Freeradius 3.0 - SQL - spare connections?

[Andre Schwarzer]

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