MySQL: 3.x versus 4.x?

[Marc Schwartz <MSchwartz MedAnalytics com>]

Hi all,

A (hopefully) quick query. Can someone provide some insight into the
selection of MySQL 3.x as opposed to 4.x in Fedora, in light of 4.x
being the present production version series?

Curiously of note, is that the postgreSQL version that is installed is
7.3.4 which is the latest production version of that product.

TIA,

Marc