On 12/27/06, Rainer Jung <rainer.jung@(protected):
>
> Hi,
>
> Li Ma schrieb:
> > 1. I was told Tomcat can only run max 3 nodes in cluster smoothly.
> What's
> > your milage?
>
> Cluster in the sense of horizontal scaling (load-balancing): no
> limitations.
>
> Cluster with state replication of sessions (assuming TC 5.5): you break
> down your cluster into groups of 2 to 4 nodes, and replucation is
> any-to-any inside a group and no replication between groups. Technically
> spoken a group is a cluster of nodes and your whole farm consists if
> many small clusters. mod_jk load-balancing can be configured to respect
> those clusters during fail-over by defining "domains" in mod_jk.
>
> Be careful: state replication is complicated and expensive. If your
> session doesn't have a lot of value and it's cheap for your costumers to
> relogin after node failure, you don't want to use state replication.
> Horizontal scaling and a good load-balancing suffices in this case. Only
> if sessions are valuable, you might want to protect them against failure
> by real clustering.


Just to note that Terracotta sessions clustering is now open source(
http://terracotta.org/confluence/display/orgsite/Download)
See some benchmark info here :
http://www.kodewerk.com/terracotta_sessions_benchmark.htm

I know that terracotta can help you cluster with sessions for upwards of 100
nodes!

BR,
~A


> 2. This is not related to Tomcat, but if a site has N registered users,
> > what
> > is the average percentage of concurrent user should I expect? I ask this
> > because my client wants 1million registered users. But he wants me to
> > support 20% concurrent users, which I believe is way impossible! But I
> need
> > to have some number to give him the right sense. This is also important
> for
> > me to setup the target.
>
> This really depends mostly on the business.
>
> Concurrent Users = Number of sessions ~ Memory constraints
> Concurrent Requests = Concurrent Users * Click Rate of User * Response
> duration of request ~ CPU and Thread constraints
>
> Concurrent Users and Click rates very much depend on the business the
> app provides. Some Aps are used as "Login in the morning, keep session
> open all day and expire during night", others are "Login, do something
> and log out/expire".
>
> Click rates can be very high (Ajax, static requests, fine grained user
> interfaces" or low "transaction type system, long prepartion times
> locally in browser for complex forms".
>
> Regards,
>
> Rainer
>
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--
BR,
Anjan Bacchu
Summit Information Systems