Freeradius 3.0 - SQL - spare connections?

Hello, have installed a new freeradius 3.0, bevor i worked with the Version 1. I see in my Test´s, in the radius.log the Messages below. I don´t know what are spare Connections, what they do and for what the radius use this. Additional i don´t know why i get this messeges with the Default Settings. Can some one explain me the usage of the spare Connections, best by an example. Wed Jul 15 13:34:25 2015 : Info: rlm_sql (sql): 0 of 5 connections in use. Need more spares Wed Jul 15 13:34:25 2015 : Info: rlm_sql (sql): Opening additional connection (12) Regardes