Some servers would pick up the missing database immediately and start producing errors to the servers log file. This is usually the case if you use standard data sources such as in
J2EE.
Other servers (or if the database connection is hard-coded via
JDBC calls in the application code) would only detect errors if database queries were issued while the database was down. After all, you can't run queries on a server that isn't available.
In all cases though, the application server should be able to detect when the database server is back up and start working again. The only downside is that if you have any cached objects from the database on the application server, they may need to be resynched, ergo a restart of the application server may be required if your persistence manager does not handle this.
[ December 07, 2005: Message edited by: Scott Selikoff ]