Will r2d2 create more connections than max_size when using builder()?

[RKochenderfer]

My question is the title. The database I'm using has a very small number of connections allowed and I would like to make sure that the active connections does not exceed 4.

 let tmm10_pool = r2d2::Pool::builder()
            .max_size(4)
            .build(ODBCConnectionManager::new(&config.tmm_conn_string))?;

Will the code above ever allow a 5th connection to be created?

[sfackler]

The maximum size is the maximum number of connections the pool will maintain concurrently.

[RKochenderfer]

So just to clarify for myself as I'm relatively inexperienced with connection pooling, if there are currently 4 connections being used and a 5th one needs to be made, will r2d2 make the 5th connection wait till another connection is dropped or will it make a 5th connection that isn't maintained by the pool?

[sfackler]

If the number of active connections is at the max_size, the pool will not make more connections.