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From Mark Thomas <ma...@apache.org>
Subject Re: Oracle database calling the web app?
Date Tue, 06 Jan 2009 22:28:40 GMT
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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