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From Mike Kienenberger <mkien...@gmail.com>
Subject Re: sync cayenne cache in two web apps
Date Thu, 30 Jul 2009 21:43:24 GMT
I don't remember the specific implementation, and it might vary for
JavaGroups over what is used internally.  You really don't need to use
multicast if you only have two apps.   I'd go with the TCP setup, both
for reliability and to limit the impact on the rest of the network.
The same traffic probably goes over the wire, but the other machines
won't process those packets.

Your best bet is to look at the EventBridge code and see what kind of
data it sends out.  It might vary between event types if it doesn't
simply fault those objects.

On Thu, Jul 30, 2009 at 5:37 PM, Tobias
Schoessler<tobias.schoessler@gmail.com> wrote:
> yes that's what I observe too. The messages sent when these updates occure,
> do they contain the change infromation or only the information which objects
> to invalidate? I got this asked when I asked for the multicast address, to
> estiamte traffic for this setup.
>
> On Thu, Jul 30, 2009 at 11:33 PM, Michael Gentry <mgentry@masslight.net>wrote:
>
>> Hi Tobias,
>>
>> I've not used the cache synchronization before, but I was under the
>> impression that the main overhead is when inserts/updates/deletes are
>> done, not when selects are done.  When you do an insert/update/delete,
>> that information must be broadcast, but selects do not.  I'm sure
>> someone will correct me if I am wrong on this.  :-)
>>
>> mrg
>>
>>
>> On Thu, Jul 30, 2009 at 5:23 PM, Tobias
>> Schoessler<tobias.schoessler@gmail.com> wrote:
>> > 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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