3 Replies Latest reply on Sep 15, 2011 2:26 AM by wdfink

How to detect lost database connection using injected EntityManager?

profinator Sep 13, 2011 9:12 PM

Hi all,

I'm trying to build some reliability and robustness into an application we're running on JBoss AS 6.0.0 and part of this involves being able to handle the loss of a connection to a database on a remote server due to a server failure or network failure. We're using injected EntityManagers to manage the connection to the database:

/***

* Allows access to persistent data.

@PersistenceContext

private EntityManager em;

I've tried using the EntityManager.isOpen method but when I try that I get an error stating that isOpen can't be used with injected instances of EntityManager.

My current solution is to catch RuntimeExceptions (or PersistenceExceptions) when they get thrown by the EntityManager but I'm finding that it can take quite some time before the EntityManager actually throws the exception, leading to long delays in the user interface.

Does anyone know if there's a better way to quickly detect that there's an error with the database connection and handle it appropriately to enhance robustness and provide a better user experience?

Any replies would be greatly appreciated.

Thanks,

Josh.

1. Re: How to detect lost database connection using injected EntityManager?

wdfink Sep 14, 2011 4:07 AM (in response to profinator)

what you want to achieve?
If you use injection it is the responsibility of the container to connections.
You can not control the SQL behind (e.g. a long running query). There is no thread control whether it takes too long, also in most cases the query can not be interrupted.

In most cases the DB connection should work and you should think about the environment if the connection is lost lot of times.
Also you might reconsider the use case if the queries takes long time.
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2. Re: How to detect lost database connection using injected EntityManager?

profinator Sep 14, 2011 7:54 PM (in response to wdfink)

Hi,

What I'd like is to find it out if there is a quick way to test whether or not the remote database is accessible using an injected EntityManager, without having to wait for the EntityManager to start throwing exceptions.

From your resonse it sounds like there isn't an easy way to do it using injected EntityManager because all of the connection work is performed in the container. So maybe the solution is that we shouldn't be using an injected EntityManager, the other option is to manually establish the connection and check whether or not it is still active.

Thanks for the response.
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3. Re: How to detect lost database connection using injected EntityManager?

wdfink Sep 15, 2011 2:26 AM (in response to profinator)

EntityManager uses the containers connection pool.
Here you are able to configure how a DB connection should be checked, e.g. if puplished or periodicaly.

See http://community.jboss.org/wiki/configdatasources for this.
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