[jdjlist] RE: Caching of semi-static data across webapps

Matt Liotta Tue, 04 Mar 2003 17:12:41 -0800

Title: [jdjlist] RE: Caching of semi-static data across webapps

If the DB solution looks interesting, but you are concerned about the performance issues associated with hitting a DB so much you might want to use a shared file system. A shared file system is a nice solution since the file system takes care of blocking I/O on individual files even when shared across a cluster. Further, these solutions are built to scale and don’t have any of the overhead associated with DBs.

Matt Liotta
President & CEO
Montara Software, Inc.
http://www.montarasoftware.com/
888-408-0900 x901

-----Original Message-----
From: Greg Nudelman [mailto:[EMAIL PROTECTED]
Sent: Tuesday, March 04, 2003 6:45 PM
To: jdjlist
Subject: [jdjlist] RE: Caching of semi-static data across webapps

Yan, DB solution is not that bad! I heard of very successful set ups that put the entire application-specific info into a DB record that is read on start-up (like the XML config file, but this is instantly propagated to all of your 20 machines through the DB, your single point of contact). Ideally all your machines come up and read that record. To deploy your fix you can have a low priority thread that tries to check for any changes every 1-5 minutes via a time-stamp (better), or for an even more brutal approach, restart all your apps in sequence after the fix has been deployed (worse and will take longer then 5 minutes for 20 machines).

I like the JMS less, because it would take a lot of coding to set up this framework on our non-standard setup. If you got the standard J2EE system, then it sometimes comes pre-packaged. However, if it's a 1-time thing just for your cache, DB solution is arguably easier to build and test.

Greg the XP man is pushing his 2 cents.

-----Original Message-----
From: Yan, Hong [IT] [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, March 04, 2003 3:14 PM
To: jdjlist
Subject: [jdjlist] RE: Caching of semi-static data across webapps

Thanks for suggestions. I can see using JMS is an elegant solution!

However, our project does not have JMS, and I do not expect the management
will approve the use of JMS only because of the messaging need to
synchronize the caches.

For this project, I have to find another alternative solution.

Thanks again.

Jeff

-----Original Message-----
From: Bill Wang [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, March 04, 2003 5:59 PM
To: jdjlist
Subject: [jdjlist] RE: Caching of semi-static data across webapps

I agree with Dave. Since you are using WebSphere app server, the JMS
solution is a better choice. You can use the publisher and subscriber
mechanism on a topic. You can have your webapps to subscribe with a topic.
Once one webapp triggers the load, it will notify a controller which
triggers your JMS to publish the latest translation to the topic. Whoever
subscribes the topic will get the lastest update. In your case, it will be
your cloned webapps.

Hope this helps.

"Dave Hanson" <[EMAIL PROTECTED]> on 03/04/2003 04:59:51 PM

Please respond to "jdjlist" <[EMAIL PROTECTED]>

To: "jdjlist" <[EMAIL PROTECTED]>
cc:

Subject: [jdjlist] RE: Caching of semi-static data across webapps

The requirement seems to be implementation of a notification method. The DB
solution, though a bit brute force, will work. A more elegant solution
would be to implement a permanent queue message via JMS on a subject. All
of the start-up servlets would populate from the database and block for a
message based on the subject. Once the correct message was received, the
database refresh could be accomplished.

Additional granularity could be added to limit the refresh based on message
content; i.e. only refresh the German translation.

J two cents added

      -----Original Message-----
      From: Yan, Hong [IT] [mailto:[EMAIL PROTECTED]]
      Sent: Tuesday, March 04, 2003 4:29 PM
      To: jdjlist
      Subject: [jdjlist] Caching of semi-static data across webapps

James :

      Thanks for sharing the ideas. As this is getting interesting, I would
      like to explain what I do, and the problems that I have in more
      detail :

      I have a Singleton object that keeps several hashtables (with
      Spanish/Chinese/Japanese/French/Germany texts and key strings for
      these texts). These hashtables will be populated a start-up servlet
      when the webapp starts. JSP pages retrieves the locale texts using
      keys, so that the web system is translated in user's preferred
      locale.

      Let me take a simplified version, I have one WebSphere server with
      three webapp clones in load balance. My server never stops, so when
      translators need modify these locale texts, I need to reload the
      corresponding hashtables.

      The thing is, on a webapp based system, the translator can trigger a
      reload, and this reload happens in only one of the clones, and the
      other two clones are not refreshed. Users hitting these two clones
      are still getting old translation.

In a word, in my system, the cached data is semi-static, and need to
be reloaded on demand.

Right now we are working on possible design approaches to fix this,
and we figure one of the followign may do the job:

(1) Use a database flag and let the Singleton object keeps on polling
this flag. Once flipped, the object will refresh the content.

(2) ...

      But I assume this should be a common problem to any system with
      multiple webapps in load balancing, and there should be a systematic
      solution...Any suggestions are welcome.

Thanks

      Jeff
            -----Original Message-----
            From: James Stauffer [mailto:[EMAIL PROTECTED]]
            Sent: Tuesday, March 04, 2003 3:54 PM
            To: jdjlist
            Subject: [jdjlist] RE: Caching

            We have a servlet that gathers the data about the caches and
            serializes that info. One servlet connects to the other
            servlets to get that info and consolidates it.

James Stauffer

            -----Original Message-----
            From: Yan, Hong [IT] [mailto:[EMAIL PROTECTED]]
            Sent: Tuesday, March 04, 2003 2:02 PM
            To: jdjlist
            Subject: [jdjlist] RE: Caching

James:

            Thanks for the post. I am also interested in caching objects
            and right now I am having problems in refreshing them - I have
            three WebSphere sites, each one of them has three webapp
            clones.

How do you manage the caches across sites?

Thanks

            Jeff
                  -----Original Message-----
                  From: James Stauffer [mailto:[EMAIL PROTECTED]]
                  Sent: Tuesday, March 04, 2003 2:48 PM
                  To: jdjlist
                  Subject: [jdjlist] RE: Caching

                  We have our own internally developed object cache. It
                  uses a hard cache (can't be GC'ed) extended by a soft
                  reference cache. It also has a cache manager servlet and
                  another servlet to manage the caches across machines. It
                  mostly only caches objects of the following:

public interface CacheAble {
public int getID();

public String getClassName();

public String getDescriptor();
}

If you are interested I can probably give more design
details.

James Stauffer

                  -----Original Message-----
                  From: Greg Nudelman [mailto:[EMAIL PROTECTED]]
                  Sent: Tuesday, March 04, 2003 12:56 PM
                  To: jdjlist
                  Subject: [jdjlist] Caching

                  We're have a home-grown Java application and would like
                  to introduce some kind of app-level cache manager. I'm
                  interested if someone has made anything like that --
                  shareware/custom packages, a study about the size of
                  objects in memory, anything like that.

All suggestions welcome. Thanks!

Greg

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[jdjlist] RE: Caching of semi-static data across webapps

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