Hi, We want to have a function in the process which would check

Why don't you just use the <check-valid-connection-sql> element in your appian-ds.xml ?

Well i got the same issue and waiting response...What i used to Query node and Select Database=1 measn DB is connected to appian otherwise not.

Eduardo: How could we use that in a process model? We have to fire a lot of queries to external DB and it can be a case that DB is down. Hence, want to check it just before the calls to DB.

No, that setting is to force JBoss to re-connect if the DB goes down but I agree won't prevent the node from failure. You could create a custom smart service that would run this simple select and catch the exception gracefully so you can wait for the reconnection to happen in your model (reconnection will happen if you use this setting in appian-ds.xml and if the DB becomes available again)