Wait several milliseconds if the number of connections exceed certain number but not maxConnections

[tomyeh]

In a system with heavy load, it can allow all connections allowed (maxConnections). However, if many of these connections are short lived, we can reduce number of connections by waiting a while when the number of connections exceeds a certain number, say, freeConnections.

In other words, the connections are likely to release before we allocate a new one.