Your JMS approach sounds fairly sophisticated; could take a while to implement ;-)
Hibernate provides some out-of-the-box cacheing implementations, some of which take on this problem. I think you'll find this portion of their user guide fairly relevant:
http://www.hibernate.org/hib_docs/reference/html_single/#performance-s3
In particular, the SwarmCache and JBoss TreeCache look like they could do what you're looking for. I bet they could be used outside Hibernate too, but I'm not sure.
Matt
Mike Duffy wrote:
Thanks Christian,
Let me give you a specific example of what I am trying to do.
I have several different sets of label/value pairs that are stored in database tables. These label/value pairs make up the select options and other interface options for web pages in the application. The options do not change that often, so rather than going back to the database each time a page is displayed, I'd like to store the options in maps that are stored in application scope and easily accessible through JSTL.
On the occasion that the options do change, I'd like to reload the applicable maps to all servers
in the cluster.
It seems like this would be a good feature for Tomcat to have, but from reading the documentation it seems that the feature is not there.
Perhaps some sort of JMS broadcast service would do the trick. Does any one have any suggestions?
Mike
--- Christian Bollmeyer <[EMAIL PROTECTED]> wrote:
On Saturday 10 April 2004 21:48, Mike Duffy wrote:
Hi,
I've read documentation for The Tomcat 5 Servlet/JSP Container: Clustering/Session Replication HOW-TO http://jakarta.apache.org/tomcat/tomcat-5.0-doc/cluster-howto.html
I understand clustering for individual user sessions. Are there any
correlated methods for clustering application scope objects?
AFAIK there's nothing in the Servlet API specifications in this direction. Sessions may be swapped in and out by several different means (serialization or database), but application scope information is kept individually for each JVM.
The J2EE API for the Interface ServletContext states, "In the case of
a web application marked "distributed" in its deployment descriptor,
there will be one context instance for each virtual machine. In this
situation, the context cannot be used as a location to share global
information (because the information won't be truly global). Use an
external resource like a database instead."
Yes. But then, it makes no difference whether your application is marked as 'distributable' or not when considering application scope objects. Application scope is always limited to a single JVM. 'Distributed' is about sessions only.
Rather than use a database, what I would like to be able to do is make a call to
servlet.getServletContext().setAttribute(key, object);
and have the object stored in the application scope of all servers in
the cluster.
That surely would be desirable, but I don't know of any 'official', declarative means to achieve such behavior. Then: automatically synchronizing application scopes between several JVM instances would cause a lot of additional synchronization troubles - who determines what's the actual system state at a given point, e.g. if you update an application scope object (that is globally shared) on one server, and another user does likewise on a second one, what should be the end result? And so on.
I know that EJBs were designed to serve this purpose; however, IEJBs live in the backend and are independant from
would like to bypass the overhead and complexities of EJBs.
the web tier. Looking at the problem from a web tier view (which is what Struts is about),
it should not make any difference whether the
information comes directly from a database
in the end or from an EJB tier in-between.
That's transparent. Anyway, using EJBs
won't solve your problem in the end, for
it's an entirely web tier specific issue,
and EJBs are not part of that.
If there isn't a switch that can be flipped in Tomcat, there might beThere is no switch (remember the spoon
a way to create a lightweight JMS administration class to serve this
purpose. Has anyone tried this?
boy in Matrix I ? :-). But the JMS idea is
interesting. Never actually tried it, but
of course, you can always handle
application specific logic programma-
tically, including using JMS for updating
application scopes in a distributed environment. But I never tried.
If the answer to this question is RTFM, please send a link; I've looked through the documentation and I can't seem to find a clear reference.
Thanks for your time and consideration.
Just some thoughts that came to me on early Easter Sunday :-) Let's better say: night; it's 2:16 local time here. So I should better go to bed.
Mike
HTH, -- Chris.
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