As more and more users connect to a database, the number of available connections decreases. You can conserve the number of connections by connecting temporarily, and then disconnecting when the application is done accessing the database. This frees up the connection for another user. If the number of available connections is scarce, an application should release connections wherever possible.

However, each connect and disconnect generates connection overhead, which is the sum of operations necessary for an application to connect and disconnect a database. The time used for connection overhead depends on the nature of the database connections. A connection to a database over a network generally takes longer than a connection to a local database. While the application connects to a database, the end user waits.

When there are plenty of available connections, you might want to reduce the number of connects and disconnects to minimize overhead. The best way to do this is to connect all application databases only once at application startup. With this technique, all connection overhead occurs once at application startup and does not occur again throughout the life of the application.