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From Tobias Schoessler <tobias.schoess...@gmail.com>
Subject Re: sync cayenne cache in two web apps
Date Thu, 30 Jul 2009 21:23:14 GMT
So thank you for all the suggestions. The solution we finally ended up with
was the one Mike actually suggested intitially. We got our multicast ip,
dropped the latest Jgroups.jar into both webapps lib directories, selected
Jgroups as the Syncronisation mechanism in the cayenne modeller, used the
default jgroups udp.xml config file patched with our multicast ip address
and 'snapp' the contexts were synchronized. Very satisfying - Cayenne
rocks.! :)

Before this I went down the route of trying to make cayenne use the global
JVM scope to store the shared cache. I moved the cayenne.jar up on the
tomcat shared lib directory, out of the two web app lib folders. This did
not work out well, I got stuck at the point where one web app worked fine
the other one threw class cast exception on the mapping objects saying it
cannot cast the types on itself. I assume this is due to the fact that both
webapps had their own copies of the mapping classes. I tried moving them up
into the shared tomcat lib aswell, but  then they could not see the web app
specific classes anymore. So anyway I am happy with our Jgroups solution
now.

The documentation reads lthis setup has some overhead. Does anybody have
experience/numbers how much performance you loose when using jgroups
syncronised caches compared to local cache?

thanks again everyone.

On Thu, Jul 30, 2009 at 10:47 AM, Tobias Schoessler <
tobias.schoessler@gmail.com> wrote:

> Thanks everyone for the posts.
>
> @Mike, I am still not convinced that using the Remote Notification Feature
> is really nessecary here. After all, there seems to be a JVM shared between
> webapps in Tomcat and the article posted seems to proof that there is a
> possiblity to share information between the webapps on a JVM level. So I
> think that using Remote Notification, which I understand to be designed for
> Cross JVM notification creates too much overhead.
>
> You mentioned the possibility of sharing the DataContext between the
> webapps. I think I have to explore this possibility first, as this would
> have less overhead compared to the notification based solution.
> Currently I am using the
> org.objectstyle.cayenne.conf.ServletUtil.getSessionContext(request.getSession())
> to obtain my DataContexts per request.
> If I could change the scope the DataContexts are stored to cross web app
> scope instead of session scope I could share the DataContexts between the
> two web apps. Assuming that I can setup the two webapps to share the same
> session Ids as described in the article.
>
> This might be a no go for me as the two contexts use different
> authentication realms - I have to check this. But even then wouldn't it be
> possbile to configure the cayenne shared cache to use this cross web context
> scope for its shared cache. Then I could use
> org.objectstyle.cayenne.conf.ServletUtil.getSessionContext(session) in the
> two web apps transparently and cayenne would refresh the DataContext from
> this shared cache in the background. Could somebody point me to where this
> shared cayenne cache is configured to have its scope? I assume it uses JVM
> static scope?
>
> @Malcolm, thanks for suggesting this alternative. If I understand you
> correctly you suggest to switch off the cayenne cache alltogether and use
> the jsptag based caching of the OScache project? The problem with this is
> that not all my responses are generated from jsptags. I have many ajax
> requests generating json responses without bothering the jsp container.
>
> Tobias
>
>
> On Thu, Jul 30, 2009 at 3:00 AM, Malcolm Edgar <malcolm.edgar@gmail.com>wrote:
>
>> You can also use OSCache with Cayenne and have the cached queries
>> expire frequently, i.e. after 30 seconds
>>
>> regards Malcolm Edgar
>>
>> On Thu, Jul 30, 2009 at 6:36 AM, Mike Kienenberger<mkienenb@gmail.com>
>> wrote:
>> > Before you make your own custom solution, you might want to read up on
>> > Javagroup.  It might not be a problem to use it in your environment.
>> >
>> > The main page starts off with this:
>> >
>> > http://www.jgroups.org/
>> > ==================================
>> > JGroups is a toolkit for reliable multicast communication.
>> > (Note that this doesn't necessarily mean IP Multicast, JGroups can
>> > also use transports such as TCP).
>> >
>> > [...]
>> >
>> > JGroups comes with a number of protocols (but anyone can write their
>> > own), for example
>> >    * Transport protocols: UDP (IP Multicast), TCP, JMS
>> >
>> > ==================================
>> >
>> > So even if the TCP version doesn't do what you need, you might find it
>> > easier to write your own Jgroup protocol than to write your own
>> > cayenne event bridge.  It's more likely to be documented and there
>> > will be more examples/end users to ask questions of.  There might even
>> > be a tomcat shared session protocol out there somewhere.
>> >
>> >
>> > On Wed, Jul 29, 2009 at 4:16 PM, Tobias
>> > Schoessler<tobias.schoessler@gmail.com> wrote:
>> >> well i am reading this from the documentation:
>> >>
>> >> "... At the minimum, JMS setup requires a JMS server running, and
>> subjects
>> >> for each of the DataDomains to be configured. JavaGroups is
>> peer-to-peer
>> >> library that is embedded into applications. Default configuration
>> provided
>> >> by CayenneModeler will work out of the box, provided that IP multicast
>> is
>> >> enabled on the network."
>> >>
>> >> for the JMS solution the JMS server setup is a problem
>> >> for the JavaGroups setup the "IP multicast is enabled on the network."
>>  is a
>> >> problem
>> >>
>> >> so  for the custom tranport mechanism that you mentioned I stumbled
>> upon
>> >> this here
>> >>
>> >>
>> http://jee-bpel-soa.blogspot.com/2009/06/session-sharing-in-apache-tomcat.html
>> >>
>> >> which seems to describe cross context data sharing on tomcat web
>> contexts
>> >>
>> >> but is there any code to look at to see how a custom transport
>> mechanism can
>> >> be setup?
>> >>
>> >> Tobias
>> >>
>> >>
>> >> On Wed, Jul 29, 2009 at 8:28 PM, Mike Kienenberger <mkienenb@gmail.com
>> >wrote:
>> >>
>> >>> I've never set it up, but it's easily configurable.
>> >>>
>> >>> If you don't like the javagroups or JMS methodologies, you can define
>> >>> your own -- I don't know what tomcat app-data-sharing ability is
>> >>> available -- it probably depends on the container, but I don't
>> >>> remember reading about any in the past.
>> >>>
>> >>> However, the docs seem to indicate that using Javagroups is pretty
>> >>> painless with no external configuration to deal with.
>> >>>
>> >>> I have a Cayenne 1.1.x application I wrote that used remote
>> >>> notification internally to broadcast events between sessions, so I
>> >>> know it's not difficult to set up and define your own event
>> >>> broadcaster.  My guess is that doing it for javagroups is pretty easy
>> >>> since it sounds like a matter of just filling in the forms on the
>> >>> modeler.
>> >>>
>> >>> On Wed, Jul 29, 2009 at 2:15 PM, Tobias
>> >>> Schoessler<tobias.schoessler@gmail.com> wrote:
>> >>> > Thanks Mike,
>> >>> >
>> >>> > so the answer is yes, this can only be done using remote
>> notification? is
>> >>> > this correct?
>> >>> >
>> >>> > Isn't there a way to share the cache among two web application
>> scopes
>> >>> > without going through the hassle of setting up remote notification?
>> >>> >
>> >>> > When the two webapps are running on the same physical machine,
>> inside the
>> >>> > same application server this seems overkill.
>> >>> >
>> >>> > Tobias
>> >>> >
>> >>> > On Wed, Jul 29, 2009 at 6:50 PM, Mike Kienenberger <
>> mkienenb@gmail.com
>> >>> >wrote:
>> >>> >
>> >>> >> Yes,
>> >>> >>
>> >>> >> Here's a Cayenne 2.0 document on it:
>> >>> >>
>> >>> >> http://cayenne.apache.org/doc20/configuring-caching-behavior.html
>> >>> >>
>> >>> >> For 3.0:
>> >>> >>
>> >>> >> http://cayenne.apache.org/doc/configuring-caching-behavior.html
>> >>> >>
>> >>> >> On Wed, Jul 29, 2009 at 12:46 PM, Tobias
>> >>> >> Schoessler<tobias.schoessler@gmail.com> wrote:
>> >>> >> > Hi,
>> >>> >> >
>> >>> >> > is it possible to sync the cayenne cache of two web applications
>> >>> running
>> >>> >> in
>> >>> >> > the same tomcat?
>> >>> >> >
>> >>> >> > I observe one web app showing outdated data when the other
is
>> >>> committing
>> >>> >> > updates. Both apps are using the same mapping configuration.
>> >>> >> >
>> >>> >> > Do I need to use remote notification for this?
>> >>> >> >
>> >>> >> > thanks
>> >>> >> >
>> >>> >> > Tobias
>> >>> >> >
>> >>> >>
>> >>> >
>> >>>
>> >>
>> >
>>
>
>

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