly to one another (this should put to

> bed fears of a JMS based solution not scaling - remember, JMS is just
> API). So you do not need to choose between WADI and ActiveCluster -
> are complimentary. ActiveCluster can also (I believe) use JGroups as a

> transport - I haven't tried it.
> ActiveSpace is another technology in this area (distributed caching)
> it looks as if WADI and ActiveSpace will become more closely aligned.
> this may also be considered a complimentary technology.
> Both Tomcat and Jetty currently have existing clustering solutions. I 
> looked closely at the Tomcat solutions before starting out on WADI and

> knew all about the Jetty solution, because I wrote it :-). WADI is my 
> answer to what I see as shortcomings in all of the existing open
> approaches to this problem-space.
Can you provide a quick high level description of the advantages of WADI

over Tomcat and Jetty clustering solutions?

> Some parts of WADI should soon (December) be undergoing some serious 
> testing. When they pass we will be able to consider them production 
> ready. Others, notably the distributed hash table are still under 
> development (although a fairly functional version is available in the 
> I think that, in the same way Tomcat clustering could be enabled
> in Geronimo, WADI could also be added by virtue of its integration
> Tomcat/Jetty, but I have been concentrating on my distributed hash
> too hard. If anyone is interested in talking further about WADI,
> trying to plug it into Geronimo (It is spring-wired and uses spring to

> register its components with JMX. I guess it should be simple to hook
> into the Geronimo kernel in the same way, I just haven't had the
> or helping out in any way at all, I would be delighted to hear from
> I have broached the subject of a common session clustering framework 
> with members of the OpenEJB team and we have discussed things such as 
> the colocation of HttpSessions and SFSBs. I believe OpenEJB has been 
> moving towards JCache to facilitate the plugging in of a clustering 
> substrate. My distributed hash table is also moving in the same
So, if I understand correctly, you are working towards some common 
infrastructure with openejb.. though WADI itself, will not address 
clustering beyond the Web Tier?

Thanks for the update!

> I hope that gives you all a little more information to go on. If you 
> have any questions, just fire away,
> Jules
>> Thoughts and opinions are welcomed.
>> Jeff

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