How do I monitor a database for new entries?

Question

I have an application solution which is made up of a web app written in Python (using Django framework) and a Java application which runs on the server.

The web application receives data and stores it into a database queue. The Java application is then to process the received data and also store the results in a database.

My question is how can the Java application be notified that there is new data in the database? Right now, it seems like I will have to regularly poll the database for new data. Is there any way around this?

PS. I have considered running the web app using Jython and using the Observer pattern but my host does not support Servlets.

Answer 1

Unless the database specifically supports it, polling is the only option I know of.

However, if your concern is load on the Java server, you could have another server that does nothing but polls for changes and then notifies your Java server when changes have occurred. I don't know if that is any better than doing a simple polling from the Java server (not knowing your specific problem space and hardware constraints).

Hope that helps.

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Edit: after reading your statement again, it seems like you are already doing a messaging like framework (with the queue in the java application) so the database change could simply be another message that goes into the queue. If it needs priority, you could give the messages priority marks so that they get processed when they need to be processed.