A connection pool is created in the process of creating each unique connection string that an application uses. When a pool is created, it is populated with enough connections to satisfy the minimum pool size requirement, set by the Min Pool Size connection option. The maximum pool size is set by the Max Pool Size connection option. The driver allocates additional connections to the pool until the number of connections reaches the value set by Max Pool Size.
Once the maximum pool size has been reached and no usable connection is available to satisfy a connection request, the request is queued in the driver. The driver waits for the length of time specified in the Login Timeout connection option for a usable connection to return to the application. If this time period expires and a connection has not become available, the driver returns an error to the application.
A connection is returned to the pool when the application calls SQLDisconnect. Your application is still responsible for freeing the handle, but this does not result in the database session ending.
