You need to be running inside mod_perl to take advantage of Apache::DBI connection pooling persistent connections. Please note that you don't need to write any script in mod_perl :) you only need to write some robust Perl code using strict and warnings, plus few simple rules that you can read here: CGI to mod_perl Porting.

There are some alternatives to mod_perl, like Persistent Perl, but you still need to write code following all the rules that apply to persistent environments.

Ciao, Valerio

Update: thank you very much perrin for the correction.