I found this info in the PostgreSQL archives. Here are 2 methods:
Best method from Dan Lyke:
Apache::DBI will pool across Perl programs, and you don’t have to change anything in your scripts.
Next best method from Gilles DAROLD: in your perl script use the following code
use vars qw($dbh); $dbh ||= DBI::connect($datasrc, $dbuser, $dbpwd);
These can be use to create a database connection class in Perl that can handle transparently the connection / reconnection and disconnection for your code. The end use code doesn’t have to be OO, thus the connection object can be reused in any legacy code.