Looks like there is a old implementation diesel-rs/ r2d2-diesel that shouldn't be used anymore
THIS CRATE HAS BEEN DEPRECATED, USE THE r2d2 MODULE IN DIESEL INSTEAD
Where to find a concrete up-to-date implementation of DIESEL using connection pool R2D2 to interact with a postgresql database ?
Looking into https://github.com/TechEmpower/FrameworkBenchmarks there is not use of connection pool which looks weird to me...