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From Bruce Snyder <>
Subject Re: Clustering
Date Sun, 16 Oct 2005 23:27:11 GMT
On 10/15/05, Jules Gosnell <> wrote:

> >> WADI currently sits on top of ActiveCluster, which it uses for
> >> membership notification and ActiveMQ which is used for transport by
> >> both 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 an API). So you do not need to choose between
> >> WADI and ActiveCluster - they 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)
> >> and it looks as if WADI and ActiveSpace will become more closely
> >> aligned. So 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 source approaches to this problem-space.
> >>
> > Can you provide a quick high level description of the advantages of
> > WADI over Tomcat and Jetty clustering solutions?
> Jetty uses 1->all replication over jgroups, as I believe 1 Tomcat
> session manager does. I think the other Tomcat session manager also does
> 1->all replication, but over its own protocol. Perhaps Jeff can confirm
> this. I think TC's 'PersistentManager' is also able to write changed
> sessions out to disc at the end of the request.
> 1->all, for the reasons given above will not scale. The more nodes you
> add, the more notifications each will have to react to and the more
> sessions it will have to hold. you are simply deferring your problems
> for a little while. Your only way out is to partition cluster and
> sacrifice your availability. When WADI's in-vm replication strategy is
> finished, I think that this will make it a clear winner for anyone
> wishing to cluster more than  2-3 nodes.

I know that this may sound a bit off the wall, but what about
implementing the BitTorrent protocol
( The purpose of the
BitTorrent protocol is to redistribute the cost of downloading a file
of (potentially) unlimited size to the downloaders themselves by
automatically recruiting the downloaders to upload chunks of the file
to their peer downloaders. There's a very good paper available
( that outlines the
BitTorrent protocol at a higher level and explains the economic theory
around which the protocol was built and how it has already been proven
through it's many implementations and high utilization throughout the
world today.

perl -e 'print unpack("u30","D0G)U8V4\@4VYY9&5R\"F)R=6-E+G-N>61E<D\!G;6%I;\"YC;VT*"

The Castor Project

Apache Geronimo

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