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From "Edward Dowgiallo" <eddowgia...@gmail.com>
Subject Re: Oracle database calling the web app?
Date Tue, 06 Jan 2009 22:34:44 GMT
It is not necessary to poll an Oracle database.  Advanced queueing in
combination with triggers provide an event driven framework.

Ed

On Tue, Jan 6, 2009 at 5:28 PM, Mark Thomas <markt@apache.org> wrote:

> Bill Davidson wrote:
> > Is it possible to set up a callback like situation so that a trigger in
> an
> > Oracle 10g database can call a method in a currently running webapp
> > that's running in Tomcat 6?
> >
> > My situation is that I want to cache some infrequently changed database
> > data in memory but when that data does change in the database, I want
> > the web applications, running on multiple servers, to immediately pick
> > up the change.
> >
> > Right now, one idea I have for this is to have the database trigger
> > create a file in a file system that's shared by the database server and
> > the application servers and have the web apps check for the existence
> > of this file to know whether to update the cache.  It feels ugly and
> > means hitting a networked file system a lot but it seems like it should
> > work and it seems like it should not be as bad as hitting the database
> > constantly for something that doesn't change very often.
> >
> > I'd rather have the database send a message somehow to the web app that
> > it needs to update its cache of the data.  Any suggestions?
>
> 1. JMS?
> 2. Call an reload servlet from the database?
> 3. Drop the immediate update requirement and poll a data changed flag in
> the db
> every x seconds?
>
> Personally, I'd go with 3. For a simple flag this could be every few
> seconds
> with very little load on the db or Tomcat and would take all of a few
> minutes to
> code.
>
> Mark
>
>
>
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