…ue is Leq 0 a warning over the python logging system ist emitted.

Connections are now checked only against the max_open property.

…ant for two reasons: First if you have a software system and you chose to use database pools you should be aware of how many connections may be opened to the database servers. Especially when using micro-services where more than one service accesses the database. Second initializing values with unlimited is useless, because there is no such thing as infinite connections to servers or the like.

If the values are not initialized properly a ValueException is raised to indicate that the initialization is wrong.

…nnection pools. This change is not backwards compatible. The reason for this is, that the default initialization is not useful.